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AIRMEC RadiVet Model 211

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1. 1 CORRECT BIAS POtNT rn F BIAS AMPLITUDE FIG 6 RADIVET TYPE 211 FIGURE 7 LISSAJOU PATTERN 58 WVYOVIG LINDYIO tte AdAL LAAIGVY EL 3MDOIS 234404 HOLVINILLV A 9494 ISC QI Y IG H OT QI 4210 i 00 6 6 0095 248 sfxg 6 OH XT L SPALL 3H ANI 9995 shai 9 V 95 vL 9 5 gt 51 012 2 6 00V S sa S 2915 CLIVE sh 05 vw GQ TAL les HUM DIHI YYA f s 01 S cc LS 01 29 5 06 ys Vaz DIY BA lt BON 3384 gt IS 127 OF XIV I sf 09 2 sm 61 0 USHA AVA sos thes 5 205 7 SPW 85 011 00X IW 5 gt 07 1 w lt 1 0 5 205 330 4 340 71 83 M MIND a aed O M V 380 d Sty a 823 TT LINONID LLZ 3dAL LSAIOWY At anod 00 BL 7 SLB SSNLHDIE Y 36 37 818 380d 0 8 50 00090 55000004 ANNI 2 3goud
2. X PLATES 50 c s or any ofthe 4 TB ranges TUNING Reguired alignment freguency RF FREQ RANGE 85 mc s normal or 20 db as reqd OUTPUT Sufficiently high to just operate limiter stage With the RadiVet connected as above advance the RF OUTPUT control until the amplitude of the crt trace stops increasing with increased input Continue to turn the control for approximately 1 8 past this point to ensure that the signal input is operating the limiter without overloading the receiver Adjust the GAIN switch and receiver volume control to obtain a crt display of about 1 in height and note any changes in display amplitude as the AUDIO OSC control is switched over the frequency range of the audio amplifier A level output indicates correct de emphasis whilst a lack of de emphasis results in an output which increases with frequency If the output decreases with increased frequency the cause may be too much de emphasis but in any case the checks enumerated in Sections 6 1 and 6 2 pages 19 amp 20 should be carried out to prove that the AF amplifier response is normal This provision is made because the setting of tone controls or a faulty amplifier can materially alter the overall characteristics 4 TESTS ON AM RECEIVERS The output frequency specification limits of 40 kc s assume great importance at the low frequencies required for the correct alignment of IF stages and the Long and Medium wavebands of AM broadcast recei
3. 200ke s Figure 3 Bandwidth measurement of LF response curve AIRMEC RADIVET MODEL 211 PAGE 4 OF 37 AUDIO OSCILLATOR The Audio Frequency Oscillator incorporated provides eleven fixed frequencies covering the range 40 c s to US ke s Resiteance Capacity type of oscillator circuit wich thermistor control is employed to ensure high stabil ity and purity of waveform The output signal which is continuously variable from about 5 millivolts to 2 volts peak to peak is available for external use an LF Outpur lead adjust ment of the switches on the front panel it can at the same time be internally applied to either the X or Y plates of the Oscilloscope snd also used to both Ampli tude sad Frequency Modulate the Signal The Output level is stabilised so that it normally re maint constant over the complete audio frequency range and its amplitude can be metered by twitching it to the e Y plates of the Oscitloscope and measuring it with the Catibrated Y Shift Figure 4 a Wobbulator display of discriminator characteristic Frequency Modulation receiver COMBINED MODULATION A very important feature of the instrument is the ability to modulate the output signal both in amplitude and frequency at the same time This provides the only satisfactory method of checking and adjustirg the fimising action of discriminators and ratio etectors The signal is normalty frequency modulated a
4. Audio oscillator and oscilloscope Audio oscillator and oscilloscope Audio oscillator Audio oscillator oscilloscope and calibrated Y shift Oscilloscope and calibrated Y shift Oscilloscope and calibrated Y shift Oscilloscope with time base adjusted as required AIRMEC RADIVET MODEL 211 PAGE 7 OF 37 SPECIFICATION Cont Time Base Hard Valve Scanning speeds gt 50 milliseconds to 100 in 4 continuensly ranges Additionally the time base deflection may be sinusoids st SO cjs or wt any ol the frequencies availabie from the Audio Orcilistor Y AMPLIFIER The input impedance under conditions is 1 Megohm and under D C conditions i 10 Megohms Attenuation it provided having division cation of t 3 0 100 os AC connections and 16 30 160 300 and on DC connections The gain of the Y Amplifier is approximately es Frequency Response OC the gein at 700 being not more thin db down on that at koju The Y hifi control is calibrated from 10V to LOV in of 02 and in RMS values OLAV in steps ol IV RHS Voltage Measurement The accuracy of mairurement ix 10 ranges which art me 0 cj AX with no AL superimposed D C DC 8 140 RMS AHS 01000 Bed RMS 9 RMI 9 49 97207 AMS 0 70 AMS RX 8 20 RMS AMS Dd 8 47 AHS 077 AMS 4 iv PROBES The following probes are permanently connected to the instrume
5. direct reading accuracy to be obtained without recourse to interpolation The main scale is calibrated in Mc s steps only the number of ke s being read on subsidiary scale which is calibrated 10 ke s intervals For example 14 425 Mc s appears as 14 on the main scale and 0 425 on the subsidiary scale as shown in Figure 1 Since one complete revoluticn of the yebsid lacy scale only changes the frequency by Mc s an effect ive scale length of almest 10 inches per megacycie is obtained over the whole tuning range oven at the end of the highest frequency range This expanded fre quency scale not only provides a very high secting accur acy but enables bandwidths of IF response curve and discriminator characteristics to be measured directly in frequency whcn the RadiVet is used as a wobbulator SCALE NDICATION GETWEEK ALS 949 OR Kh gt 9 4 5 7 4 CATION 2042 TUNING 40 429 CONTROL IF RANGE SELECTOR 15 AT 5 Kh FREQUINCY SETTING 15 J 14 425 sh Figure 1 Tuning Dial te will be appreciated that full advantage can only bs taken of this long tuning scale if firstly the tuning drive is entirely free from backlash and if secondly some means is provided for correcting the scale crystal standard The first requirement is dealt with by employ ing a smooth anci backlash geared couptiny beswc
