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Jul - American Radio History

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1. JULY 1978 Volume 31 No 11 Published Monthly 2nd of preceding Month First Published 1947 Incorporating The Radio Amateur Editorial and Advertising Offices 57 MAIDA VALE LONDON W9 1SN Telephone Telegrams 01 286 6141 Databux London Data Publications Ltd 1977 Contents may only be reproduced after obtaining prior permission from the Editor Short abstracts or references are allowable provided acknowledgement of source is given Annual Subscription 7 00 Overseas 8 00 U S A and Canada 15 00 includ ing postage Remittances should be made payable to Data Publications Ltd Over seas readers please pay by cheque or International Money Order Technical Queries We regret that we are unable to answer queries other than those arising from articles appearing in this magazine nor can we advise on modifications to equipment described We regret that such queries cannot be answered over the telephone they must be submitted in writing and accompanied by a stamped addressed envelope for reply Correspondence should be addressed to the Editor Advertising Manager Sub scription Manager or the Publishers as appropriate Opinions expressed by contributors are not necessarily those of the Editor or proprietors Production Web Offset Vate London W9 1SN by Swale Press Ltd JULY 1978 Published in Great Britain by the Proprietors and Publishers Data Publications Ltd 57 M
2. lt is confirmed Smithy The capacitor loses a bit of its charge during the first part of the scan sec tion of the cycle but it still retains enough to provide a voltage which is considerably positive of the h t positive rail With simple line out put transformer circuits you can always find the boosted positive voltage because it s sitting at the top end of the winding whose bot tom end goes to the line output valve Or nowadays to the line out put transistor In the older sets the boosted h t voltage was normally used to supply the frame timebase EHT rectifier gt EHT gt winding oscillator and do similar jobs where fairly high voltage was needed Ts there a boosted positive supp ly in this transistor circuit Smithy pointed to the circuit in the service manual Fig 3 b There it is he stated right at the top of the line output transformer primary winding just as with the valve version Since the supply voltage in this set is only about 11 5 volts the boosted voltage is correspondingly low In practice it s approximately 25 volts and it s used for supplying the i f stages and part of the video amplifier But it does not supply the video output stage which requires a much higher voltage Humph repeated Dick He thought for a moment What voltages he asked does the line output transformer provide other than the boosted supply voltag
3. Average voltage Fig 5 According to the way connections are made to it winding on a ling output transformer may produce flyback pulses which are positive going with respect to chassis as in a or scan pulses which are positiva going as in b which the spot travels across the picture tube screen Smithy drew the waveform with its average voltage carefully Fig 5 a SCAN PULSES Now that waveform said Dick musingly is the one that s passed to the e h t rectifier That s right agreed Smithy and as we ve already said it s got positive going flyback pulses An agonised expression creased Dick s face T think I m beginning to unders tand what this scan pulse Pee is about he stated slowly Am I right in saying that it is all 1 right to pass spaced out positive going flyback pulses to the e h t rectifier because the e h t current is so small You are The e h t reservoir capacitor is charged up by each pulse and the small e h t current only discharges it a little bit before the next pulse comes along Right said Dick briskly Now what happens if we want the line output transformer to supply a cir cuit that requires a high current could we do that by turning the waveform upside down so that the flyback pulses go negative Fig 5 b JULY 1978 We could Blimey remarked Dick delightedly I think I v
4. The circuit of the receiver appears in Fig 1 It has four stages a grounded gate input stage a syn chronous detector a common emitter audio pre amplifier and a common emitter output stage hilst the grounded gate Jugfet in the TR1 posi tion provides a small amount of gain its primary function is to isolate the aerial from the detector TR2 Such isolation is necessary because the detec tor is oscillating in use with the result that the receiver could otherwise radiate a signal which would interfere with other sets R1 is the source bias resistor for TR1 and no input tuned circuit is employed as the aerial couples directly to the source L1 is a low value r f choke which forms the drain load for TR1 and the output from this stage is coupled to the detector via Cl TR2 is the synchronous detector and appears in a grounded base Colpitts circuit which is adjusted by means of VR2 to the point where it is just gent ly oscillating In this state the oscillator will tend to lock onto any similar or very close frequency which in this case is an f m transmission As the input signal deviates around its central frequency the oscillator follows it resulting in fluc tuations in the amplitude of the oscillations and in turn the current consumption of the oscillator cir cuit The oscillator current flows through R4 the RADIO AND ELECTRONICS CONSTRUCTOR Resistors C10 0 1uF type C280 Mullard All fixed values watt 5 C11
5. Fig 1 shows a theoretical latching circuit incorporating three 2 input NAND gates As readers will be aware the output of a 2 input NAND gate is high positive when either both its inputs or only one of its inputs is low negative The NAND gate output goes low only when both its inputs are high In the circuit the output of gate A connects to one input of gate B and to one input of gate C Similarly the output of gate B connects to one input of gate A and one input of gate C whilst the output of gate C connects to one input of gate A and one input of gate B The circuit has three stable states either the output of gate A is low and the outputs of the other two gates are high or the output of gate 658 SUGGESTED CIRCUIT SUGGESTED GROUT 3 WAY TOUCH BUTTONS By G A French B on its own is low or the output of gate C on its own is low The opera tion of the circuit can be readily visualised If for instance the out put of gate B is low so also is one in put of gate A and one input of gate C causing the outputs of gate A and gate C to be high These high out puts connect to the inputs of gate B firmly latching its output in the low condition Similar reasoning will show that gate A output may alter natively be latched in the low con Fig 1 Theoretical circuit in corporating three CMOS NAND gates The circuit has three stable states dition on its own as may the output of gate C Whatever
6. dimmer board to the track At the upper centre edge of the diagram of the copper side of the main clock board is the positive supply track which connects to the positive lead out of C1 and to C3 Make a small break in this track between the connections to these two capacitors The break can be made quite easily with a sharp modelling knife Drill additional holes NL Fig 3 Details of the printed board which is reproduced full size 688 RADIO AND ELECTRONICS CONSTRUCTOR through the track on either side of this break The hole nearer C1 positive lead out provides the positive input to the auto dimmer and the hole nearer C3 takes the auto dimmer positive output This completes the modifications to the main printed board of the clock The board can now be remounted in the case R2 may next be set up although in most in stances it will probably be found satisfactory to simply leave it with its slider at about the centre position of the track The reason is that the most usual requirement of the auto dimmer will be that it should operate when the clock is in virtually total darkness and this will be achieved at almost any setting of R2 It is however possible to adjust R2 so that the display will dim under semi dark con ditions R2 slider should not be turned fully clockwise whereupon minimum resistance is inserted into cir cell being brightly illuminated during the day b sunlight or an electric l
7. By R A Penfold A neat little unit which dims digital clock dis play brightness under dark conditions THE CIRCUIT Fig 1 shows the manner in which the auto dimmer is added to the clock It is connected between the positive output of the clock power supply and the positive input to the clock circuit The Aiea wiee has two output states one where the output voltage is virtually equal to the input voltage and one where the output voltage is at about half this level The former is the normal state of the circuit and the latter occurs when the clock is in almost total darkness It will be apparent that the circuit does not just reduce the voltage supplied to the clock display but it also reduces the operating voltage for the entire clock In practice this does not adversely affect clock operation provided the dimmed output voltage is not made excessively low It may be noted that in Fig 1 the positive supply rail is shown above the negative rail whereas in the clock circuit in last month s issue the positive rail was the lower one The complete circuit of the auto dimmer appears in Fig 2 Here a photoconductive cell type ORP12 is coupled to the input of the Schmitt trigger consisting of TR1 TR2 and their associated components The output of the Schmitt trigger couples to the emitter follower TR3 The circuit is arranged such that TR1 is turned off in the dark condition with its base emitter voltage being below the
8. and TR1 base goes suf If the voltage at TR1 base is caused to go ficiently negative for it to be turned off and the positive a level will be reached at which TR1 com Schmitt trigger to change over to its alternate state mences to pass collector current This will cause The darkness level at which the Schmitt trigger the base current available to TR2 via R3 to be operates is chosen by adjusting R2 reduced whereupon a lower voltage is dropped across R6 This further increases the base CONSTRUCTION emitter voltage of TR1 and a regenerative action takes place which concludes with The auto dimmer is constructed of a small R1 turned fully on and TR2 cut off The printed circuit board and the copper pattern and change of state in the transistors takes place of component layout of this are illustrated actual course in a minute fraction of a second and is triggered when the appropriate voltage is applied to TRI base With TR2 cut off the output voltage of the auto dim circuit is only slightly lower than that on the positive rail The circuit will revert to its previous state if the base of TR1 is taken negative but the voltage at which the changeover occurs will be lower than that at which TR1 was turned on This hysteresis effect is a characteristic of Schmitt trigger operation and is useful here as it ensures that the trigger does not continually change states for very small changes in input potential The output current available fro
9. voltage shown the boosted h t voltage would be of the order of 500 volts b Virtually the same circuit is given the more modern semiconductor version of a typical valve line output stage Smithy pulled Dick s note pad towards him took out a pen and sketched out a circuit on its top page Fig 3 a We haven t got time to go through the whole line output cycle he went on but as we re only interested in the boosted h t supply we need only consider part of it anyway And I need only show you the line output transformer primary winding which produces the boosted h t Now during the latter half of the scan section of the line cycle when the spot is being deflected horizontally across the screen of the picture tube the line output valve is on and is drawing a continually increasing anode current from the positive h t rail through the booster diode and through the line output winding below the cathode of the booster diode Since the lower end of this winding is negative of the booster diode cathode simple transformer action causes the top end of the win ding above the booster diode cathode to be positive The result is that the boosted h t reservoir capacitor charges up causing a voltage which is considerably positive of the h t positive rail to be available on the terminal of the capacitor which connects to the top end of the winding And that s the boosted h t voltage 692
10. 0 015 ae C280 Mallard R1 Iko C12 1004F electrolytic 10V Wkg R2 1k 2 C13 100uF electrolytic 10V Wkg R3 120ka TC1 25pF trimmer type C801 R4 2 2k a R5 18ka Semiconductors R6 10ka TR1 BF244B R7 2202 TR2 BF194 R8 1 2Mo TR3 BC109 R9 4 7kaQ TR4 BC109 R10 2200 D1 BZY88C7V5 Ril 2 7ka D2 BA102 ere sue R14 iko S1 s p s t part of VR2 VR1 ad linear with insulated spindle see text VR2 5kQ log with switch S1 Capacitors Miscellaneous C1 1 8pF ceramic or silvered mica Plastic case 185 by 109 by Cline see text C2 220uF electrolytic 10V Wkg 9 volt battery type PP3 Ever Ready C3 220uF electrolytic 10V Wkg Battery connector C4 0 01pF disc ceramic Telescopic aerial see text C5 4 7pF ceramic Veroboard 0 lin matrix C6 0 0014 F disc ceramic 18 s w g aluminium sheet C7 0 47uF electrolytic 10V Wkg see text 2 control knobs C8 100uF electrolytic 10V Wkg Enamelled wire resistor for L1 L2 see text C9 0 01pF disc ceramic Grommet nuts bolts etc Socket SK1 3 5mm jack socket TR BF 2448 b dgs b c BF 24458 BF 194 BCIO9 Lead outs Lead outs Lead outs Fig 1 The circuit of the single tuned circuit f m receiver Tuning is carried out by VR1 and varicap diode D2 JULY 1978 663 voltage across which varies in sympathy with the oscillator current and these voltage changes then constitute the audio output of the detector Capacitor C4 provides r f fi Enf and decoupling he detector
11. 0 6 volt level required for a silicon transistor to pass collector current TR2 is then made conductive by way of the base current it receives via R3 and R4 10 8 more conventional Schmitt trigger R7 would have a value which is much higher than that of R6 so that the output voltage at TR2 collector would be only slightly positive of the negative rail But in the present application the output voltage needs to fall to only about half that on the positive rail and this re quirement is achieved with the values of R6 and R7 which are specified The resistor values around TR2 are also such that this transistor does not turn hard on when it becomes conductive as is RADIO AND ELECTRONICS CONSTRUCTOR Pos in COMPONENTS Resistors All fixed values 4 watt 5 R1 2 2k0 R2 50k or 47k Q pre set potentiometer 0 25 watt horizontal R3 3 90 Pos out R4 22k 0 R5 12k Q R6 390 Q see text h R7 560 0 TR BCIO9C BC IO9C BCIO9C Neg in BFYSI Semiconductors Lead outs TRI BC109C TR2 BC109C TR3 BFY51 Fig 2 The auto dimmer circuit TR1 and TR2 Photoconductive Cell form a Schmitt trigger which is actuated by the PCC1 ORP12 voltage on TRI base TR3 is an emitter follower feeding the clock circuit Miscellaneous Printed board materials Wire solder etc usual with the more common versions of the at its maximum level If PCC1 is in a dark situa Schmitt trigger tion its resistance is high
12. cant help i its as easy as learning a tune 18 WPM in 4 weeks guaranteed The Complete Course consists of three records as well as instruction books For Complete Course send 5 00 plus part postage 500 overseas surface mail 1 extra Now available Shrouded Morse Keys 2 70 inc UK postage THE MORSE CENTRE Box 8 45 Green Lane Purley Surrey Lenclose 5 00 or large s a e for explanatory booklet 2 metre RECEIVER NR56 fully tunable 144 146 MHz also 11 xtal positions for monitoring specific channels Compact sen sitive ideal for fixed or mobile listening Built in L S 12v DC operation 54 00 inc VAT Crystals if required 2 50 each All popular 2m channels in stock Credit terms available s a e details Marine Band Rx 156 162MHz similar to NR56 59 40 xtals 2 79 Relays 6v coil 25A contacts SP make 800 2P make 90p Neons min wire ena 65p 10 4 100 Slide Switches min DPDT 18p ea 5 14p 2 pole 3 position22p each 5 18p Resistor Kits E12 series 22 Q to IMQ 57 values 5 carbon tilm 4W or W Starter pack 5 each value 285 2 95 Mixed pack 5 each W W 570 5 40 Standard pack 10 each 570 5 40 Giant pack 25 each 1 425 13 25 1 C s new 7410 25p CD4001AE 250 SN76660 75p NE555 55p 723 TOS 75p 709 105 741 DIL 8 Op amps 30p BNC Cable mtg socket 50 2 20p 5 15p PL259 UHF Plug amp Reducer 68p 5 600 50239 UHF Socket panel mtd 55p 5 45p Nicad recharg