6. incorporated to ensure a display The Time Base employs hard valve circuit which pro vides scanning speeds continuously varisble ram about 50 milliseconds to 100 microseconds in four ranges Syn ehranisation is extremely good and completely auto matic no externi synchronisation connections being Figure 6 demonstrates just how positive this nchronisation is and it displays the output from the Audio Oscillator at 5 ke s Figure 6 Output from Audio Oscillator et 5 kejs viewed on the oscilloscope AIRMEC RADIVET MODEL 211 PAGE 6 OF 37 In addition the X plates be connected via the X amplifier either to an internal 50 c s signal for use on wobbulator displays or to the output from the Audio Oxclilater This tatter facility enables harmonic and phase distortion to be detected either in the audio frequency amplifier or throughout the complete receiver This is effected by feeding either a modulated R F Signal into the R F LF stages or an Signal to the audio fre quency stages and applying the audio output to the Y plates of the Oscilloscope If the same signal is then applied to the X plates time base a straight diagonal Mae should appear on the CRT shown in Figure 5a Harmonic distortion generated in the receiver causes the trace to curve Figure 5b and phase distortion causes the atraight line to open out into a loop Figure 5 Thus for the first time the Ser
7. of AM receivers will generally have a range of about 400 c s to 5 kc s whilst some FM receivers might have a very much wider range When making overall response checks on any receiver the limitations of the audio amplifier must always be borne in mind if a true picture of the performance is to be obtained Hi Fi eguipment and public address systems will probably reproduce the full range of freguencies from 400 c s to 15 kc s with little or no distortion AIRMEC RADIVET MODEL 211 20 37 Information the characteristics of type of tone control obtained by performing these tests with the tone control in its extreme positions and plotting the curves so obtained 5 1 Distortion check and phase shift measurement Probe or Switch Connection or Setting Probe A RF Not used Probe B Audio Input to first AF stage Probe Oscilloscope Loudspeaker terminals OUTPUT Any position except XTAL CHECK AUDIO OSC Frequency required See text AUDIO OUTPUT As required GAIN AC position as required to give a crt display of reasonable amplitude without overloading the Y amp X PLATES VAR OSC Connect the RadiVet as tabled above and switch the AUDIO OSC to 40 c s If the output is pure inclined linear trace as shown in Fig 3d will be obtained A rapid check to see that the RadiVet is not causing distortion can be made by switching the Y GAIN to INT CHECK A straight line
8. pf C32 0 005 mf C64 560 pf AIRMEC RADIVET MODEL 211 32 37 TABLE 1 contd SCHEDULE OF COMPONENTS Reference Description Reference Description C65 560 pf C73 10 pf C66 560 pf C74 10 pf C67 560 pf C75 SPECIAL 68 0 02 mf C76 260 pf Var C69 0 02 mf C77 200 pf C70 1500 pf C78 22 pf C71 1500 pf C79 530 pf C72 47 pf C80 V1 12 AT 7 V5 PCF 80 V2 PCF 80 V6 DG 76 V3 PCF 80 V7 6X5GT V4 PCF 80 F1 2 Amperes LP1 6 3v 0 3a X1 Crystal 5 mc s 33 37 AIRMEC RADIVET MODEL 211 RI YS My guns 2 Rapier 21 View LOCATIDH MAJOR COMPONENTS AIRMEC RADIVET MODEL 211 PAGE 34 OF 37 FIG 3 RADIVET TYPE 211 WAVEFORMS AIRMEC RADIVET MODEL 211 PAGE 35 OF 37 IF WAVEFORM WITH bdb POSITION N URSOR CE ND ATION S HERDING FOS UNDER OURS 15 BETWEEN 4 5 TYPICAL FREQUENCY OR 9 AND 10 10 6 Mc fs OR I4AND 15 ACCORDING TO RANGE IF WAVEFORM OF A MOVED TO PLACE b db POSITION OF TRALING EDGE UNDER CURSOR SUBSIDIARY SCALE INDICATION SHOWN AT 0 425 TYPICAL FREQUENCY is 10 8 Mc s RANGE SELECTOR IS AT 10 15M cs EREGUENCY SETTING SHOWN 15 140225 Meja 1 ONO BETWEEN 696 LIMITS AU O bMck IO 8Mc s 200k FIGURE 4 RADIVET TYPE 21 BANDWIDTH MEASUREMENT TUNING DEAL FIGURE S RADIVET 211 NORMALLY 2 db OUTPUT LEVEL
9. probe C for all AC and DC inputs to the oscilloscope Audio Lead probe B for all Audio Frequency outputs Earthing As the chassis is isolated from the mains earth universal receivers may be checked without difficulty Power Supplies The instrument operates from supplies of 100 150 and 200 250v at 40 60 c s with a consumption of approx 45 watts The mains lead is permanently connected to the instrument and can be stowed with the probes when the instrument is being transported Dimensions The overall dimensions are 15 32 long x 9 2 deep x 8 high 39 4 x 24 1 x 21 6 cms Weight The total weight of the instrument is approximately 27 Ibs 12 27 kgs Finish The robust steel case is stoved in oyster grey enamel with a glass hard hammer finish effect The front panel is either polished black with white coding or sprayed grey with black coding 10 MAINTENANCE Valve types have been chosen so that replacements if required are available in most service departments Any valves other than V5 or V1 may be replaced without the necessity for adjustment If it should be found necessary to change valve V1 or V5 the following action is reguired a If V is replaced the RadiVet should be connected to a receiver as for IF ALIGNMENT as detailed in Sect 4 1 The core of L7 should be adjusted for maximum response and then sealed with wax b If V1 is replaced the frequency should be checked against the crystal at the HF e
10. time base provides scanning speeds of 50 milli seconds to 100 micro seconds in 4 variable ranges Additionally the time base X deflection may be sinusoidal at 50 c s or at any of the frequencies available from the Audio Oscillator Y Amplifier The gain of the Y Amplifier is approximately 50 times and the deflection sensitivity approximately 0 7 volts cm An input attenuator provides division ratios of 1 3 10 30 and 100 on AC and 10 30 100 300 and 1000 on DC connections The frequency response of the Y Amplifier is from DC to 1 mc s the gain at 700 kc s being not more than 6db down on that at 1 kc s Voltage Calibration The Y SHIFT control is calibrated from 2 0v to 2 0v in steps of 0 2v Shift and in RMS values 0 to 1 4v in steps of 0 1v RMS In conjunction with the attenuator this provides the following voltage ranges AC input impedance 1 MOhm 0 140v RMS 0 40v RMS 0 7v RMS 0 2v RMS 0 0 7 v RMS DC Input impedance 10 MOhm 0 2000 0 600v 0 200 0 60 v 0 20 v AC 50 c s only Input impedance 10 MOhm 0 7v RMS 0 20 RMS 0 70v RMS 0 400v RMS AIRMEC RADIVET MODEL 211 29 37 0 1400v RMS The accuracy of measurement is 10 Probes The following probes are permanently connected to the instrument and are stowed in compartments in the sides of the case when not in use RF Probe probe A forall Radio Frequency signal outputs Input Lead
11. to reset the scale by means of the trimmer C75 which is located in the right hand compartment of the case as shown in Fig 2 It is also desirable where freedom from drift is essential for instance when operating on the Long and Medium broadcast bands for the instrument to have been switched on for a period of at least twenty minutes The normal procedure for crystal calibration is as follows a Set the tuning dial accurately to the check point nearest to the frequency at which the instrument is to be used The check points at 2 5 mc s intervals are recommended for normal use Additional points which occur at very much reduced amplitude every 5 3 and 5 4 mc s are not reliable and should not be used unless their identity has been fully established Both scales are linearly AIRMEC RADIVET MODEL 211 PAGE 10 OF 37 calibrated in 1 mc s steps only whilst the number of kc s are read off the subsidiary scale which is calibrated at 10 kc s intervals and revolves once for every 1 mc s Reference should be made to Fig 4 which shows the tuning dials The example illustrated could be 4 425 5 9 425 5 14 425 5 89 425 mc s 94 425 mc s 99 425 mc s depending on the setting of the RANGE switch which determines which of the three scales is in use or the setting of the OUTPUT switch which determines whether 85 mc s is to be added to the scale reading Where a crystal check point coincides with a wanted frequency the
12. will normally be seen regardless of the AUDIO OSC frequency By checking the non linearity of the trace at each frequency from 40 c s to 15 kc s a thorough check can be made of the distortion characteristics of the amplifier If harmonic distortion is present the tips of the trace will bend towards the horizontal as shown in Fig 3g whilst overloading the amplifier will result in a trace similar to Fig 3f Severe overloading will cause both ends to bend sharply in the manner of Fig 3h If overloading is experienced before maximum rated output is reached possible causes are faulty supplies a low emission valve or faulty biasing conditions The output in watts may be determined by measuring the RMS deflection of the trace and calculating as follows Output voltage Wane Output voltage Loudspeaker impedance If the maximum output is too loud for continuous testing the loudspeaker should be replaced by a high wattage resistor of the same value If the trace opens into an ellipse as shown in Fig 3e the cause is phase shift between the input and output of the amplifier A horizontal or vertical ellipse denotes 90 phase shift and in other cases the phase angle may be found by carefully centralising the ellipse about the central point O as shown in Fig and measuring distances OP and OO The phase angle may then be calculated as follows Sinq 50 where q is the phase angle NB 180 phase shift will produce a str
13. 250 000 ohms Var R34 Adjust on test R76 330 000 ohms R35 1 000 000 ohms R77 22 000 ohms R36 A1522 100 R78 100 000 ohms R37 11 000 000 ohms R79 1 500 000 ohms R38 10 000 ohms R80 1 000 000 ohms Var R39 22 000 ohms R81 220 000 ohms R40 33 000 ohms R82 1 500 000 ohms R41 47 000 ohms R83 2 700 ohms R42 120 000 ohms R84 10 000 ohms AIRMEC RADIVET MODEL 211 PAGE 31 OF 37 TABLE 1 Contd SCHEDULE OF COMPONENTS Reference Description Reference Description R85 15 000 ohms R93 1 000 ohms R86 680 000 ohms R94 470 000 ohms R87 2 000 000 ohms Var R95 68 000 ohms R88 2 200 ohms Var R96 Adjust on test R89 1 000 ohms R97 39 000 ohms R90 33 000 ohms R98 1 800 ohms R91 47 000 ohms R99 Not used R92 1 000 ohms R100 Not used Cl 100 pf C33 1000 pf C2 1 500 pf C34 470 pf 2 2 pf 235 680 pf C4 470 pf C36 0 005 mf C5 47 pf C37 330 pf C6 47 pf C38 0 005 mf C7 16 5 pf Var C39 68 of C8 SPECIAL C40 01 mf 9 5 pf Var C41 3 3 pf C10 5 pf Var C42 22 pf C11 5 pf Var C43 68 pf C12 4 7 pf C44 01 mf C13 C45 01 mf C14 3 x 500 of C46 6 8 pf C15 Not used C47 4 mf C16 0 01 mf C48 01 mf C17 6 800 pf C49 470 pf C18 0 001 mf C50 3300 pf C19 100 pf C51 0 02 mf C20 0 001 mf C52 01 mf C21 100 pf C53 01 mf C22 0 05 mf 54 47 pf C23 80 mf 55 01 mf C24 22 56 22 pf C25 1500 pf 57 47 pf C26 20 mf 58 0 01 mf C27 05 mf C59 32 mf C28 470 pf C60 32 mf C29 0 001 mf C61 16 mf C30 0 005 mf C62 05 mf C31 3300 pf C63 6800
14. 40 c s to 15 kc s This is another exctasive feature which is nor marmally found even in expensive Standard Signal Generator i usefulness cannot be Over estialed since it enabies ne overall performance of any AM receiver to be checked over its complete audio frequency range insceac of at just one frequency AIRMEC RADIVET MODEL 211 PAGE 3 OF 37 The depth of modulation is 30 and great care has Leen taken to ensure that the spurious frequency modu tion is kept the very low level of tess chan 1 ke s Apart from modulation by means of the Audio Oscil later the Signal Generator can also be amplitude modu ated at the mains frequency of 50 c s FREQUENCY MODULATION The Audio Oscillator can also be used to Frequency modulate the outpuc signal over the same range of audio Frequencies The deviation under these conditions can be set to any value between O and 75 i e 0 to 100 modulation by means of the continuously variable Deviation Control on the front panel Normally the modulation level i e deviation is constant over the whole audio frequency range but by switching to Pre emphasis the modulation characteristic is adjusted to that of che B B C transmission This facility enables the same overall performance checks to be made on FM re ceivers as on AM receivers Furthermore the Output Signal can be frequency mod ulated with a wide deviation up to 250 ke s at the mains frequency of 50 c s This is
15. AIRMEC RADIVET MODEL 211 PAGE 1 OF 37 SPECIFICATION SIGNAL GENERATOR frequency Range Tuning Output Step Attenuators Variable Attenuator FREQUENCY MODULATION Frequencies Available Deviation AMPLITUDE MODULATION Frequencies Available Depth of Modulation Spurlous Frequency Modulation Combined Modufation CRYSTAL CHECK AUDIO OSCILLATOR Output Output Connection OSCILLOSCOTE RadlVet Type 211 0 5 Mejs 85 90 Mc s 5 10 Mc s 90 95 10 15 Me s 95 100 Mc s Tuning is by s single control with coarse and fine linear scales main scale is calibrated in only whilst the tubsidiary scale covers Mc s per revolution and is calibrated in 10 ke s divisions Maximum approximately 50 millivolts Minimum approximately microvo ts Seep attenuators in the RF probe and on the front panel provide ratios cf 1 10 1 100 and 1 1000 20 49 and 60 db control on the front panel provides a continuously variable attenuation over a 10 range 0 20 db 50 cfs Any frequency availabie from Audio Oscillator I 2 1 0 250 kc s at 50 2 0 5 75 kejs at Audio Oscillator frequencies 3 Pre emphasised signal has maximum deviation of 75 ke s available at 15 kc s Normal 8 8 C Pre emphasis of 50 micro seconds is provided As for Freguency Modulation Fixed at approximately 30 The maximum which can occur is kc s under any conditions Simu