13. if you remember we were talking about the flyback rectification bit which as I just pointed out is used in the focus con trol circuit Smithy slowly simmered down And he grated you were right in pointing out that flyback rectification is used there Now let me collect my thoughts Ah yes The associated winding on the line output transformer applies positive going flyback pulses to the rectifier and the following 10uF reservoir capacitor and the resul tant positive voltage then supplies the focus pot the slider of which connects to the focus electrode of the tube The rectified voltage which is around 300 volts also goes to the first anode incidentally The first anode and the focus electrode ROA both draw very small currents and so flyback rectification is quite in order here There s another rectifier remarked Dick and that s at the bottom of the same winding which passes positive going flyback pulses to the focus pot circuit rectifier There s a chassis tap into the win ding in between too Fig 7 And that remarked Smithy ts the scan rectification circuit I referred to right at the beginning From the way that the complete winding is drawn in the diagram you would expect the waveform at its bottom end to be of opposite polarity to that at the top end And so in practice it is This last part of the line output transformer circuit gives scan rectifica
14. is tuned over the f m band by varicap diode D2 which in company with the series trimmer TCi and L2 completes the os cillator tuned circuit R2 and D1 form a zener shunt regulator circuit which provides a stabilized voltage for the 0 pene VR1 The voltage tapped off by VR1 slider is applied to D2 through R3 and the circuit can be set up for a tun ing range of about 88 to 100MHz C7 couples the audio output from the detector to the base of TR3 R7 and C9 provide additional r f filtering and this is necessary since both audio stages have responses which extend into the v h f spectrum Instability could easily result if a significant amount of oscillator signal were to be allowed to enter the audio stages The filter com ponents also provide the necessary de emphasis to the audio signal This de emphasis is merely a small amount of treble attentuation which com pensates for the treble boost pre emphasis applied to the audio signal at the transmitter The purpose of the pre emphasis is to provide an im proved signal to noise ratio Both the audio stages are conventional high gain common emitter circuits R13 the emitter resistor for TR4 is unbypassed and provides a measure of negative feedback in the output stage This reduces what is otherwise a marginally excessive gain and also slightly improves the audio quality Supply decoupling in the various sections of the circuit is provided by C2 C3 C8 R10 and C12 S1 is the on
15. noise over the range of 30 to 200Hz in a duct measuring approximately 300mm square With a fan having a broad noise peak at 160Hz the attenua tion over the range was 14dB The precise attenuation and frequency range of operation is largely govern ed by the need to ensure accurate reproduction of the initial sound field for example 20dB attenua tion corresponds to 90 accuracy in the operation of the loudspeakers Following upon the above interesting news item we express the hope that sound pollution from radios etc will not be a feature of outdoor life this summer The position has certainly improved since the first advent of transistor portables and we can all set a good example PRINTED CIRCUIT BOARDS AVAILABLE Messrs Ramar Constructor Services of Masons Road Stratford on Avon Warwickshire CV37 9NF inform us that they can provide printed circuit boards for the Duette Stereo Amplifier described in our January issue and for the 2 Metre Converter described in our February issue The p c b s for the Duette are priced at 2 45 the pair in cluding VAT and pape The boards being in fibreglass roller T tinned and fully drille _ The p c b for the 2 Metre Converter is produced as a double sided board one side being plain for screening on fibreglass roller tinned and drilled The price is 2 38 including VAT and postage JULY 1978 NEW SCIENTIFIC eo ao 90 00 ec 20 830
16. of energy in the production of semicon ductor components In the manufacture of a semiconductor device a crystal of silicon is first grown at the highest possi ble purity and is then sliced into thin wafers Next precise amounts of an impurity called a dopant are introduced into the wafer to change its elec trical properties and turn it into a semiconductor device with n and p regions In the new process one side of the silicon wafer is heated whilst the opposite side is cooled The temperature difference forces the dopant in the form of a droplet of liquid to migrate through the wafer from the cooler side to the hotter side The thermomigration technique can be ac complished in minutes By contrast the best previous commercial method for equivalent doping of wafers requires nearly a week of processing time Also the new process can be performed at a temperature several hundred degrees Fahrenheit below that required up to now With established techniques excessive wafer breakage is often a problem because shallow do pant penetration of around two to three thousandths of an inch necessitates the use of cor respondingly thin wafers With the new approach it is possible by manipulating wafer alignment and temperature to control the size shape and concen tration of doped regions in the wafer The end result of this new technology can be the creation of whole new classes of semiconductor devices which never existed bef
17. off With a sigh Smithy got up from his stool and walked over to Dick s bench Show me Dick demonstrated the behaviour of the receiver Smithy watched unimpressed when the screen came Testmeter Brightness contro a momentarily to life as Dick switch ed the set off There s nothing very com plicated there he commented I should look for a snag in the brightness control circuit In fact I should check the brightness control potentiometer itself Perhaps there s an open circuit between one end of the track and its tag You can do a simple d c ohms test there With which words Smithy stumped back to his music centre Deflated Dick took the television set plug from its mains socket removed the back of the receiver and after manipulation of the printed board found himself able to reach the tags of the brightness potentiometer He switched his testmeter to an ohms range and applied its test clips to two of the potentiometer tags Fig 1 a b Fig 1 a Following Smithy s bidding Dick checked the continuity of the brightness control potentiometer track in his faulty monochrome TV receiver b When he checked between the slider and the track tag when the control was turned fully clockwise he found an open circuit between the track end and the tag RADIO AND ELECTRONICS CONSTRUCTOR From video output stage 25V 220urF 1 5V Us Fr
18. on which are assembled the input Schmitt trigger and prescaler stages The board is reproduced full size CONSTRUCTION Nearly all the components are mounted on four printed circuit boards One board contains the in put and prescaler circuitry whilst the others are for the mains power supply the counter divider chain circuits and the l e d displays Details of the input circuit and prescaler printed circuit board are shown in Fig 4 This shows both the component layout of the board and the copper backing pattern The diagram is reproduced actual size so that it can be easily copied This board like the other three which will be described later is fairly complex but it is not difficult to produce if a p c b etch resist pen having a fine point is available The two mounting holes are drilled for 6BA clearance 678 DISPLAY AND DIVIDERS The circuit diagram of the oseillator divider chain counter and display sections of the unit is shown in Fig 5 TR8 is the crystal oscillator and this uses the well known Pierce configuration C11 enables the oscillator frequency to be trimmed to within less than 1Hz of the nominal crystal fre quency TR9 is a buffer stage and this is a straight forward common emitter amplifier The six 4017 integrated circuits IC3 to IC9 in clusive form the 1MHz divider chain The input signal is applied to the clock input pin 14 of each device and the divided output 1s obtained from pin 12 Th
19. stage And the line output stage with its transformer acts like a veritable power house It knocks out a boosted supply voltage of around 25 volts for the i f stages and some of the video circuitry it produces an e h t voltage of about 11kV for the final anode of the tube it generates some 300 volts for the tube first anode and the focus potentiometer and finally it gives 95 volts for the video output tran sistor and the brightness control cir cuit That s not bad going for just one stage PI say it isn t agreed Dick Stap me Smithy I ve just noticed another diode There s a tap in that last winding we dealt with and it connects via a 4 700pF capacitor and a 100kQ resistor to this diode It also goes by way of a 0 1pF capacitor to another part of the cir cuit Blimey there s no end to the JULY 1978 external circuits which are tacked on to this line output transformer Fig 8 That last diode chuckled Smithy as he glanced down at the service manual is in the line blanking circuit and it clamps the waveform with positive going scan pulses so that the most positive parts are held at chassis potential The result is that the grid of the tube is at chassis potential during the scan period and then goes negative during the flyback period causing the tube to be cut off during that period And the waveform passed via the 0 1pF capacitor goes back to the line flywheel sync dio
20. wire wound around the riddle third of the rod in a single layer The turns should be spaced as closely together as possible If it is found that the length of the winding is slightly different from the 3in shown in Fig 2 so that it is not fully central on the rod this is not of impor tance Bands of insulating tape are used to hold the lead out wires in position and to thus prevent the winding from springing apart The lead out wires 654 are cut to about 50mm in length and then the enamel insulation is scraped off the ends of these leads so that they can be tinned with solder If difficulty is experienced in obtaining tin ferrite rod it is in order to use the more readily available rod having a diameter of 8mm This is cut down from a longer piece in the same manner as the tin rod and the winding has the same number of turns There is just sufficient room in the layout for 8mm rod CONSTRUCTION Most of the components are assembled on a 0 110 matrix Veroboard panel which has 14 holes by 7 copper strips The component layout of this panel is shown in Fig 3 Start by cutting out a panel of the required size using a small hacksaw and then make the single break in the copper strips No mounting holes are drilled in the board Then solder the components into position Note that R2 is a skeleton poten tiometer having 0 2in spacing between track tags and 0 4in spacing between track and slider tags The general arrangem
21. 20 os The student market is particularly well catered for with the introduction of Commodore s new scientific calculator which represents a breakthrough in calculator features price odel SR4912 is an 8 2 digit LED calculator and undoubtedly represents fine value in students scientific models At a price of 12 50 it features 50 key functions including log and trig mean and stan dard deviation polar rectangular con version and many more power keys Ea een UDALL For a different view of the weather see page 684 657 The current availability of CMOS digital i c s makes it possi ble to make up a number of simple logic circuits which would be relativel difficult to bring into practical operation with the earlier t t l devices Also CMOS i c s have the advantages of not requiring a regulated power supply and of hav ing symmetrical input and output switching from high to low voltages and vice versa exceptionally low current consumption and virtually infinite gate input resistance On the debit side is the fact that many CMOS gates have a low output current capability with the result that external discrete transistors are required if a CMOS device is to control a load having a current re quirement in excess of a few milliamps The circuit to be described in this month s Suggested Circuit article highlights both these advantages and the disadvantage LATCHING CIRCUIT
22. 661 SINGLE TUNED CIRCUIT F M RECEIVER By P R Arthur Local Station v h f receiver using the synchronous detector principle Simple v h f broadcast receivers can make an interesting alternative to the more usual a m receiver project They provide good quality relatively interference free reception of B B C and commercial stations in areas of reasonably good signal strength The main disadvantage of a simple v h f set is that it is not really suitable for use in mediocre or poor reception areas A simple v h f detector can be very sensitive but tuning and ad justment become excessively critical on very weak nes and there is a marked loss of audio quality The prototype is used approximately 25 miles away from the B B C Wrotham transmitter and excellent results are obtained The receiver uses four transistors including a Jugfet and it provides an output which is suitable for high impedance headphones or a crystal ear piece In fact it will even drive any reasonably sen sitive pair of low or medium impedance headphones The set has a telescopic aerial and is powered from an internal PP3 battery It is thus completely self contained This is not intended to be a miniature pocket type receiver and the unit is built into a case which measures approximately 185 by 109 by 60mm This coupled with the use of varicap diode tuning enables good freedom from hand capacitance effects to be obtained 662 THE CIRCUIT
23. Hz minimum with a minimum resolution of 10Hz The accuracy of the unit is largely dependent upon the adjustment of the clock oscillator and should be within 0 1 The unit is quite sensitive and at middle frequencies requires an input level of only about 20mV r m s However the sensitivity does fall away somewhat towards the upper and lower limits of the operating range Digital frequency meters tend to be rather com plicated instruments and although this particular unit has been designed to be as simple as possible without sacrificing accuracy or sensitivity it is still quite an involved project which is only suitable for the more experienced constructor The circuitry is largely based on eleven CMOS i c s but three other i c s and ten transistors are also employed in the unit An r f signal generator is required for checking and adjusting the meter after it has been completed BASIC PRINCIPLE The manner in which a digital frequency meter operates is very simple In fact in this respect it is probably the most simple form of frequency meter The block diagram of Fig 1 shows the basic arrangement Fig 1 The basic form of a digital frequency meter The enabling gate is held closed for a pre determined period and the counter then dis plays the number of input signal cycles which have passed through 672 Input signat o The input frequency is displayed on an elec tronic counter which shows the answer in or
24. O oO oO O O O 8 Battery clip Fig 2 The wiring of the receiver Nearly all the parts are assembled on the Veroboard panel spaced out over this length he coil ends are scraped clean of enamel and tinned before being soldered to the appropriate strips of the Veroboard The Veroboard panel is initially cut to size by means of a small hacksaw and the two mounting holes are next drilled 6BA clear The 8 breaks in the copper strips are then made after which the board components are mounted and soldered in position Note that C4 and C5 are mounted on the copper side of the panel Their lead out wires should be kept as short as possible Those of C4 are covered with sleeving to prevent short circuits to JULY 1978 the copper strips over which they pass In fact the lead out wires of all components in the r f cir cuitry should be no longer than is reasonably necessary CASE LAYOUT The photographs help to show the general layout inside the case and it is strongly recommended that this is not radically altered in any way In this application the lid of the case becomes the rear panel with the controls output socket and aerial appearing at the upper face VR1 can be mounted 665 Detail illustrating the Veroboard assembly more closely The board was not bolted to the case when this shot woe tekon direct to this upper face but greater freedom from hand capacitance effects will be given if it is a type
25. OUDSPEAKERS By Martin Colloms 246 pages 215 x 135mm 84 x 5310 Published by Pentech Press Limited Price 8 95 The development of high fidelity loudspeakers has resulted in considerable improvements in per formance over the last decade and this book deals with these as well as with virtually all other aspects of modern high quality loudspeakers and their enclosures It hardly needs to be stated that in the high fidelity chain of reproduction the loudspeaker is the component which is most dependent on subjective evaluation although it is possible nowadays for much of a loudspeaker s functioning to be judged by objective analysis and measurement After angeneral review the book deals with theoretical aspects of diaphragm radiators practical diaphragms acoustic loading low frequency system analysis moving coil direct drive radiators crossover systems enclosures and the assessment of loudspeaker performance Each chapter is followed by an extensive listing of references and the book takes in work originating in the U S A Japan and Australia as well as in the U K The book will appeal to a wide range of readers from do it yourself enthusiasts to students of electronics and is written at a depth which will make it of valu to professiona loudspeaker designers studio engineers and technica writers on hi fi subjects There is a minimum of mathematics and the work clearly reflects the author s personal involvement in practical loudspea
26. R AND C VALUES By R D Smith Combining two E12 resistors or capacitors to obtain round number decimal values We occasionally require resistance and capacitance values which are in the decimal series of 10 20 30 40 50 60 70 80 and 90 and it can be a little frustrating when we find that the only com ponents we have on hand or can purchase have values in the preferred E12 series This you will recall runs in the following manner 10 12 15 18 22 27 33 39 47 56 68 and 82 There is no provi sion for the decimal values of 20 to 90 If however we are pre ared to use two E12 resistors in parallel or two E12 capacitors in series we can readily make up com inations which calculate precisely at a decimal value or which calculate at the decimal value with an error of 0 5 or less PARALLEL R SERIES C The total value of two resistors in parallel as in Fig 1 is R1 x R2 Ri R2 where R1 and R2 are the values of the individual resistors DANTIN AND ET RECTRONICS CONSTRUCTOR Fig 1 Two resistors connected in parallel Total resistance Cy C2 Fig 2 A series combination of two capacitors Total capacitance TABLE The Table shows how two E12 values of parallel resistance or series capacitance can be combined to give total values in the decimal series Two of the entries are glaringly obvious 100 and 100 must give 50 and 180 and 180 must give 90 Not quite so Parallel R or Total
27. TIONS By J Brian Dance 96 pages 215 x 135mm 84 x 4310 Published by Newnes Technical Books Price 2 25 In terms of time it is not so long ago when one of the first integrated circuit operational amplifiers the 702 was introduced to the electronic scene This was in 1965 and the 702 was soon followed in 1965 66 by the immensely successful 709 But 13 years is a very extended period so far as the exuberant field of integrated circuit development is concerned and the present day user of i c operational amplifiers can choose from a wide range of monolithic devices each hav ing its own individual characteristics Mr Dance s book deals with current op amps in an uncomplicated and very informative style The approach is non mathematical and there are numerous circuits complete with component values The first part of the book covers operational amplifier basics in terms of the 741 which is inex pensive is easy to experiment with and readily demonstrates operational amplifier principles Other integrated circuit op amps are then dealt with as also is frequency compensation The book then turns to devices with f e t inputs audio power circuits and low noise audio pre amplifiers These are followed by a glossary and a good index The book will be of excellent value to anyone who is commencing work with operational amplifiers and will appeal in particular to the non academic technician and the home constructor HIGH PERFORMANCE L
28. Value obvious at first sight perhaps is that 100 and 150 Series C give exactly 60 It is a minor matter of mathematical moment that 22 and 220 give precisely 20 and that 33 and 22 and 220 330 give precisely 30 The remaining values are not quite so exact 47 and 270 give 40 0 to three signifi 33 and 330 cant figures the calculated value working out at 40 03 82 and 470 work out to 69 8 instead of 70 47 and 270 precisely the error is 2 out of 700 or two sevenths of 1 100 and 390 are the worst these calculating out to 79 6 Compared with 80 this represents an 100 and 100 error of 4 out of 800 or one half of 1 In practice not too much to worry about 100 and 150 Lets try out the Table with a few examples If we want a 4 0kQ resistance we may use a 4 7kQ 82 and 470 resistor in parallel with a 27kQ resistor If we want a 30pF capacitance we can connect in series a 100 and 390 33pF capacitor and a 330pF capacitor Another ex ample an 800Q resistance is conveniently given 180 and 180 by the parallel combination of a 1k resistor and an a 3 9k f resistor You may find it convenient to cut out or copy out the Table and put it up on the wall of your workroom It could save you quite a little head scratching in the future particularly with the more awkward combined decimal values of 20 30 40 70 and 80 JULY 1978 669 RECENT PUBLICATIONS Hi IN OP AMPS THEIR PRINCIPLES AND APPLICA
29. aida The Radio amp Electronics Constructor is printed RADIO ELEGTRONIGS CONSTRUCTOR CORDLESS HEADPHONE RECEIVER by A P Roberts NEWS AND COMMENT 3 WAY TOUCH BUTTONS Suggested Circuit by G A French ULTRASOUND DISPLAY SYSTEM by Michael Lorant SINGLE TUNED CIRCUIT F M RECEIVER by P R Arthur DECIMAL R AND C VALUES by R D Smith RECENT PUBLICATIONS CMOS DIGITAL FREQUENCY METER Part 1 2 parts by R A Penfold THERMOMIGRATION by Michael Lorant SHORT WAVE NEWS For DX Listeners by Frank A Baldwin WATCH THE WEATHER by T F Weatherley CLOCK AUTO DIMMER by R A Penfold BOOK REVIEW SCAN AND FLYBACK RECTIFICATION In Your Workshop RADIO TOPICS by Recorder ELECTRONICS DATA No 35 THE AUGUST ISSUE WILL BE PUBLISHED ON 3rd JULY For The Beginner Simple Measuring Bridges 652 656 658 661 662 668 670 672 681 682 684 686 689 690 696 641 RECEIVER By A P Roberts CORDLESS HEADPHONE A unique design mounting the electronics onto the headphones Case only 23 x 2 x 1 in app No trailing wires Although initially designed and built for its novelty value this receiver does have advantages over sets which feed a pair of headphones or an earphone in the conventional way This little set differs from convention in that the electronics are built into the headphones or perhaps it would be more accurate to say
30. amp This is because the cell will then exhibit an extremely low resistance giv ing a slight risk of excessive current flow in the potentiometer track The risk disappears if the potentiometer adjustment is such that it always in serts about 5k or more of resistance into circuits 5k Q is of course just one tenth of the total track resistance If desired it is possible to vary the dimmed dis play brightness to some extent by altering the value of R6 Raising its value will cause an increase in brightness and reducing it will have the opposite effect Its value should not however be increased to more than 4709 or reduced to less than 300 2 TR3 will run rather warm but there is no need to fit it with a heatsink even if the clock circuit has been modified to provide an increased display current as was described at the end of the article cuit if there is a possibility of the photoconductive on the clock a BOOK REVIEW TEST EQUIPMENT FOR THE RADIO AMATEUR Second Edition By H L Gibson C Eng M I E E G2BUP 151 pages 245 x 185mm 93 x 710 Published by Radio Society of Great Britain Price 3 75 The amateur radio transmitting enthusiast requires basic test equipment not only for servicing but also to ensure that he is satisfying his licence conditions Further test equipment is desirable and much of this can be home constructed with a corresponding saving of cost and increase in ex perience The book under review gi
31. anel can be wired up to the rest of the unit The panel fits into the space in the centre of the case The headphone lead is cut down to only about 5in or so in length and then it is soldered into the cir cuit Only two of the three wires in the headphone Battery pos Battery neg Fig 3 Most of the components are wired up on a small Veroboard panel employing the layout shown here cable are actually connected the common lead be ing ignored It is possible to determine which lead is the common one by inspecting the wiring at the jack plug The common lead is the one which con nects to the main part of the barrel of the plug and it is usually colour coded black Constructors who prefer to check out the receiver before cutting the JULY 1978 PPA dil ALLL ASERI ZALEA LEARE 000020 headphone lead may initially make temporary con nections from the board to its jack plug The wire may then be cut and finally fitted after tests have been completed The battery leads are terminated in 6BA solder tags and these are held against the appropriate battery terminals with the aid of a rubber band Take care to ensure that the cell is connected with correct polarity The cell terminals will be marked with their respective polarities The lid of the case must be drilled with a in diameter hole through which the trimmer converter shaft can pass The case lid can then be screwed into position and the trimmer co
32. apacitance and in ductance of capacitance and resistance or inductance and resistance When we combine capacitance and inductance we have of course a tuned circuit Capacitance and resistance can be directly related to time because we ean make up oscillators which are dependent upon the time taken for a capacitor to charge or discharge via a resistor to a specific voltage Notable examples here are the two transistor symmetrical mul tivibrator and circuits incor porating the 555 timer i c It is a lot more difficult to give an example of timing control by inductance and resistance so far as generating an alternating voltage is concerned because it is impossible in practice to obtain inductance on its own without self capacitance stealing onto the scene A blocking oscillator incorporating an iron cored transformer is a rough approxima tion to frequency control by means of inductance and the inevitable resistance in the inductance and the inductance of a TV line output transformer and the line scanning coils certainly controls the timing of a line output stage during the scanning section of the line output cycle Perhaps the most fascinating of time controlling circuits are those employing capacitance and resistance because it is so easy to select the timing by choice of capacitance value If you haven t got an oscilloscope available and vou want to see the waveform given by say a 555 oscillator you can simply
33. atters switch S3 should be suitable for switching mains voltages The horizontal skeleton potentiometer R9 should be a type having 0 2 in spacing between track tags and 0 4 in spacing between track and slider tags The 18 s w g aluminium sheet is used for making a chassis a bracket and a heat sink and details of these will be given next month To be concluded THERMOMIGRATION by Michael Lorant Dr Thomas R Anthony and Dr Harvey E Cline staff research scientists of General Electric Research and Development Centre Schenectady N Y have developed an entirely new technique called Thermomigration which reduces the time required to fabricate a semiconductor device by as COLD Migrating Droplet Radiant Heat Source This drawing demonstrates General Electric s Thermomigration process Droplets of do pant in the silicon wafer migrate from the cold side of the slice towards the hot side taking one thousandth of the time needed to the in troduction of dopants with previous techniques New doping process could herald a fantastic ad vance in semiconductor manufacture much as a thousandfold In addition the novel technique which relies on a temperature gradient to drive a liquid dopant through a silicon wafer reduces fabrication temperatures and increases processing yields The patented innovation is also expected to result in another important by product a signifi cant saving
34. b s father the late Richard Arbib The Hong Kong exhibition attracted exhibits from 120 British Companies RADIO AND ELECTRONICS CONSTRUCTOR COMMENT ADDING SOUND TO CANCEL NOISE One of the problems of working in industrial environments is that of noise and the usual approach towards obtaining a reduction in this particular field of audio pollu tion has been the use of sound roofing materials baffling and the ike Plus of course attempts to reduce the level of noise generated at the source itself All such devices are of a passive nature and it is of considerable in terest to learn from the National Research Development Corpora tion of 51609 to reduce noise by an active method A further noise is added to the original noise and achieves partial cancellation of it To date the technique has only been developed to the state where noise at low frequencies can be dealt with The work carried out has been on the low frequency noise from gas turbines which have presented what has always up to now seemed to be an insoluble problem However recent research at Chelsea Collen into a system devis ed by Dr M A Swinbanks suggests that the answer may lie in absor bing sound by generating additional sound to intorters with and cancel the offending frequencies Work on the Swinbanks system is currently being financed by the National Research Development Corporation and at the pre
35. des The important parts of the waveform in this case are the negative going flyback pulses These make the flywheel sync diodes conductive but I don t in tend to start digging into that part of the circuit now Especially as the only thing that started off this par ticular gen session was a faulty brightness control pot Well said Dick you ve cer tainly opened my eyes so far as the line output stage of this set is con cerned It s a very busy little stage isn t it It certainly is replied Smithy Which reminds me that it s time that I became busy too and got back to my work instead of spen ding my time nattering away like this Still it s nice to have a little break from work every now and again I suppose so conceded Smithy provided it doesn t happen too often With us grinned Dick it only happens once a month a MORSE MADE EASY BY THE RHYTHM METHOD These courses which have been sold for over 23 years have been proved many times to be the fastest method of learning Morse You start right away by learning the sounds of the various letters numbers etc as you will in fact use them Nota series of dots and dashes which later you will have to translate into letters and words Using scientifically prepared 3 speed records you automatically learn to recognise the code RHYTHM without translating You