16. TION control advanced The beat note will be seen to become localised at the centre of the trace into a small pip The frequency is now being swung at 50 c s in synchronism with the X plate scan and every time the frequency of the variable frequency oscillator is equal to that of a crystal harmonic this pip is produced This point on the trace must now be identified since the pip vanishes when the instrument is in normal use and in any case its retention would only serve to confuse the outline of any characteristic being traced To do this it is necessary to bring the pip exactly under the vertical graticule using the X shift control Thereafter the point on the trace that appears under this graticule is at the frequency shown on the dial The GAIN amp OUTPUT switches may now be returned for normal usage It is assumed in all the AIRMEC RADIVET MODEL 211 PAGE 11 OF 37 following instructions that the freguency calibration check has previously been carried out 2 3 HF Signal Generator 2 3 1 Un modulated The signal generator freguency should be set up as indicated in Section 3 2 above and Probe A RF should be connected to the point at which the signal is reguired using the shortest possible connecting leads The maximum output level is 50 milli volts with the OUTPUT control fully clockwise and the probe flying lead in the X1 socket This may be reduced to 5 milli volts or 500 micro volts by plugging
17. Tunethe receiver to 1 25 mc s until the RadiVet signal is heard If the RadiVet is now tuned through the freguency range 100 kc s to 1 25 mc s a signal will be heard at each of following freguencies 125 139 156 3 178 6 208 3 250 301 25 416 6 and 625 kc s Once the positions of these spot freguencies on the RadiVet tuning dial have been determined any of them may be used for the alignment procedure For instance if the manufacturer specifies alignment at 100 kc s and 600 kc s the 125 kc s and 625 kc s signals could be employed 4 3 Overall Check This test is an extension of Sect 5 2 and the RadiVet should be connected as tabulated for that section Set the TUNING control to the reguired freguency and switch the AUDIO OSC from 40 c s to 15 kc s The output amplitudes at each freguency should be noted and plotted to illustrate the overall freguency response of the receiver 5 AUDIO AMPLI FI ERS The tests outlined in Sect 6 1 amp 6 2 can be applied to any audio amplifier either as a whole or to an individual stage The AF stages of commercial receivers are not normally subjected to rigorous response checks but where the overall performance of a receiver is indifferent due perhaps to a lack of either treble or bass response overall distortion and response tests can be informative Detailed information on the response of audio stages is not normally given in the servicing instructions but it will be found that the audio stages
18. accuracy will be 0 01 but between check points the accuracy will be better than 40 kc s Set the OUTPUT switch to XTAL CHECK the GAIN switch to INT CHECK and the FM and AM switches to OFF The X PLATES switch may be at 50 c s or any of the four TB ranges but not at VAR FREQ since the audio oscillator is operating as an amplifier for this facility Rotate the trimmer C75 the location of which is shown in Fig 2 until a deflection is obtained on the Y axis of the crt The amplitude of the deflection may then be adjusted to a convenient height by means of the RF OUTPUT control As the trimmer is adjusted through the correct tuning point the amplitude of the deflection will gradually rise to a maximum and then suddenly fall to zero If adjustment is continued in the same direction the amplitude will rise equally suddenly and will then gradually fall off again The correct setting is at the zero beat between the two amplitude peaks but it must not be expected that this position will be completely stable and it will be sufficient if the beat is obviously of an audio frequency When the OUTPUT and GAIN switches are returned to the required setting the correct output frequency will be obtainable at Probe A RF probe When the wobbulator facility is required the above adjustment should be made but before altering the setting of the GAIN and OUTPUT switches the FM switch and the X plate switch should be set to 50 c s and the DEVIA
19. ages great care must be taken to ensure that the signal input level is always less than that necessary to operate the limiter After each trimmer has been adjusted check that a slight reduction in the RadiVet output does in fact reduce the amplitude of the crt display If this is not so reduce the RadiVet output accordingly and re check the trimmer setting 3 5 Overall check and de emphasis 100 modulation on the existing BBC system refers to 75 kc s deviation With the pre emphasised transmission characteristic of 50 micro seconds which is used the modulation signal level which is necessary to provide 75 kc s deviation at 15 kc s will only provide 14 kc s deviation at 40 c s and this accent on the higher frequencies has to be eliminated by the de emphasis circuit on the receiver In order to check that this de emphasis is being correctly applied in the receiver the RadiVet can be frequency modulated with the correct pre emphasis characteristic by setting the FM switch to VAR OSC PRE EMPHASIS Probe or switch Connection or setting RF Aerial input at point stated service data sheets Probe B Audio Not used Probe C Oscilloscope Loudspeaker terminals FM VAR FREQ PRE EMPHASIS DEVIATION Maximum fully clockwise AM OFF AUDIO OSC Frequency required see text GAIN AC position as required to prevent overloading the Y amplifier AIRMEC RADIVET MODEL 211 18 37
20. aight trace inclined from top left to bottom right of the crt 5 2 Overall response check Connect the RadiVet as tabulated Sect 6 1 and with the X PLATES set at 50 c s or any of the TB positions measure the amplitude of trace deflection on the crt at each frequency from 40 c s to 15 kc s If these results are plotted they will illustrate the overall response characteristic of the amplifier AIRMEC RADIVET MODEL 211 21 37 If the characteristic has unexpected falling tendency at either end or in the middle the position of any tone control should be checked If their setting is not the cause of the unusual characteristic examine each audio stage individually until the cause of the fault is located 6 TESTS ON TAPE RECORDERS The RadiVet is extremely useful for assessing the performance of setting up and locating faults in magnetic tape recorders When manufacturers instructions or service data sheets are available they should be followed as closely as possible The following instructions are intended to supplement those given for any particular machine and in the absence of any specific servicing data they will serve as a guide to the procedure which should be adopted 6 1 Bias The bias waveform must be completely free from distortion or noisy recordings may result The bias frequency is less important it usually lies between 40 kc s and 60 kc s and quite wide latitude is permissible Incorrect bias a
21. all characteristics Connect Probe B to the record input terminals and record a length of tape at each playing speed as follows At an input frequency of 400 c s adjust the record level to slightly less that one half of its correct value and then record all freguencies from 40 c s to 15 kc s Tabulate freguency against footage indicator readings Play back each length of tape measuring the output amplitude at each frequency by means of the valve voltmeter facility and tabulate the results of output against footage indicator readings Combine these two sets of figures to give a table of output amplitude with reference to input freguency and plot the curve The play back characteristics should in general have a level freguency response as follows Approximately 40 c s to 5 kc s at 3 ips tape speed 40 c s to 12 kc s at 732 ips tape speed 40 c s to 15 kc s at 15 ips tape speed 6 4 Wow Flutter and Tape Drop out Record a length of tape at 400 c s with Probe B connected to the input terminals and the AUDIO OUTPUT and record level controls adjusted to give the correct level Play back the recording and examine the output both aurally and by means of the oscilloscope facility of the RadiVet If the recorder suffers from wow or flutter the note will be heard to vary in frequency and the synchronisation on the oscilloscope will be erratic If this is so the capstan should be checked for eccentricity Rand
22. an amplifier when the crystal calibration facility is used The output from V3b is applied to the Y Amplifier when the GAIN switch is in the INT CHECK position and the beat freguency appears on the crt screen The amplitude of this beat note is dependent upon the setting of the RF OUTPUT control 9 SPECIFICATION 9 1 RF Signal Generator Freguency Range The tuning range is 0 15 5 and 85 100 mc s in six bands 0 5 5 85 90 5 0 10 5 90 95 5 10 15 mc s 95 100 5 Tuning Tuning is by a single control with coarse and fine linear scales The main scale is calibrated in mc s only whilst the subsidiary scale covers 1 5 per revolution and is calibrated in 10 kc s divisions Output The maximum output is approximately 50mv Step Attenuators Step attenuators in the RF probe and on the front panel provide ratios of 1 10 1 100 and 1 1000 20 40 6000 Variable Attenuators control on the front panel provides continuously variable attenuator over a 10 1 range 0 2000 Frequency The frequencies available are 50 c s or any frequency available from Modulation the Audio Oscillator The deviation obtainable is 0 to 250 kc s at 50 c s or 0 to 75 kc s at Audio Oscillator frequencies A pre emphasised signal having a maximum deviation of 75 kc s at 15 kc s and having normal BBC pre emphasis of 50 microseconds is provided Amplitude Modulation Amplitude modulation to a fixed depth of appr
23. arried out on Public Address eguipment tape decks and AM broadcast receivers Basically the RadiVet consists of three independent instruments housed in one case an AM FM signal generator with crystal calibration an audio oscillator and an oscilloscope These three instruments which can be used either separately or in conjunction one another enable every function of a receiver to be thoroughly investigated The interconnections required for the different tests are set up by means of switches on the front panel A brief summary of the facilities of the RadiVet is given in Section 2 from which an experienced service engineer will be able to work out his own methods of employing the instrument Full instructions for operating the RadiVet to obtain each of the facilities are given in Section 3 and the application of these facilities to testing FM and AM receivers audio amplifiers tape recorders and television receivers are dealt with in Sections 4 to 8 A detailed technical description of the circuit appears in Section 9 a specification in Section 10 and maintenance instructions in Section 11 1 SUMMARY OF FACILITIES The facilities provided by the RadiVet are listed below and further information on voltage ranges accuracy etc is given in Section 10 Signal Generator The signal generator covers the frequency ranges 0 to 15 mc s and 85 to 100 mc s that is the normal broadcast AM band and FM IF band and the FM transmission band The outp
24. be measured by means of the Y attenuator and calibrated Y shift control The input impedance is high as in the case of DC measurements and the instrument therefore operates as an AC valve voltmeter at 50 c s and audio frequencies 1 6 Frequency Calibrator The instrument contains a 5 mc s crystal oscillator that may be used to calibrate the output frequency to a very high degree of accuracy 1 7 Suitability for AC DC receivers The chassis and earth line of the RadiVet are isolated from earth and from the case and the instrument may therefore safely be used with AC DC sets where the chassis may be live relative to earth 2 OPERATION 2 1 1 nitial Adjustment The RadiVet is supplied complete and ready for use All probes are permanently connected and a mains lead is provided to which a plug should be connected The red black and green leads are live neutral and earth respectively and it is important that the earth lead should be connected to ensure correct screening The RadiVet is despatched with the mains tapping panel set for operation on 230 volt supplies If operation on supplies of different voltage is required the fused plug on the tapping panel which is accessible inside the right hand probe storage aperture should be moved to the required tap 2 2 Frequency Calibration If the full accuracy of the frequency calibration of which the RadiVet is capable is to be realised it is necessary before use