36. dinary denary form There are several types of digital dis play which can be used in this application and the type actually used here are seven segment l e d displays The functioning of these displays has been described a number of times in previous issues of this journal and so need not be considered further here hi the present unit a four digit display is employed An electronic switch operating as an enabling gate appents at the input of the counter and this only allows the input signal to pass the counter when a suitable pulse is applied to a second input of the gate A precision pulse generator feeds this second input and it is the length of the pulse that this generates which determines the range of measurement provided by the unit If for example the length of the pulse is 1 second then a four digit counter will operate as a 0 to 9 999kHz frequency meter A little consideration will show that this is the case If the input signal were 1kHz then 1 000 input signal pulses would be fed to the counter dur ing the 1 second period The counter will then dis play 1 000Hz or 1 000kHz according to the position of its decimal point It follows that the maximum frequency which can be measured is 9 999kHz as any frequency higher than this will cause the counter to overflow Higher ranges can be provided by using shorter gate enable pulses A gate time of 100 milliseconds or 0 1 second would increase the range to a max Electronic
37. dule is from 1000 to 0300 and the power is 1kW AROUND ODEI TAL ISRAEL Jerusalem on 21500 at 1220 pops commercials in English identification announcements and into French at 1230 Announced to Western Europe and 682 North America in parallel on 11655 15405 and 17815 and to Asia on 15570 E GERMANY Berlin on 21540 at 1241 OM with an nouncements and identification at the end of the English programme to South East Asia Announced in parallel on 15115 and 17880 SOUTH AFRICA Johannesburg on 21535 at 1356 programme in English about crocodile conservation identifica tion and time check at 1400 followed by a local newscast Announced in parallel on 11900 and 15220 NORWAY Oslo on 21730 at 1405 OM and YL with a talk about Norwegian affairs in English Identification at 1411 EGYPT Cairo on 17670 at 1419 local type music YL and OM in Arabic in the Domestic Service General Programme scheduled from 1300 to 1830 on this channel with programmes intended for the Arab World East and Central Africa and Southern Europe PORTUGAL Lisbon on 17895 at 1608 YL with news of Por tuguese affairs in the English programme directed to the Middle East scheduled from 1600 to 1630 not Sundays Lisbon on 9740 at 2030 OM with identification followed by the news in English for Europe scheduled from 2030 to 2100 English programme and in parallel on 6025 TURKEY Ankara on 9515 at 2132 OM with a local ne
38. e As you ve already mentioned said Smithy it supplies the extra high tension voltage for the final anode of the picture tube In this particular circuit the e h t is provided by its own separate win ding Since the current drawn by the final anode is quite small being about a tenth of a milliamp or so the winding is connected so that it feeds positive going flyback pulses to the e h t rectifier The conse quent e h t voltage with this set is then about 11kV Fig 4 Flyback pulses I can un derstand complained Dick frow ning Just now though you were talking about scan pulses Ah ves said Smithy picking up his pen again Well let s next take a look at the voltage which is induced in that e h t winding It will have a waveshape something like this with spaced out high voltage pulses appearing at flyback and long comparatively flat sections between these pulses The average voltage of the waveform will be just slightly above the flat sections which represent the scenning part of the line output waveform during HRV Fig 4 The e h t section of the line output stage In most receivers the e h t reservoir capacitor is given by the capacitance between the inside and outside graphite coatings of the picture tube In this receiver a 1 000pF capacitor is added in parallel RADIO AND ELECTRONICS CONSTRUCTOR Average voltage a lie Flyback a
39. e clock enable pin 13 and reset pin 15 ter minals of each i c are simply taken to the negative supply rail and the ten unused outputs are ig RADIO AND ELECTRONICS CONSTRUCTOR Aci THVIGG 66 ZHW666 6 8 dig Z2H46 666 2H166 66 5300 0007 90440 LOIDE 9 1 POWO 6 8 Z 0004102 6 04102 6078 JULY 1978 nored with no connections made to their pins Sl a b is the range switch and this connects the output of the appropriate 4017 divider to the 4017 pulse generator IC9 The manner in which IC9 produces the control pulse has already been discussed and go will not be considered further here The common emitter amplifier TR10 func tions as an inverter stage R24 limits its base current to a safe value and C15 is a speed up capacitor It is essential that S1 a b is a break before make type If a make before break switch were employed two of the divider i c outputs would be briefly short circuited together when changing from one range to the next Since the outputs could well be at opposite logic states when this occurs there would be a high risk of damage to the i c s concerned Break before make rotary switches are currently listed by Maplin Electronic Supplies and the type employed should be a 3 pole 4 way ow with connections made to only two of the poles The 4026 decoder driver i c s can drive the seven segment l e d displays directly and there is no need to use outpu
40. e dis covered something here If we turn the waveform upside down so that the scan sections are positive going and then apply this to the rectifier we ll also get a positive rectified voltage output The positive input to the rectifier will be present near ly all the time too won t it That is to say not spaced out like the flyback pulses are This means that the rectified output will be much better regulated and will be able to supply quite a high current with only a small value of reservoir capacitor You re exactly right Am I Gosh To use the usual terms con tinued Smithy you can get a much higher rectified output current from scan rectification than you can from flyback rectification But there s a snag When isn t there Can you asked Smithy gently see it Let me think about it said Dick Now when we have flyback rectification the peak rectified positive voltage will be the voltage by which the flyback peaks go positive of the waveform average voltage I think that s right isn t it 3 Apart from the very small forward voltage dropped in the rec tifier which can be ignored here you re completely right Good said Dick encouraged Then when we use scan rectifica tion the peak rectified voltage is the maximum amount by which the scan part of the waveform goes positive of the average voltage For a given line output tra
41. e only one decoupling component is used this being C16 RADIO AND ELECTRONICS CONSTRUCTOR NEXT MONTH In next month s concluding article we shall carry on to the construction of the printed board on which is assembled the circuitry of Fig 5 For convenience a full Components List accom panies this article although it will be appreciated that the functions of some components will not be fully apparent until they are dealt with in the con structional details to be given in next month s issue Nevertheless some notes on the components here will be of value The availability of the semiconductors has already been dealt with The mains transformer employed in the unit is the type M1N TR 15V retailed by Maplin Electronic Supplies The 1MHz crystal and holder are available from several out lets The display filter is an optical filter suitable for red displays and that employed by the autnor was the Electrovalue type PNF21 The author s frequency meter was assembled in a Veropak case type 49 1470L which has dimensions of 11 by 4 4 by 8 6 in This has a p v c clad steel shell and an anodised aluminium front panel and should be available from stockists of Vero cases or from Retail Depart ment Vero Electronics Ltd Industrial Estate Chandlers Ford Hants SO5 3ZR Other metal cases of the same dimensions or larger may also be used The DL704 displays can be obtained from Ambit International Dealing with smaller m
42. e temperatures and it is therefore particularly suitable for small castings The mixture will cure fully at 25 C in 24 to 36 hours but will cure in as little as 3 hours at 60 C Once mixed the system has a life at 25 C of about 2 to 3 hours Further details on the 200 gram sachets may be obtained from Ciba Geigy Plastics and Additives Com pany Plastics Division Duxford Cambridge CB2 4QA DOING TIME Although we do not always pay much attention to the fact as soon as we change in any electrical or electronic work from direct voltage and current to alternating voltage and current we are introducing a completely new dimension All alternating quantities whether they be the u h f television signal you pick up on the roof top aerial the audio output from a hi fi amplifier or the mains supply which is brought to us by courtesy of the Central Electricity Generating Board are precisely defined in terms of time It may be that the time element becomes partly hidden because virtually all the measurements are expressed as the number of cycles which exist within the fixed period of 1 second The change of terminology from cycles per second to Hertz may also be responsible for shifting the time concept one layer lower in our thinking We can control the timing of elec tronic circuits by mechanical means as with a quartz crystal or hy purely electronic means In the latter case we take advantage of the properties of c
43. eables phy sically equiv to zinc carbon types AAA U16 1 64 AA U7 1 15 C U11 3 15 D U2 4 94 PP3 5 20 Any 5 less 10 Any 10 less 20 We stock amateur V H F equipment and mobile aerials s a e details Distributors for J H Associates Ltd switches and lamps PRICES INCLUDE UK POST PACKING amp VAT Mail order only Sole Address GAREX ELECTRONICS 7 NORVIC ROAD MARSWOATH TRING HERTS HP23 4LS Cheddington STD 0296 668684 695 ARALDITE PACKS I should imagine that few readers will require an introduction to that excellent adhesive Araldite In the Recorder household for instance this epoxy resin has been used for many jobs ranging from the moun ting of radio components on a chassis to the successful blocking of holes in of all things an enamel bucket In industry Araldite is widely employed for the potting of components and small electronic assemblies And it is made up by combining the requisite amounts of resin and hardener Araldite has been available in two part sachets containing 500 grams of the material for industrial potting applications and the manufacturer now announces the introduction of smaller 200 gram sachets These should be of special interest to users who need to employ potting resins only occasionally or whose applications do not merit the use of an automatic metering machine to obtain the correct mix ture of resin and hardener The 200 gram
44. ements in Portuguese OM with ballad Schedule is from 0800 to 0330 and the power is 1kW Radio Ribamar Maranhao on 4785 at 0126 folk music and songs identification by OM at 0130 The schedule of this one is from 1100 to 0400 and the power is 5kW Radio Borborema Campina Grande on 50285 at 0210 OM in Portuguese several mentions of Campina Grande Schedule is from 0830 to 0500 and the power is 1kW sometimes wanders down to 5023 and or identifies as A Princesa do Sul Emisora Rural Santarem on 4765 at 0238 local style music Jove song by OM in Portuguese quite a torried affair I gathered The schedule is from 0830 to 0400 and the power is 5kW te WORLD RADIO TV HANDBOOK i There must be many readers of these columns who would like to know more about the world of short wave listening and the short wave stationg mentioned here month by month but do not know where to obtain such information It is to this type of reader that the following review is presented The 1978 issue 32nd Edition of the World Radio TV Handbook comprises 512 pages packed with facts figures and information about short wave stations frequencies schedules interval signals addresses callsigns powers and per sonalities Quite apart from complete details of Long and Medium wave stations and TV transmitters there is also a wealth of information about such matters as DX programmes of the world maps complete with time co
45. ence both in puts of gate B go high and its output goes low When the negative con nection is taken from point X gate B output is low and remains low with the other two outputs high Note that the output of gate B is not forced low by the negative connec RADIO AND ELECTRONICS CONSTRUCTOR VoD nection causes both its inputs to be high by way of the other two gates whereupon its output goes low following standard NAND gate principles In practice the negative connection to point Y may be of a momentary nature only If we next want to make the low output that of gate A we momentarily apply the nerakve connection to point X Subsequently applying the negative connection to point Z will then make the output of gate C go low Should we apply the negative con nection to say point X when the output of gate A is already low nothing happens both ends of the associated current limiting resistor are at the same potential and the circuit state is unaltered The circuit of Fig 2 can be made to operate with t t l gates but the choice of current limiting resistor value is rather critical if we are to ensure that gate output current ratings are not exceeded and that gate input current requirements are satisfied Also the presence of resistors between one gate output and the input of another gate means that the circuit is not operating to proper t t l standards None of these difficulties is present with CMOS gates The fact tha
46. ent of the receiver can be seen from the accompanying photographs A Verobox type 75 1469 L is used as a housing and as the receiver has been designed to fit into this case it is probably best not to attempt to use an alternative The ferrite aerial is glued in position at the top of the case using a good gap filling adhesive such as an epoxy type The HP7 cell fits into the space op posite this at the bottom of the case A 250pF mica compression trimmer is used as the tuning capacitor and this is fitted with a trimmer con verter which replaces the adjusting screw and has a tin shaft for a knob The trimmer and the trimmer converter are available from Home Radio Components Ltd The tuning capacitor is mounted on the extreme right hand side of the case and its two tags must be bent forwards slightly so that they are not obstructed by the ferrite aerial The tuning capacitor is mounted by the bush and nut which are situated at the rear of this component It does not matter which way round the connections are sa to the tuning capacitor and to the ferrite aerial RADIO AND ELECTRONICS CONSTRUCTO i i i H S1 is mounted towards the top of the left hand side panel of the case and it is important that this be a sub miniature toggle switch as there is very lit tle space to adai it An entrance hole for the headphone lead is made in the side of the case just below S1 When all this has been completed the component p
47. er from the mains or from a 12 volt battery If you con nect a battery to it the battery voltage passes to a stabilizing cir cuit which provides a regulated out put of around 11 5 volts And when you connect the mains to it the mains is passed to a step down transformer and a rectifier and smoothing circuit the output of which also goes to the stabilizing cir cuit So whether it s mains or battery operated the set still has to work with a supply of only 11 5 volts BOOSTED H T SUPPLY Humph grunted Dick Well let s go back to the ordinary type of TV where the power supply is ob tained direct from the mains What extra job does the line output transformer do in these sets It provides boosted h t replied Smithy promptly The simplest example here is given with the earlier sets having line output valves rather than line output tran sistors because the circuitry is a lit tle easier to understand Here s part 691 Boosted HT 200V Boost reservoir approx capacitor Wl i HI it Part of line output H transtormer 11 11 11 Line output valve a 25V boosted Boost voltage reservoir capacitor 11 5V Part of line output iH transformer Line output transistor 6 Fig 3 a A look at one of the earlier valve line output stages readi ly demonstrates the formation of a boosted h t voltage With the h t