25. e of a triode oscillator The anode circuit L7 is tuned to 65 mc s that is the 13th harmonic of the crystal A certain amount of regeneration takes place via C57 L7 is normally tuned with circuit stray capacitance but when the OUTPUT switch 54 is in either of the 85 mc s positions L7 is shunted by C76 so that it tunes to 20 mc s that is the fourth harmonic of the crystal When the OUTPUT switch is in the central position XTAL CHECK the damping resistor R25 flattens the tuning of L7 so that preference is not given to any crystal harmonic The output of the variable frequency oscillator 65 80 mc s therefore appears at the anode of the crystal harmonic amplifier together with either of the following Preferred 13th harmonic 65 mc s NORMAL b All crystal harmonics XTAL CHECK c Preferred 4th harmonic 20 mc s 85 mc s These added outputs when fed to the mixer valve V2b will result in the following a VFO minus crystal 65 mc s giving 0 15 mc s in three ranges 0 5 5 10 and 10 15 mc s b Each crystal harmonic from the 13th to the 16th will produce an audio beat at 5 mc s intervals so that the frequency of the VFO may be checked at 5 mc s intervals Additional beats may be found at 2 5 mc s or even 1 667 mc s and 1 25 mc s intervals due to the second third and fourth harmonics of the VFO beating with higher order harmonics of the crystal VFO plus crystal 20 mc s giving 85 100 mc s in th
26. en th tuning knob and tuning The secand requirement is fulfilled by incorporating a crystal calibrator which i described in detail below CRYSTAL CALIBRATION 5 Mc s Civseal Calibrator accurate to 0019 is in corporated which enables check points to tz established at the top and bottem of each the six recuanry ranges addition a sub harmonic at 2 5 Mc s gives a check point at the centre of each range Considerable care has been taken in the design of the calibrator to make it a simple as possible to use The tuning dial is first sec at the nearest check poirt to tive wanted frequency and a calibrate knob adjusted unul zero beat note appears on the screen The tuning control then be turned until the required frequency is indicated and the signal generator wil be set to that frequency with very high accuracy The extreme simplicity of this operation is made pos sible by the unusual tuning system which gives a com pletely linear scale between the crystal check peinc or each range Once the generator is standardised at check point theretore the direct calibration holes fer alt frequencies within 1 25 Mc s on either side thac i half way to the next check point and no arithmetical calculation is needed for interpolation AMPLITUDE MODULATION The Signal Generator can be amplitude moduisted means of duiit in oscillator at frequencies throughout the entire audio range from
27. f a normal AM receiver IF filter 1 2 Audio Oscillator An audio oscillator providing a choice of eleven fixed freguencies between 40 c s and 15 kc s is incorporated in the RadiVet This oscillator may be used for amplitude or frequency modulation of the RF oscillator as an audio output signal for tests on audio equipment and tape recorders and to scan the X axis of the cathode ray tube AIRMEC RADIVET MODEL 211 PAGE 9 OF 37 1 3 Oscilloscope The crt has an associated DC coupled Y amplifier and time base The frequency response extends from DC up to 1 mc s and in conjunction with the saw tooth time base generator provides a useful oscilloscope for general waveform investigations The Y attenuator is calibrated and in conjunction with a calibrated Y shift control enables the amplitude of any observed waveform to be measured 1 4 DC valve voltmeter The cathode ray tube calibrated Y attenuator and calibrated Y shift control form a DC valve voltmeter which enables voltages to be measured without placing an appreciable loss on the circuit This is particularly useful when measuring the potentials of valve electrodes where an appreciable current drawn by the measuring instrument can completely change the voltage and provide very misleading results 1 5 AC Valve Voltmeter As mentioned in the paragraph dealing with the oscilloscope facility above the amplitude of a waveform displayed on the crt may
28. h Probe C connected to any required point between the sound detector and the loudspeaker The audio circuits can of course be checked as detailed in Sects 6 1 and 6 2 7 3 Time base checks Since the frequency response of the Oscilloscope Y amplifier extends to at least 1 mc s line and frame time base waveforms may be examined without introducing any appreciable distortion by connecting Probe C to the required point and setting the GAIN switch to the AC position which gives a display of reasonable amplitude The waveform be resolved by switching the X PLATES to one of the TB positions as required and adjusting the TB VEL FINE control until a satisfactory display is obtained 8 DESCRIPTION OF Ci RCUIT 8 1 General The circuit diagram of the instrument is shown in Fig 1a 1b in the appendix and the list of components in Table 1 Figure 2 shows the location of the major components The circuit consists essentially of a signal generator audio oscillator oscilloscope and crystal calibrator and each of these basic units is described in turn below AIRMEC RADIVET MODEL 211 25 37 8 2 RF Signal Generator The double triode valve V1 forms the variable frequency oscillator One half is the reactor valve 1 and the other half is the tuned anode oscillator The basic range is 65 70 mc s Two other ranges are obtained by means of the RANGE switch S7 which connects shunt inductors and capacitors to gi