48. ful constructional infor mation 685 This device has been designed primarily as an add on unit for the Single I C Digital Clock which was described in last month s issue Some digital clock i c s have an auto dim facility built in so that very few external discrete components are required to add this feature However such is not the case with the AY 5 1224A device which is employed in the Single I C Digital Clock as this i c was chosen to cater for a good and very simple basic clock design _ The auto dimmer circuit to be described is quite simple and can easily be added to the clock with a minimum of modification to its design The ex perienced constructor could probably adapt the circuit to operate with similar clocks incorporating the AY 5 1224A but this has not been checked by the author and should not be attempted by anyone who is not fully competent The purpose of the auto dimmer is to reduce the brightness of the display under very dark con ditions Under such conditions the display can become a little difficult to read due to glare and the facility is especially useful if the clock is to be used in a bedroom o Pos CIC pin 2 Output to clock Neg Neg 0 ss 1C pin 5 Fig 1 How the auto dimmer unit functions It takes up the positive and negative outputs of the clock power supply and then varies the positive supply voltage fed to the clock itself 686 CLOCK UTO DIMMER
49. further in the clockwise direction than is ab solutely necessary as this would cause a needless degradation of performance R2 should be set up with a new HP7 cell connected 655 NEWS ANALOGUE MAGNETIC TAPE RECORDER LOGS VITAL DATA IN SEA WAVE ENERGY RESEARCH An EMI Technology high performance magnetic tape recorder is playing an important role in the Department of Energy s continuing R amp D programme for winning power from the waves around Britain s coast One of their portable SE7000 analogue instrumentation recorders is be ing used with equipment provided by The National Maritime Institute NMI and the British Hover craft Corporation for experiments being under taken in the Solent by Wavepower Ltd a company comprising Sir Christopher Cockerell inventor of the Hovercraft and E W H Gifford and Partners consulting engineers The Wavepower project is concerned with evaluating the effectiveness of the Cockerell Con touring Rafts see diagram These have a series of hydraulic motors pumps situated between each raft in order to convert the energy of the raft mo tion into high pressure in a fluid Initially trials of ath scale raft strings were conducted by the British Hovercraft Corporation in test tanks on the Isle of Wight and now th scale trials are being held at sea in the Solent The recorder is being used to monitor a number of critical parameters relating to the design ef ficiency and s
50. gate output is low the remaining two gate outputs are high reinforcing as it were the low output of the first gate The circuit of Fig 1 has little practical use because once the supply has been switched on we cannot change it from whichever of the three states it chooses to select If we attempt to force any input low or high we will find that we are short circuiting a gate output to an opposite polarity from that which it holds with a consequent risk of damage to the gate and certainly the flow of excessive current The situation alters dramatically if we introduce three current limiting resistors in series with the outputs as we do in Fig 2 These resistors have values which limit the gate output current to a safely low value when it is desired to change the state of the circuit Also included in the circuit is a flying lead from the negative VSS supply rail for the gates Let us say that the output of gate C is low and that we want to alter the state of the circuit so that it is gate B output which is low To do this we apply the flying lead to pont Y thereby taking this circuit point low Although the out put of gate B is high the current which flows from it is still at a safe level because of the series current limiting resistor The negative con nection to point Y causes one input of gate C to go low whereupon its output goes high The output of gate A which is already high remains unaltered In consequ
51. having a long plastic spindle and if its body is positioned lower down fitted to a metal bracket This bracket is made up as shown in Fig 3 a from 18 s w g aluminium sheet and it is bolted to the base of the case by two countersunk 4BA bolts with nuts It should be positioned as shown in the photograph of the interior such that there is just room for the PP3 battery between its upright sec tion and the adjacent corner pillar of the case It will be necessary to alter the fength of the upright section of the bracket if the spindle length of the potentiometer differs from that of the component used by the author and this point should be check ed before making up the bracket The meann bracket for TC1 is also made from 18 s w g aluminium sheet and this is shown iniFig 3 b The trimmer is secured to it by two short 6BA bolts and care should be taken to ensure that the adjusting spindle and bush do not touch the inside edge of the central hole The capacitor is mounted with its moving vane tag pointing away from the bend in the bracket The bracket is glued to the inside surface of the front panel with a good quality adhesive such as an epoxy type Those who prefer to do so may alternatively drill two holes in the panel and the bracket to take countersunk RA belts with nuts but this will mean i oe ad heads will be visible from the front of the sei The aerial is bolted in the position shown in the photographs to the bottom
52. he adjacent end cheek It is mounted by first drilling two holes of about 3mm diameter through which its leads covered by sleeving can pass The photocell is then glued in position by means of a good quality adhesive such as an epoxy type Make absolutely certain that its lead outs do not short circuit to the case The printed circuit board is mounted on the in side of the right hand end cheek of the case using two small short woodscrews It is necessary to fit several washers over these screws between the board and the case as otherwise there is a strong risk of the board cracking when the mounting screws are tightened To PCCI Neg in CLOCK MODIFICATIONS After the board has been fitted in position it can be connected to the photoconductive cell lead outs All the insulated leads from the board are shorten ed as necessary when they connect to the cell and to the main printed board of the clock The next process is to modify the clock whereupon it becomes necessary to consult the printed circuit board diagram which was published as Fig 5 in the article describing the clock First identify the copper track which carries the negative supply rail In the view of the copper side of the board this is the track which runs along the bottom and up the right of the board connecting to the emitters of TR1 to TR4 Drill an additional hole through this track at any convenient point and solder the negative input lead from the auto
53. ied punched or un punched The P C Boards for this project are also available For details of this and our standard range of cases send 15p refundable to M ELECTRONICS 275a Fulwood Road Broomhill Sheffield 510 3BD COMPONE RADIO amp TELEVISION For the convenience of en enthusiasts we supply Radio amp Electronics Constructor Data Books Alsoa 55 CS Je world ICS 25 Parnell Street Dublin 1 Telephone 749972 693 Fig 6 Flyback rectification is used to feed the tube first anode and the focus potentiometer FOCUS CIRCUIT Dick peered anxiously at the circuit Could it he asked eventually be after the winding which supplies the focus pot circuit Fig 6 You ve hit it tirst go Dear me you re in very good form today I must admit stated Dick modestly that I have the oc casional flash of genius Right then Down at Joe s Caff for instance they look upon me as being excep tionally brainy Okay so let s Naturally I have to draw a cloak over my brilliance This flyback rectification Otherwise people might look upon me as being big headed Will you flaming well belt up Blimy Smithy what s up with you I want to get on with this dis cussion retorted Smithy heatedly Not listen to you and your mouth Fair enough replied Dick equably Well
54. ing recorded include the mooring forces on the CCR pontoons loadings on the raft hinges hydraulic pressures electrical power output and so on Analysis of the recorded data is finally carried out at one of the NMI s land bases using Honeywell mainframe computers In all four R amp D projects each based on a different mode of wave to mechanical energy transfer are being financed by the 25 million DofE wave energy research programme The other three being under taken by both private industry and Govern ment bodies concern the use of Salter Ducks Oscillating Water Columns and the Russell Rectifier ARS S Picture shows H R H The Duke of Kent dis cussing Multicore Solders Limited Solder Creams with Gordon Arbib the company s Managing Director Also shown are four ex ecutives from Multicore s Hong Kong Distributors Roxy Electric Co Ltd 656 MULTICORE SOLDERS AT THE BRITISH INDUSTRIAL EXHIBITION HONG KONG It was a question of History repeating itself when H R H The Duke of Kent met Gordon Arbib Managing Director of Multicore Solders Limited at the British Industrial Exhibition in Hong Kong His Royal Highness stopped at the Multicore Solders Stand to see demonstrations of their Oxide Free Solder Cream and special solders for the soldering of aluminium Twenty eight years ago Queen Mary visited a Multicore Solders exhibition stand at the Radio Show in London where she met Mr Arbi
55. k How on earth can the symptoms of the screen lighting up at switch off lead you so directly to the brightness control pot Resignedly Smithy rose and walked over to the filing cabinet in which the service sheets were kept After some moments he removed a manual carried it over to Dick and laid it alongside the television receiver He opened out the pages bearing the receiver circuit and in dicated the line output and picture tube section Fig 2 T need the receiver circuit to be able to answer your question he remarked Now if you look at that circuit you ll see there s a winding on the line output transformer which feeds scan pulses via a rec tifier diode to a 1uF electrolytic and the brightness control pot Here hang on a minute what s all this about scan pulses And what s a winding doing on the line output transformer providin these scan pulses anyway I thought that all a line output transformer is sup posed to do is to feed the line scan ning coils and generate e h t for the final anode of the picture tube Even in an ordinary monochrome receiver where the h t is derived direct from the mains Picture tube 95V battery television receiver This is a Slightly orn 1590 1591 Series of television receivers the line output transformer does more than just that It so happens that the set you have here is one of the popular current models which can run eith
56. ker design and manufacture MODEL RADIO CONTROL Third Edition By Paul Newell B Sc 136 pages 210 x 140mm 84 x 5310 Published by Radio Control Publishing Co Ltd Price 2 95 Radio control of models including in particular model aircraft has itsown special fascination The present book has become a standard reference in the U K and appears enlarged and revised in its new third edition The book is available from model shops or may be obtained direct from Radio Modeller magazine High Street Sunningdale Berks SL5 ONF The book starts with a brief historical section then proceeds to its main theme proportional con trol systems These are considered in great detail and included are chapters on digital transmitters digital receivers digital decoders and digital servo amplifiers The text is accompanied by clear diagrams and there is also a wealth of photographs of models and equipment Further to be found are circuits and printed board layouts for an advanced i c digital system This is definitely a book for the radio control buff RADIO AND ELECTRONICS CONSTRUCTOR CMOS DIGIT FREQUENCY N Part 1 2 parts By R A Pent Range 10Hz to 42MHz For the ultimate in accuracy and convenience in use a digital frequency meter easily betters the alternative methods of frequency measurement The unit which is described here is capable of measurements from low audio frequencies up to a typical maximum of about 50MHz 42M
57. le Miscellaneous Verobox type 75 1469 L Stereo headphones 80 per headphone Veroboard 0 lin matrix Trimmer converter see text Control knob 1 5 volt cell type HP7 Ever Ready Ferrite rod 21 x lin see text 32 s w g enamelled copper wire for L1 Insulating tape solder tags wire etc ala Ya T ferrite KAC O Ses Sa agaes tod l 8O turns of 32 swg f enamelled wire Bands of insulation tape Fig 2 Details of the ferrite rod aerial winding FERRITE AERIAL Commercially produced ferrite aerials all seem to be far too large for the present application and so it is necessary for the aerial to be home constructed Details of this component are provid ed in Fig 2 The aerial is wound on a 21 by tin ferrite rod It will probably not be possible to obtain a rod of the required length and so it will be necessary to cut a piece from a longer rod Ferrite is an extremely ard and brittle substance which cannot be easily cut through with say a hacksaw It should be possible to cut a deep groove around the cir cumference of the rod at the point where it is to be cut after which the rod can be easily broken at this point by tapping it gently against the edge of the bench This does not always produce a very neat break but any rough protruding edges can be filed off and any general roughness will not affect per formance The winding consists of 80 turns of 32 s w g enamelled copper
58. le to produce a proper audio output from the set as the oscillating detector will not lock on to the carrier of the received signal and all that will be heard is the beat note produced by the carrier of the jr s nission heterodyning wit Nig ELECTRONICS CONSTRUCTOR hot RAYE 6BA clear eG 4BA clear oF ee After i bending After bending Fig 3 a The mounting bracket for VR1 If this component has a non standard spindle length bracket dimensions may need to be modified as described in the text The mounting bracket for VC1 A Ville aii eaters LL gt gt A 4 on BUUU UUU UUU UUL UMLA 8 m A y gt 4 i APE gg af A A TA gt 4 P 4 y Tg Y cu eM 7 Z ecu Mk amp A h 1 2 P amp e agag 2 gimp ate Maat A Po Mo Two of the r f bypass capacitors are soldered into circuit on the copper side of the board JULY 1978 667 Another view of the receiver The telescopic aerial is slightly more than one metre in length when it is fully extended the oscillating detector VR2 should then be turned back almost 89 far as is possible without oscillation ceasing It is obvious when oscillation has been lost as no signals other than background noise are produced If VR2 is adjusted too close to the point where oscillation ceases the audio output level will be rather low and output q
59. ling between the ZN414 and the transistor whilst C4 rolls off the high frequency response This is necessary as the frequency response of TR1 would otherwise extend well into the r f spectrum which would almost certainly result in instability especially when one considers the very compact component layout which must be used S1 is the on off switch and no supply decoupling components are required The current consump tion of the receiver is about 8mA most of which is JULY 1978 15V Phones 160 TR BC IO9C ZN414 Lead outs BC IO9C Lead outs taken by the output stage Some constructors may be worried by the fact that a standing current from the output stage flows through the headphones This current is not sufficiently high to adversely affect the performance of the headphones even in the long term The transducers used in inexpensive stereo headphones are almost invariable similar to miniature 80 loudspeakers of the type that are found in small radio sets cassette recorders and similar items COMPONENTS Resistors R1 100k watt 5 R2 2 2kQ pre set potentiometer 0 1 watt skeleton horizontal R3 47ka i watt 5 Capacitors 1 0 01uF type C280 Mullard C2 0 1uF type C280 Mullard C3 0 1pF type C280 Mullard C4 3 300pF ceramic plate VC1 20 250pF trimmer see text Inductor L1 ferrite aerial see text Semiconductors 1C1 ZN414 TR1 BC109C Switch S1 s p s t sub miniature togg
60. m TR3 when TR2 is turned off is that flowing through R7 mul tiplied by the current gain of the transistor Despite the relatively high current drawn by the clock cir cuit the voltage drop across TR3 under this condi tion is only about 0 7 volt which is not significant The base of TR1 is fed from a potential divider circuit of which one arm consists of the photocon ductive cell PCC1 and current limiting resistor R1 whilst the other arm consists of the pre set variable resistor R2 Under light conditions PCC1 exhibits a low resistance this increasing to a very high value in excess of several megohms under very dark conditions In consequence light conditions cause the base of TR1 to be taken sufficiently The auto dimmer components assembled on positive for this transistor to be turned on and TR2 their printed board to be cut off whereupon the auto dimmer output is JULY 1978 687 size in Fig 3 Note that R2 is a standard and nota miniature pre set potentiometer It is advisable to mark up the three holes it requires from the tags of the actual component as these may vary slightly from the hole positioning shown in the diagram The two mounting holes are 3 to 3 5mm in diameter Insulated leads about 150mm long are connected to the board at the points where it will eventually connect to PCC1 and the clock circuit The photoconductive cell is mounted on the rear panel of the clock case between the zero reset switch and t
61. nsformer win ding this will be very much smaller than the peak flyback rectification volta e Now what does that bring us to Suddenly his face lit up Tve got it he said excitedly T ve got it If you want a certain rectified voltage with scan rectifica tion you need a lot more turns on the line output transformer winding than you do to get the same voltage with flyback rectification That remarked Smithy ap provingly is it precisely The last thing the TV set maker wants to do is to put an unnecessary number of turns on the line output transformer and so if he wants to obtain a supp ly voltage for a low current circuit he uses flyback rectification It is only when the supply voltage has to feed a high current circuit that he uses scan rectification The polarity of the waveform is governed of course by the end of the winding which is connected to chassis In this particular TV circuit we ve already seen the flyback rectifica tion for the e h t supply Can you see another case of flyback rec tification THE MODERN BOOK CO Largest selection of English amp American radio and technical books in the country 19 21 PRAED STREET LONDON W2 1NP Tel 01 723 4185 2926 5 000 ODDS AND ENDS Mechanical Electrical CAT FREE WHISTON DEPT R E C NEW MILLS STOCKPORT BEC CABINETS BOOK END CHASSIS The DUETTE Stereo Amplifier uses our GB 1 case and can be suppl
62. nually sending cloud cover pictures of the earth from 1 000 miles up These pictures can be received here on earth by anyone equipped with a ground station to receive them and it needn t cost a fortune A sophisticated satellite receiving station can be built for less than 50 The interested reader should first write to the Home Office Radio Regulatory Dept for permis sion to receive satellite signals from satellites operating in the 135 138 Mhz band and a letter granting authority will allow authority to receive signals emitted by artificial earth satellites engaged in scientific space research for the purpose of making observations on the technical NOAA 5 visible light depression off Greenland 684 characteristics of such signals or otherwise carrying on technical in vestigations into radio technique Obviously a receiver to receive this band is re quired The author s route was to feed the output from a converter into a VHF receiver A suitable converter for the satellite band can be purchased or built The 2M converter in the RS handbook can be readily adjusted to cover 136 138 Mhz At the present time 1977 there are two American satellites in orbit NOAA4 and NOAA 5 The prime satellite is NOAA 5 transmitting on 137 5 Mhz with NOAA 4 as back up on 137 62 Mhz The signal from the satellite is transmitted as a wideband FM signal with a 2 4 Mhz AM sub carrier to the ear this sounds like lub dub The satellite pa
63. nversion charts broadcasts in English frequency lists standard frequency and time signal stations solar activity for 1978 co operators and monitors and co operating operating DC clubs together with much other information of assistance to the modern day short wave enthusiast i Also included between the covers of the WRTH is a separate section entitled Listen to the World the contents of which include the following chapters Eight New Short Wave Receivers a review of receivers currently being offered to SWL s Antennas for Broadcasting Reception several practical aerial designs suitable for the stated purposes DXing in Paraguay listening results obtained by Tony Jones a well known Dxer resident in that country Frequency Counters for the Dxer learn all about measuring frequencies Build Your Own Log Periodic Antenna high gain switchable or rotatable aerial systems for the SWLY and Unofficial Radio all about radio pirates and suchlike ie The 32nd Edition of the World Radio TV Hand book is thoroughly recommended to all who operate over the short wave spectrum and it is available direct from The Modern Book Company 19 24 Praed Street London W2 1NP at 8 16 inclusive of postage y 686 WATCH THE WEATHER By T F Weatherley Red sky at night seaweed rain before seven all are traditional ways of telling the weather but today things are different Today there are weather satellites conti
64. nverter shaft fitted with a small control knob However this cannot finally be done until R2 has been adjusted to the correct setting When completed the receiver is glued to the headphone from which the headphone lead emerges It will need to be mounted fairly low down so that it does not obstruct the headband assembly and it is preferable for it to be mounted on a flat surface However if an epoxy adhesive or other type having a good gap filling ability is employed it should be possible to obtain a good bond to a curved surface if necessary ADJUSTMENT R2 should be adjusted so that its slider is at ap proximately the centre of its track before the receiver is initially switched on and tested If results seem to be satisfactory adjusting the slider of R2 slightly in an anticlockwise direction will probably produce a small improvement in sensitiv itv and selectivity Do not adjust R2 too far in the anticlockwise direction though as this will result in the circuit becoming unstable Also it is advisable not to adjust R2 slider to an extreme anticlockwise setting as the low value of resistance it then inserts may cause a relatively high output current to flow in the ZN414 If there is any sign of instability when first testing the receiver such as a whistling sound as the set is tuned across a transmission then R2 slider should be adjusted slightly in a clockwise direction to eliminate this instability Do not adjust it any
65. of the case by means of a 4BA countersunk screw A solder tag is fitted over this screw between the bottom of the aerial and the case and connection to the aerial is made 666 via this tag The aerial passes through a suitable hole in the top of the case and a grommet can be fitted here to produce a neat finish The component panel is secured to the bottom of the case by means of two lin long countersunk 6BA screws Spacing washers or spacing nuts suitably positioned are employed to ensure that the copper side is clear of the centre bottom moun ting pillar The board is oriented such that the holes in row No 1 of Fig 2 are nearer the aerial It is not finally mounted until all connections from it have been made to the other components As can be seen from Fig 2 C2 and C3 are mounted on the tags of VR2 D1 and R2 on the tags of VR1 and C13 on one of the tags of SK1 As already mentioned the battery fits between the bracket for VR1 and the adjacent side moun ting pillar of the case A piece of foam rubber or plastic will hold it in position when the rear of the case is screwed on ADJUSTMENTS Initially TCi should be adjusted for almost maximum capacitance i e its vanes should be nearly fully enmeshed With an earphone or headphones plugged into SK1 the set can then be oeced on and UUO advanced It will probably not vod costet sy means of VR1 un tui viid is well advanced if YR2 is advanced too far it will not be possib
66. off switch and is ganged with VR2 The current consumption of the receiver is ap pon 6mA only whereupon the PP3 attery has a reasonably long life COMPONENTS The telescopic aerial employed with the receiver has a closed length of 176mm and an extended length of 1 1 metres and is hinged for operation at different angles This is available from Maplin Electronic Supplies It has a bracket on the lowest section which is not required here this bracket can be removed by drilling out the two rivets which secure it to the aerial Other telescopic aerials of about the same length with the hinged ae and a 4BA tapped hole in the centre of the base should also be suitable C7 is specified as 0 47uF electrolytic 10V Wkg but in practice it will be found very diffi cult to obtain an electrolytic capacitor of this value at such a low working voltage It will be quite in order to use a capacitor having a much higher working voltage even as high as 100 volts The BF244B specified for TR1 is available from several suppliers including Electro value The 185 by 109 by 60mm plastic case in which the receiver is assembled is retailed by Messrs Brian J Reed Finally the C801 trimmer capacitor specified for TC1 can be obtained from Home Radio COMPONENT PANEL Most of the components are assembled on a 0 lin pitch Veroboard having 32 holes by 14 strips Veroboard is not often used in r f and v h f con structional projects as the ca
67. om line genk driver 1 st I Line it Line output Line output scan Ht transformer 4 700pF transistor coils lt tH Stl Ili To flywheel OI pF Section of on off switch 12V battery Fig 2 Line output stage of a monochrome mains simplified version of the circuit employed in the Th He turned the control in an anti clockwise direction The meter nee dle fell to a near zero reading as the potentiometer slider reached the end of its track He transferred one of the clips to the other end of the track then adjusted the contro so that its slider approached and reached the fully clockwise end of its track This time the meter con tinually indicated a high resistance reading It was obvious that Smithy s diagnosis was completely correct Fig 1 b Hey Smithy You must be hav ing me on Absent mindedly Smithy looked round T beg your pardon I said you must be having me on You must have had a look at this set yourself because the fault was an open circuit to the brightness control track exactly like you said Was it said Smithy pleased Despite my declining years I haven t lost my grip then No I haven t examined the particular set you ve got there but I do know the model fairly well I made a guess at the snag working from that knowledge and it looks as though my guess was pretty inspired JULY 1978 sync stage But I don t get it wailed Dic
68. ore 681 FOR DX LISTENERS By Frank A Baldwin We commence this month by listing some stations on the LF bands for the interest of the Dx i much that follows being on the higher frequen cies CHINA Radio Peking on 4460 at 2210 YL in Chinese in the Domestic Service 1 programme scheduled here from 2000 to 2300 with this transmission Radio Peking on 4800 at 2110 YL in Chinese in the same programme as above Harbin Heilongjiang on 4840 at 2113 YL in Chinese The schedule is from 0825 to 1430 and from 2040 to 0635 Lanchow Gansu on 4865 at 2215 OM and YL alternate in Chinese scheduled here from 0950 to 1600 2120 to 0100 and from 0320 to 0600 Urumchi Xinjiang on 4970 at 1728 signing off with choral rendition of the Internationale In ad dition to local programmes this transmitter relays the Peking Domestic Service in Kazakh the ne is from 2300 to 0030 and from 0130 to 1730 COLOMBIA Emisora Nuevo Mundo Bogota on 4755 at 0417 Latin American music OM with song in Spanish This station has a 24 hour schedule and a pa of kW sometimes identifying as Radio aracol Ondas del Meta Villavicencio on 4885 at 0245 OM with identification in Spanish and into a prograscine cf decal st 15 dance music The scheduis is trom GIU ts 0800 and the power is AKW VENEZUELA Radio Frontera San Antonio on 4760 at 0232 local style pops OM announcer YL with songs in Spanish The sche
69. ous since it provides no voltage gain The load resistor values may also seem rather on the low side However it must be remembered that this amplifier has to function at frequencies up to about 50MHz and so it has to employ high speed transistors TR2 to TR6 have an fT of 500MHz which require com paratively high operating currents Also the input impedance of the subsequent stages tends to fall considerably at high frequencies and so the use of an emitter follower buffer stage helps to maintain the high frequency response TR4 and TR form a fairly conventional Schmitt trigger circuit and this drives the prescaler by way of another emitter follower TR6 R9 is adjusted to produce the best possible sen sitivity At audio and low radio frequencies the set ting of this potentiometer is not particularly critical but in order to obtain good sensitivity at very high frequencies it must be set up quite ac curately C6 is a speed up capacitor which bypasses R11 at high frequencies and provides an improved high frequency response The SN7490AN decade counter actually con tains a divide by five and a divide by two counter It must be connected to first divide by five and then by two as the divide by five counter will operate up to at least 42MHz whereas the divide by two counter will only operate up to about 16MHz or so It must be noted that an ordinary SN7490N decade counter is not suitable for use in this circuit as it will only opera
70. pacitance between strips can cause problems This was not found to be the case here and an early prototype was successfully built on a T Dec Details of the panel are shown in Fig 2 which also illustrates the other wiring Both L1 and L2 are home constructed com ponents L1 consists of about 40 turns of 0 18mm diameter or 36 s w g enamelled copper wire scramble wound on an ordinary 270k watt 10 resistor The resistor has a body diameter of around 0 lin The ends of the winding after scrap ing and tinning are soldered to the resistor lead out wires close to the resistor body so that the win ding cannot spring apart The lead out wires of the resistor then act as the lead out wires of the choke The value of the resistor is not important pro vided that it is 100k or more since it is merely being used as a former L2 is a tuned winding and has to be wound with reasonable precision It employs 0 9mm _ or 20 s w g enamelled copper wire and is self supporting It has exactly 4 turns and is wound on a temporary jin diameter coil former The coil ends are bent down and pass through holes in the Veroboard which are 0 3in apart The turns are RADIO AND ELECTRONICS CONSTRUCTOR ooo O 0 9 TC fixed vanes o o o o gt 000 00 OFT CLA 000000600 0 00 o o O 0 0 0 0 O0 0 O0 o o A B C D E F G H J K L M N o o 0 O 0 O 0 0 O O 0 O 0 O 0 O O O O 0 0 O
71. pack is in two Araldite from a 200 gram sachet being poured to form a small potted assembly The resin and hardener are in separate halves of the sachet being brought together just before use by removing a clip 696 recorde parts one containing the resin and the other the hardener with the two sections kept apart by means of a clip When the clip is removed the two component materials come into contact with each other and can be thoroughly mixed by manipulation The bag is then pierced at one end and the mixture squeezed out to be used as required In the photograph it is being poured into a can con taining electronic components As can be seen there is no requirement for the operator to come into pi vaical contact with the mixture at all The performance of epoxy resins can depart from specification if the two components are not mixed in the correct ratio and the two part sachet is a good way of ensuring that optimum performance is achieved The resin and hardener differ in colour whereupon the operator has a visual means of checking that they are thoroughly mixed before use The mixture consists of CW 1404 GB resin and HY 956 hardener This has a low shrinkage on curing low exothermic temperature rise and a low coefficient of thermal ex pansion As with other epoxy resins the electrical properties are par ticularly good The hardener was chosen to give the mixture rapid curing properties at moderat