29. he tuning control will appear accurately under the vertical centre of the graticule As the tuning control is rotated therefore the picture will move along so that any particular part of the trace may be placed under the vertical line and the frequency measured Bandwidths may be determined by measuring the frequency of the two ends of the response and taking the difference Accurate frequency calibration may be obtained by checking with the crystal calibrator as described in Sect 3 2 By suitable adjustment of the RF OUTPUT and the Y SHIFT controls the trace be positioned so that it lies between the 0db and infinity horizontal lines on the graticule as shown in Fig 5 The level at any particular frequency may then be measured by reference to the db scales on the cursor two of which are provided since the trace may be inverted 2 6 Oscilloscope The oscilloscope may be used to observe repetitive waveforms over a frequency range of approximately 30 c s to 1 mc s Probe C should be connected to the point at which the waveform is available and the earth clip connected to a convenient point on the chassis The OUTPUT switch may be in any position other than the XTAL CHECK and the Y GAIN switch should be at one of the AC positions the position being selected to provide reasonable amplitude on the crt The X PLATES switch should be turned to one of the four positions The position chosen will depend on the freque
30. ignal to the equipment under test The frequency response of the filters or discriminators will produce an amplitude modulated output from this frequency modulated signal and the amplitude modulation may be used to provide a picture of the receiver s frequency response over the sweep frequency range The amplitude modulation must first be rectified in the receiver and this is dealt with in Sections 4 1 and 5 1 In the case of an FM receiver this involves making the discriminator ineffective The rectified output is taken from the audio section of the receiver via Probe C and fed via the Y amplifier to the Y plates of the crt X plates are connected to the modulating frequency in this case 50 c s and the figure obtained on the crt represents response plotted against frequency The procedure to operate as a wobbulator is therefore to adjust the signal generator as described in Section 3 3 3 but with the FM switch at 50 c s The X plates switch should be turned to 50 c s and the DEVIATION control adjusted to provide the required amount of sweep maximum corresponding to about 500 kc s The Y GAIN switch should be turned to one of the AC positions the position being chosen to give a picture of reasonable amplitude The FOCUS BRILLIANCE and the Y SHIFT controls should be manipulated to obtain a satisfactory picture The horizontal deflection of the trace represents frequency and the frequency as set up on t
31. ime Base Generator valve V5a Valve V4b which is the X amplifier is DC connected to the crt X1 plate A variable DC voltage derived from the X SHIFT control R71 is fed to the X2 plate V4b may be fed from one of the three sources selected by the X PLATES control S3 They are a 50 c s b Variable AF from the audio oscillator Saw tooth waveform of variable frequency from the Time Base Generator valve 5 V5a is a clocking oscillator and T2 is the blocking transformer Four frequency ranges may be selected by means of S3 and the frequency of each range can be varied continuously by adjustment of the resistive element of the grid discharge constant R87 TB VEL FINE Synchronising signals are fed to the cathode across R88 AIRMEC RADIVET MODEL 211 27 37 Fly back suppression the four time base ranges is applied to the crt grid via C54 To avoid confusion when the 50 c s X scan is used it is preferable for only one trace either the forward or the re trace to appear on the crt screen Therefore a small 50 c s signal phase shifted 90 by the components C68 R95 C69 and R81 is fed to the grid of the crt so that the forward trace is brightened and the re trace is blacked out 8 5 Crystal Calibrator With the OUTPUT switch at XTAL CHECK the output from the variable frequency oscillator is mixed with harmonics of the 5 mc s crystal and the mixed output is fed to the grid of V3b which functions as
32. ing noted The difference between the two readings multiplied by the GAIN setting gives the voltage For example First Reading 0 1v Second Reading 0 9v Difference 1 0v GAIN setting x30 Voltage 10 30 30v 2 8 Valve Voltmeter AC 2 8 1 Voltage below 400 peak to peak The connections are the same as for the preceding Section 3 7 except that it is not necessary first to check the zero setting Measurement may be made at freguencies between 30 c s and 100 kc s and at freguencies up to 500 kc s with reduced accuracy using the following switch positions 0 7v RMS ACx 1 2 0v RMS 3 7 0v RMS ACx 10 40v RMS ACx 30 140v RMS AC x 100 O OOOO First move the trace with the Y SHIFT VOLTS control so that its top is coincident with the central horizontal graticule and note the reading of the INNER scale Then move the trace until its bottom is coincident with the central horizontal graticule and note the new reading Add the two readings together ignoring the ve and ve signs and the result multiplied by the GAIN switch setting is the RMS value of the voltage For example First reading 0 6v Second reading 0 6 Switch setting AC x 100 Voltage 0 6v 0 6v x 100 1 2 x 100 120v AC RMS AIRMEC RADIVET MODEL 211 PAGE 14 OF 37 2 8 2 50 c s Voltage above 400 peak to peak In addition to the AC readings dealt with in Section 3 8 1 higher
33. l reduce AM at all frequencies and will eliminate it at the frequency at which the currents in the two diodes are equal Discriminators however afford no appreciable AM rejection and are usually preceded by a low level limiter stage The efficiency of the AM rejection can be assessed by means of the response curve which will be obtained when the RadiVet is connected as tabled above The curve will appear as shown in Fig 3 b or 3 c It can be seen that there is one point on each curve where AM rejection is complete but in Fig 3 c this occurs at the incorrect tuning point Any receiver which presents a response curve of this type would be liable to interference of amplitude modulated form motor ignition un suppressed motors etc even when correctly tuned for minimum distortion and in the case of a ratio detector maximum output The cause of such a characteristic is differing AF paths for the two diodes Some manufacturers insert small resistors in series with each diode load so that one or the other may be short circuited to bring the circuit nearer balance In some receivers these adjustable resistors may take the form of a potentiometer with earthed slider inserted in series with the bias load If no such adjustment is provided one or both of the diode load resistor values maybe outside the limits laid down in the service manual The resistors should be checked and if necessary replaced In extreme cases the fault may be due to an out