72. put of each gate connects first to its current limiting resistor and then to one input of each of the other two gates In Fig 2 the right hand ends of the current limiting resistors were taken negative by means of a direct connection In Fig 3 the correspon ding circuit points are taken negative by way of the touch but tons bridging the two contacts of any touch button with a finger tip provides the negative coupling Although the resistance across the touch button will be of a relatively high value it will still be much lower than the values of R1 R2 and R3 thereby taking the appropriate gate inputs sufficiently low to change the circuit state R4 R5 and R6 are in cluded in the touch button circuits to limit any input currents which may flow because of static voltages to a level which can be reliably handled by the protection diodes inside the i c The gate outputs also connect via R7 R8 and R9 to the bases of the three p n p transistors TR1 TR2 and T R3 When any gate out put goes low the corresponding transistor passes collector current and can supply output loads up to some 30mA or so When touch button 1 is touched ins 9 and 2 of the i c are taken ow The output of the remaining gate at pin 4 also goes low causing TR1 to turn on If touch button 2 is bridged pins 8 and 5 go low as also then does the remaining gate output at pin 3 TR2 is thereby made con ductive and output 2 is turned on B
73. r tising is defined as Direct response advertisements display or y postal bargains where cash has to be sent in advance of goods being delivered Classified and catalogue mail order advertising are excluded RADIO AND ELECTRONICS CONSTRUCTOR ULTRASOUND DISPLAY SYSTEM By Michael Lorant X ray like TV displays employ colour changes to indicate varying densities in human tissue John E Jacobs executive director of the Northwestern University Institute s Biomedical Engineering Centre in the United States has with a team of graduate students developed the first ul trasound imaging system capable of producing X ray like coloured images on a television screen of the inside of a human finger muscle or any other living tissue Clearly discernible blood vessels in the fingers of a hand appear as pulsating blue green or orange lines The array of colours shifts as the hand Working with the first ul _trasound colour imaging system John E Jacobs executive director of Northwestern University Technological Institute s Biomedical Engineering Centre watches the image on the colour TV screen given by the hand of the graduate student on the laft The student s hand is im mersed in a tank of water containing the 3 58MHz ultrasonic receiving transducer In the American N T S C colour TV system 3 58MHz is the chrominance subcarrier frequency changes position in a tank of water containing the transd
74. r the fact that the input signal is divided by ten by the prescaler the unit has the following four ranges 0 to 99 99kHz 0 to 999 9kHz 0 to 9 999MHz and 0 to 99 99MHz Again it must be carefully noted that the upper limit on the last range is likely to be much less than 99 99MHz since as already explained it is deter mined by the capability of the prescaler and the first counter stage i c INPUT CIRCUIT The circuit diagram of the input and prescaler stages is shown in Fig 3 The input buffer amplifier is the Jugfet source follower TR1 This stage provides a high input impedance of about 1M2 as well as a low input capacitance C1 gives d c block ing at the input and Ri Di and D2 provide overload protection With high level inputs the two diodes clip the signal at TR1 gate to about 1 3 volts peak to peak with R1 providing current limiting A very large input signal level would be needed to damage any of the input components C2 bypasses R1 at high frequencies tnereby preventing a top cut filter effect which would be given by R1 and the following input capacitance and which would great ly reduce the sensitivity of the unit at such frequen cies C4 couples the output from TR1 source to the base of the common emitter amplifier TR2 This is direct coupled to the emitter follower TR3 with R4 acting as a bias resistor controlling both stages At first sight an emitter follower at the output of the amplifier may seem_ superflu
75. ridging touch button 3 takes the negative coupling to pins 1 and 6 of the i c with the result that pin 10 goes low and TR3 conducts It is a little difficult to devise a simple means of biasing the circuit such that a particular output is always the first one to be turned on when power is applied which may be a desirable feature in some applications In practice however it would seem that this facility is automatically provided by the nature of the circuit itself since there must be a difference in the current gains of the three gates With the prototype circuit it was found that the same output always came on first whenever the supply was applied Such a perfor mance cannot be guaranteed with all CD4011 i c s of course and the Vop 9V Vss particular output which comes on first will vary between one i c and the next The outputs to be controlled de pend upon the requirements of the constructor If a relay is to be used in an output circuit it will require the usual reverse connected diode across its coil as is illustrated in Fig 4 The three touch buttons will need to be home constructed each con sisting of two small pieces of metal having a shiny surface which gives good contacts to the skin of the finger The heads of two nickel plated bolts of around 4BA or 2BA mounted close to each other on a piece of insulating material can provide a simple and rine made touch button The touch but
76. sent state of development the method appears to be particularly ap propriate for absorbing sound in air ducts and fluid pipelines It is commonly accepted that a loudspeaker can be used to cancel sound waves in one direction at the expense of doubling the sound levels in another but the fact that a loudspeaker can be employed to ab sorb sound energy thus forming a sound sucker 1s less well known Assuming that the noise from a fan for instance is travelling along a duct and that it is required to silence this noise before it reaches the area serviced by the duct the following method is adopted Two microphones are placed in the duct and their outputs are com bined to detect only the sound arriving from the noise source The microphone signal is electronically rocessed and is then fed to two oudspeakers mounted on the wall of the duct These operate to produce a 21606 wave which travels down the duct towards the zone to be silenced but not towards the original noise source The plane wave has identical amplitude but opposite phase to the unwanted sound and the end result is silence in the duct downstream from the loudspeakers with an unaltered sound field upstream Under such circumstances it can be shown that the sound energy is first trapped between the loudspeakers and is then progressively absorbed by the loudspeaker nearer the micro phones The experimental system has significantly cut random
77. settings of the con trol Returning it to a central posi tion Dick frowned as he mentally totted up the faults which could cause the loss of raster and picture a faulty tube a faulty tube heater supply a failure in the e h t voltage supply to the tube final anode in correct operation of the line output line oscillator or line driver stages or an unserviceable supply to any of the remaining tube electrodes Blimey he muttered glumly this one s going to be a stinker He switched off the receiver At once the screen of the tube lit up to fade away into its previous darkness after a few short moments BRIGHTNESS CONTROL Incredulously Dick gaped at the receiver With a trembling hand he turned it on again with the result that the sound signal became audi ble once more The face of the pic ture tube repeated its performance and remained completely blank Dick waited for a minute then turn 690 Scan and Flyback Rectification The Line Output Power ed the set off The screen became il luminated for a brief period before it returned to its previous darkness Hey Smithy The Serviceman preoccupied with a dismembered music centre on his own bench gave no indica tion that he had heard his assistant Hey Smithy Irritably Smithy put down his test prods For goodness sake what is it now I ve got a set here that s haunted It only comes on when I switch it
78. slow it down a bit by using a large value electrolytic for the capacitance Several hundred microfarads in conjunction with resistances in the order of 100k Q can give an overall cycle lasting some 10 or 20 seconds Just connect a voltmeter across the output of a 555 slowed down in this manner and vou can see its waveshape It pavs every now and again just to remember that all the alternating voltages and currents we deal with are all accurately determined in what is perhaps the most ephemeral dimension of them all time itself RADIO AND ELECTRONICS CONSTRUCTOR
79. switch enabling gate Electronic counter Precision pulse generator RADIO AND ELECTRONICS CONSTRUCTOR AL IETER old Crystal controlled gating pulse Printed circuit modular construction imum of 99 99kHz as there would be only one tenth earlier this last range is operable in practice up toa of the previous time for the maximum count to be typical figure of 50MHz reached and therefore ten times the input frequen cy would be peed to saa ae Shortening the gate time to 10 milliseconds would produce a range of up to 999 9kHz further shortening it to 1 ACTUAL ARRANGEMENT millisecond would increase the range to 9 999MHz A practical digital frequency meter tends to be and so on very much more complicated than the diagram of In the present unit the frequency ranges have Fig 1 would suggest This will become immediately maximum figures of 99 99kHz 999 9kHz apparent with reference to the block diagram of the 9 999MHz and 99 99MHz As was mentioned unit which is shown in Fig 2 Input Input 7 segment 7 segment 7segment 7segment circuitry j display display display display Clock 10 10 10 Paa soas baa an pli hls Clock Display Display Display Display enabie enable enable enable enable JN 99 99kHz Reset q hye 9 R t ange 2 999 9kHz switch Divide by 10 9 999MHz 4 2 Clock 99 99MHz enable 4017 4017 4017 4017 4017 tOkHz tkHz OOHz IOHz IHz 4017 BCIO7 80107 lOOkHz Buffer IMH
80. t current limiting resistors With the 12 volt supply which is used here an out put current of about 10mA per segment is obtained This is more than adequate for high brightness dis 680 plays such as the DL704 devices which are specified The letters A to G around each 4026 apply to the appropriate display segments Each 4026 i c has a display enable output but only that of IC12 is used here This output drives the applicable decimal point via S1 b which is of course part of the range switch Incidentally the DL704 displays have a right hand decimal point S2 is the reset switch and when this push button is operated the reset terminals of IC9 to IC13 are connected to the positive supply rail This resets them all to zero and they are held in this state until the switch is released The unit then makes a measurement of the input frequency in the manner described earler R26 R27 and R28 are included to ensure that at no time is an input of any i c left floating This could otherwise occur with the modular form of construction which is employed here if it happened that external connections to the printed Beard were not completed A floating i c input is highly unde sirable as CMOS i c s can be damaged if high static voltages appear at an input One advantage of CMOS i c s is that they have a high degree of immunity to noise and therefore re quire very little in the way of supply decoupling In this cas
81. t virtually aa tion to point Y The sequence of operations is that the negative con i i Current limiting resistors Fig 2 Adding output current limiting resistors enables the circuit to be changed from one state to another Vpop 9V e T Fle le TR 7602 us TR3 ay BC 2 4 BC2I4L BC2I4L Outputs 2 3 aa 1000 Touch buttons bce BC 214L Re 3 Lead outs lOOkn D 89 4watt 10 uss Fig 3 4 practical circuit in which three outputs can be provided by momentarily touching one of the three touch buttons JULY 1978 659 zero current flows into a CMOS gate input means that the resistors can have any value above that which limits gate output currents to a safe value TOUCH BUTTON OPERATION One obvious application for a 3 way CMOS latch is as a touch button switch in which one of three out puts can be selected by applying a finger to the appropriate touch but ton A working 3 way touch button circuit is illustrated in Fig 3 where it will be seen that the CMOS i c employed is a quad 2 input NAND gate type CD4011 Only three of the ag in the i c are used The fourth as its inputs at pins 12 and 13 taken to the negative rail and no connecton is made to its output at pin 11 The three remaining gates are connected in the circuit of Fig 2 the three current limiting resistors being R1 R2 and R3 If the circuit is traced through it will be seen that the out
82. te overhead at about 10 30 am local time each day NOAA 5 Same depression over UK RADIO AND ELECTRONICS CONSTRUCTOR FM poor s Converter Stereo recorder receiver Time base CRT drivers display be E pa a haa aai ai a m a Aa Block diagram of Satellite 7 Receiving set up The block diagram Fig 1 shows the sections of the display unit On receive the unit generates a 2 4 Mhz reference tone which is recorded on one track of a stereo recording while the satellite signal is recorded on the other In the display mode the received signal and the reference tone are replayed into the display unit The received signal is cleaned up with an active filter and is used to brighten the trace on a Cathode Ray tube The reference signal is phase locked and used to generate the horizontal time base 4 5 Hz The vertical time base is seven minutes and is reset with a switch With such a slow picture build up a conventional CRT will not display a picture but an ex radar tube with an orange phosphor gives a reasonable picture in a darkened room The picture is best recorded JULY 1978 The Display unit NOAA 5 Composite of two photos cloud cover over Western Europe and UK at night photographed in Infra Red Light photographically and the photographs show some of the results to date The interested experimenter will find the Weather Satellite Handbook published by 73 Magazine gives much use
83. te satisfactorily up to about 16MHz The SN7490AN can be obtained from Maplin Electronic Supplies who can also supply the tran sistors type ZTX313 and the voltage regulators specified for 101 and 1014 The remaining semiconductor devices apart from the l e d dis plays are available from Maplin Electronic Supplies and from other suppliers TR7 is a common emitter ae which provides interfacing between the t t l and CMOS ITY 1978 TR N x N wo N circuits This transistor is powered from the main 12 volt supply line so that it provides virtually 12 volts peak to peak for the following CMOS counter R15 limits TR7 base current to a safe value and C10 is a speed up capacitor The prescaler and input stages are powered from a 5 volt line which is derived from the main 12 volt supply by means of the monolithic voltage RADIO AND ELECTRONICS CONSTRUCTOR 2N2369A BCIO9 Lead outs 2TX3I3 Lead outs 2N5245 Lead outs regulator IC1 R17 lowers the voltage at the input of the regulator and thus reduces its dissipation C3 C7 C8 and C9 are the usual supply decoupling capacitors It should be mentioned that some data tables show the source and drain lead outs for the 2N5245 transposed from the layout given in the lead out inset The 2N5245 functions satisfactorily with the lead out connections given in Fig 3 677 Fig 4 Component and copper sides of the printed board
84. that they are built onto the headphones A case which measures only 71 5 by 49 by 24 5 mm houses a completely self contained fully tuneable medium wave receiver including a ferrite aerial and battery As can be seen from the accompanying photographs the set is mounted on one earpiece of a pair of inexpensive 82 stereo headphones 652 A M RECEIVER Obviously the output of the set will not be of true Hi Fi quality as the receiver is an a m model Also the output is only monophonic with the two headphones being wired in series Nevertheless results are good with regard to quality and the set compares very favourably with most other portable receivers in this respect regardless of whether they are of the loudspeaker or earphone output variety It would of course be possible to feed most monophonic receivers into a pair of inexpensive stereo headphones and obtain very similar results but there would then be the disadvantage of a trail RADIO AND ELECTRONICS CONSTRUCTOR Fig 1 The circuit of the headphone receiver The headphones are two amp Q un its in series and give ade quate volume after the a f amplification provided by TRI ing lead between the headphones and the receiver Ordinary simple earphone receivers with which this set is roughly comparable in complexity also suffer from the same disadvantage One might expect this radio to be rather difficult to build due to the small size into which the elec
85. tion and a relatively high voltage of the order of 95 volts appears across the 1uF reservoir capacitor following the rectifier This voltage feeds the collector load of the video output transistor It also feeds the brightness control pot which is the one you found to be faulty It will be almost certain that the track was open circuit at the high brightness end where it connects to chassis That s right agreed Dick It was the end where the knob was turned fully clockwise Which reminds me all over again how on earth did you know that the fault was there Because this particular set has a rather unusual on off switching cir cuit which we haven t talked about yet replied Smithy The on off switch has three poles two of which switch the mains supply whilst the third switches battery negative to chassis when the set operates from a 12 volt battery When this third pole goes to the off position it connects the slider of the brightness control pot to chassis whereupon the tube passes a fairly heavy current between cathode and final anode and largely discharges the e h t reservoir capacitance The result is that you don t get that little spot appearing on the centre of the screen after you switch off whilst the tube cathode is still hot Also you don t have a lot of e h t volts hanging around Of course of course I see it now said Dick When the set was on the open circ
86. tion and the news in English PHILIPPINES FEBC Far East Broadcasting Company Manila on 11765 at 0918 OM with a religious programme to Australia New Zealand and New uinea Radio Veritas Manila on 11955 at 1415 YL with a talk on travel in the Far East in the English progr rme scheduled from 1400 to 1500 on this channel eels CHINA Radio Peking on 9945 at 1135 YL in Viet namese Chinese music in a programme for Viet nam scheduled here from 1130 to 1200 also from 1330 to 1430 Radio Peking on 9920 at 1430 OM and YL in the Kazakh programme Domestic Minority Groups schedule from 1400 to 1455 Radio Peking on 9880 at 1425 Chinese orchestral music in a programme intended for In donesia scheduled from 1400 to 1430 Radio Peking on 9390 at 1440 YL in Tagalog to the Philippines scheduled from 1430 to 1500 Radio Peking on 11650 at 1428 OM in the English programme for South East Asia scheduled irom 1400 to 1500 Radio Peking on 11695 at 1433 OM with a programme for Cambodia scheduled from 1400 to 1500 on this channel JULY 1978 BRAZIL Radio Relogio Rio de Janeiro on 4905 at 025847 OM in Portuguese with announcements time pipsy off at 0302 without National Anthem A Voz do Oeste Cuiaba on 4775 at 0015 OM with identification in Portuguese local style musica Schedule is from 1000 to 0300 and the power is 1 5kW Radio Pioneira Teresina on a measured 5016 at 0242 announc
87. tons themselves should be spaced apart such that there is little risk of two buttons being inadvertently touch ed at the same time This will not cause any damage to the i c but may prevent correct output selec tion If the equipment in which the touch button circuit is employed has a chassis which is at earth potential this may be made com mon with the touch button negative supply On no account must the circuit be so used with equipment having a live chassis connected to the mains supply as occurs with many televi sion receivers a a aaa aaacasa Mail Order Protection Scheme The publishers of this magazine have given to the Director General of Fair Trading an undertaking to refund money sent by readers in response to mail order advertisements placed in this magazine by mail order traders who fail to supply goods or refund money and who have become the subject of liquida tion or bankruptcy proceedings These refunds are made voluntarily and are subject to proof that pay ment was made to the advertiser for goods ordered through an advertisement in this magazine The arrangement does not apply to any failure to supply goods advertised in a catalogue or direct mail solicita tion 660 If a mail order trader fails readers are advised to lodge a claim with the Advertisement Manager of this magazine within 3 months of the appearance of the advertisement _ For the purpose of this scheme mail order adve
88. tronics must be condensed However this is not really the case and construction of the project is quite simple and straightforward All the com ponents are standard readily available items and power is obtained from a single HP7 1 5 volt cell The set is therefore very economical to run es pecially when one considers that the cell will have a long life even if the receiver is used extensively THE CIRCUIT As can be seen from Fig 1 the circuit of the receiver is extremely simple and is based on the popular ZN414 integrated circuit This device con tains most of the components for a sensitive medium wave t r f receiver including the r f amplifier detector and a g c circuitry A ferrite aerial and tuning capacitor are re quired and these are L1 and VC1 respectively C1 provides an earth return path for one side of the tuned circuit and R1 is the bias resistor for the ZN414 R2 is its load resistor and it is across this component that the audio output signal is developed C2 is an r f filter capacitor The ZN414 provides an audio output level of about 30 millivolts r m s from a source impedance of a few hundred ohms This is not really sufficient to adequately drive 82 headphones and some ad ditional audio amplification must be employed The amplification is provided by TR1 which is wired as a high gain common emitter amplifier TRI1 is biased by R3 and the headphones form the collector load C3 provides interstage coup
89. uality will be a little poor Careful adjustment of VR2 is needed for op timum results Virtually all f m broadcast transmitters use horizontal polarization and so the telescopic aerial should be slanted at 45 degrees rather than left ina vertical position It should be rotated to the posi tion which gives the strongest signal bearing in mind that the seting of VR2 becomes less critical as signal strength increases A strong signal also gives broader and easier tuning Tuning ranpe at the low frequency end of the band is controlled by TC1 Adjusting TC1 for in creased capacitance extends the range in the low frequency direction If the range does not extend low enough with TC1 at maximum capacitance coil L2 can be compressed slightly to increase its inductance Conversely when there is insufficient in the high frequency direction L2 can be stretch ed out slightly in order to reduce its inductance In this situation do not adjust TC1 for decreased capacitance as this would reduce the overall tun ing range hen one considers the simplicity of the circuit the audio quality output of the prototype is very good if used with low impedance 16 n headphones or high impedance 4 000 0 headphones Although still acceptable results are not as good with a crystal earpiece This gives a noticeably reduced bass and lower middle frequency response which j subjectively results in a lower signal to noise ratio DECIMAL
90. ucer device The colours do not represent real colours in the internal structure of the hand Instead they repre sent varying rates at which ultrasound waves pass through the hand when it is dipped in a tank of water in the path of the waves A normal unimpeded sound shows up on the TV screen as red Sound waves arriving slightly later and thereby at different phases appear successive ly as purple blue green and orange All hues JULY 1978 recognisable by the human eye on a standard colour scale appear as the sound wave phase patterns alter Ultrasound wave interference patterns are set up by the varying arrival times of the waves on a two inch round quartz plate operating at 3 58MHz The plate is part of an imaging tube at one end of the tank which translates the ultrasound waves emanating from the other end into the different colours seen on the TV tube There are three important advantages of the eps which will allow it to be used as a medical iagnostic tool First it can produce bright simultaneous images of pulsating blood vessels in muscle and other tissues not normally visible by conventional X rays Second the colour television system is 20 to 40 times more sensitive to tissue changes than existing black and white displays of ultrasound images Finally by using scattering and reflecting techniques similar to those employed in SONAR the system could be used to diagnose diseased conditions in human tissue
91. uit to the pot track meant that the tube cathode was always highly positive with respect 10010 Brightness Section of on off switch Off On Fig 7 The higher current 95 volt supply for the video output stage is provided by scan rectification The cross indicates the position of the open circuit in the faulty brightness control potentiometer RADIO AND ELECTRONICS CONSTRUCTOR O lpF To flywheel E sync stage i Clamped at chassis potential Fig 8 Yet some further outputs from the line output transformer The tap in the lower winding provides line blanking pulses for the picture tube grid together with negative going flyback pulses to the flywheel sync stage to the tube grid regardless of the position of the pot slider Switching off shorted the pot slider to chassis and took the tube cathode suf ficiently negative for the tube to pass current and light up the screen It s obvious now when you look at it POWER HOUSE Exactly chimed in Smithy Taking the tube cathode highly positive of the grid caused the tube to cut off because this is the same as taking the grid highly negative of the cathode As you can see from the main circuit the grid is held at chassis potential by way of the 10kQ and 33kQ resistors which couple it to the chassis So there you are Dick You ve got a TV set in front of you which has a positive supply rail of only 11 5 volts feeding the line output
92. urvival capability of the Cockerell Contouring Rafts CCR Based on an analysis of the data obtained a full size prototype will be designed for further evaluation For the th scale experiments the SE7000 is housed together with all the other measuring and real time data analysis equipment in a 20 ton ISO container secured in the hold of a moored 60ft sea going barge This barge is linked to the CCR by means of an electrical umbilical cable The tape transport is being used to record pulse code modulated 0010 signals derived from 64 data channels With such a large number of channels conventional analogue tape recording would have been prohibitively expensive pcm techniques developed by Microconsultants Ltd in association COTTERELL CONTOURING RAFT TAoth SCALE EXPERIMENTAL PROTOTYPE The Cockerell Contouring Rafts are hydraulic electrical systems whereby the wave induced movements of the articulated sections are converted into a hydraulic pressure which is then itself converted into electrical energy using an alternator with the NMI were therefore used since these enable up to 21 data channels to be recorded on only one track of the 14 track recorder The measurements being monitored relate to en vironmental conditions such as wind and current speeds and directions tide and wave heights and directions using a device developed by the British Ship Research Association barometric pressure etc Other parameters be
93. ves detailed information on the building of test equipment and the manner in which it may be used The present second edition has a completely revised text and has many new designs including digital instruments and microwave test gear The test equipment covered includes everything that can conceivably be required for normal amateur work and takes in the measurement of voltage current frequency r f power noise aerial standing waves and many other quantities The book also has the attractive well drawn diagrams which are associated with R S G B publications The price at the head of this review is that applicable in the U K and the volume may be obtained direct from Radio Society of Great Britain 35 Doughty Street London WC1N 2AE at this price plus at the time of writing 67p postage and packing JULY 1978 Cheerfully Dick plugged an aerial lead into the 14 inch black and white television receiver after which he inserted its plug into one of the mains sockets ranged along the rear of his bench He switched the set on whereupon the sound signal from one of the local u h f channels became audible from its speaker Expectantly he waited for the cathode ray tube to warm up and the consequent appearance of a picture Nothing happened There was no picture not even a blank un modulated raster He leaned forward located the brightness control and adjusted it experimentally The screen remain ed blank at all
94. wscast in the English programme to Europe and North America scheduled from 2130 to 2255 and in parallel on 7170 Turkiye Polis Radyosu Turkish Police Radio Ankara on 6340 at 1519 local type music YL RADIO AND ELECTRONICS CONSTRUCTOR with songs OM in Turkish Scheduled from 0600 to 1100 1200 to 1600 and from 1730 to 1900 GREECE Athens on 17830 at 1532 typical local type ee M and YL alternate with announcements in Greek PAKISTAN Karachi on 6235 at 1943 OM with a talk in Urdu in the World Service to the U K and Europe scheduled here and in parallel on 4718 and 7095 from 1915 to 2115 in Urdu and from 2115 to 2145 in Sylheti W GERMANY Cologne on 6100 at 0130 OM with a newscast in the English programme intended for the East Coast of North America scheduled from 0130 to 0200 and transmitted from the relay station at Cyclops Malta on this channel AUSTRALIA Melbourne on 11900 at 1519 YL with the prokramine Australian Editorial Opinion in the nglish transmission to Asia and the Pacific Time check 5 pips and a newscast in English after sta tion identification at 1600 Melbourne on 11705 at 0946 YL with listeners record requests in the English programme to the Pacific Islands Melbourne on 9670 at 1450 OM with the English programme to Papua New Guinea iden tification and world news at 1500 NEW ZEALAND Wellington on 11820 at 0900 OM with time 160 station identifica
95. z xtal osc Fig 2 In practice the frequency meter is more complicated than is evident from Fig 1 However the use of integrated circuits simplifies construction to a considerable extent JULY 1978 673 4017 It is only necessary to connect the inverted control pulse to the clock enable input of the first counter since if the input signal is blocked at the first counter it obviously cannot reach any subse quent counter The three other 4026 i c s therefore have their clock enable inputs permanently con nected to the negative supply rail The 4017 i c also has a clock enable input and its 2 output is connected to this input During circuit operation as so far described the 2 output is low allowing the 4017 to operate normally but after the 1 output has gone high for one output cycle the 2 output goes high It thereby takes the 4017 clock enable input high as well and the cir cuit latches in this state with the 2 output high and the input clock signal received from ihe divider chain blocked The length of the output pulse of the 4017 i c depends upon the position of the range switch If this switch connects a 1Hz clock signal to the device then obviously an output pulse of one se cond i e the length of one input cycle will be produced 10Hz 100Hz and 1kHz input frequen cies produce output pulses of 100 milliseconds 10 milliseconds and 1 millisecond respectively Therefore allowing fo

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