34. ltaneous fregucncy and amplitude modulation can be applied to all ranges for checking by means of Wobbulator display that limicers and ratio detectors are limiting correctly 5 Mejs crystal oscillator is provided to enable the main oscillator fre quency to be set accurately The accuracy obtainable is Better than 0 01 for any harmonic or sub harmonic of 5 Mc s Better than 40 kc s for all other frequencies This is of the Resistance Capacity coupled type and has I switched output frequencies of 40 60 90 150 and 400 1 3 5 8 12 and 15 kejs The maximum output available i approximately 20 and this can be reduced to minimum of approximately 5 millivolts by means of a control on the front panel The output from the Audio Oscillator can be used the following manner 1 As test signal for L F stages Available on audio lead 2 To frequency modulate the R F output on ail ranges with deviation variable between 0 and 75 ke s 3 To Amplitude Modulate the output on ranges to a depth of approximately 30 4 To simultaneously Araglitude and Frequency Modulate the R F output on all ranges The built in Oscilloscope uses a 2 Cathode Ray tube and focus and brilliance controls are provided Continued everleuf AIRMEC RADIVET MODEL 211 PAGE 2 OF 37 RADIVET has been designed and built with the busy service engineer in mind and is a very cornpact piece of te
35. modulate the RF signal applied to or ratio detector is unhalonced the RF or stages AIRMEC RADIVET MODEL 211 PAGE 5 OF 37 _ from audio aseillotor is fed directly to the and through a distortionless amplifier to the la a like manner the frequency response and phase and harmonic distortion characteristics of a co FM re eeiver or any stage of it can be checked by uting the Audio Oscillator to Frequency Modulate the RE signal pled te tha RF or IF stages Finally the de emphasis circuits provided in all EM re can be tested by switching to F M with froe emphasis when as mentioned above circuit giving the correct 50 microseconds Pre cmphatis as specified by the BBC is switched in The modulated signal may be fed isto the receiver via either the R F or the LF stages and the output monitored on the Oscilloscope If the deemphasis circuits are operating 3 constant output ac all frequencies should be obtained Figure 5 h Waveform obtained as in when the amplifier introducing hurmonic distortion Figure 5 Waveform obtained as in when the amplifier is introducing phase distortion only OSCILLOSCOPE The self contained built in Oscilloscope employs a 2 Cathode Rsy tube giving a display of sufficient size and clarity for general purpose servicing work Brilliance and Focus Control are provided and automatic flyback sup prenion on the Time Base
36. mplitude can cause distortion low output and poor signal noise ratio 6 1 1 Bias Waveform Use the oscilloscope facility of the RadiVet and connect Probe C to the bias supply point of the record head Any distortion of the bias oscillator waveform should be remedied until a pure waveform is obtained A common cause of distortion is over driving the bias oscillator valve and if distortion is apparent this possibility should be examined before more complex measurements are made 6 1 2 Bias Frequency Use the oscilloscope facility of the RadiVet with the X PLATES switch set to VAR OSC Under these conditions a Lissajou pattern Fig 7 will be obtained and the AUDIO OSC switch and the recorder bias frequency control should be adjusted in conjunction with each other until the pattern is stationary By cross reference between the pattern and the table below the exact frequency of oscillation can be determined and hence the oscillator adjusted to the nearest frequency to the one specified in the instructions Bias Frequency Loops AUDIO OSC Frequency 40 5 8 42 2x7 12 44 2 x 11 8 45 3 15 48 4 12 50 10 5 52 2x13 8 54 2x9 12 56 7 8 60 4 15 6 1 3 Bias Amplitude The correct level of bias is usually specified as being a level slightly greater than that required to obtain the maximum output for a given signal input If the required level is known the bias level can be measured using the AC valve voltme
37. ncy modulated at 50 c s or any of the audio oscillator frequencies 0 30mc s in 3 x 10 mc s bands This is the 2nd harmonic of the 0 15 mc s FM or AM range 65 80 mc s in 3x5 mc s bands Output switch to 85 mc s The level of signal is FM only greater than that of the normal output ranges 195 240 5 3x 15 mc s bands Output switch to 85 5 This is the 3rd harmonic of the 65 80 mc s range but it may be of sufficient amplitude to be of use on Band lll receivers In all cases provided that calibration adjustments are carried out as specified in Sect 3 2 these ranges are of the same high order of frequency accuracy as the normal output range of the RadiVet 7 1 Alignment of vision channel Connect Probe A to the required signal injection point of the receiver and with Probe C connected to some point between the vision detector and the modulating electrode of the crt carry out the aligning procedure as detailed in the service data sheets When amplitude modulated signals are injected the AC Valve Voltmeter facility should be used to monitor the amplitude of signal received at the vision amplifier whilst if un modulated signals are injected the DC Valve Voltmeter facility should be used to measure the changes in DC level caused by signal injection and trimming adjustment 7 2 Alignment of sound channel Spot frequency alignment using amplitude modulated signals only may be carried out as in Sect 8 1 but wit
38. ncy of the signal being observed and should be the one that enables a steady picture to be obtained at some position of the TB VEL FINE control When a steady waveform of reasonable amplitude is obtained adjust the BRILLIANCE and FOCUS controls to obtain a sharp trace and centralise the display by means of the X shift and Y shift controls 2 7 Valve Voltmeter DC Voltage measurements be made by means of the crt the calibrated Y attenuator and the Y shift control When making measurements on AC DC receivers care should be taken to ensure that AIRMEC RADIVET MODEL 211 PAGE 13 OF 37 Probe A and B are not stowed or located in any position where the leads may short circuit to earth or be a danger to personnel The X PLATES switch should not be switched to VAR OSC if the OUTPUT switch is at XTAL CHECK With Probe short circuited set the trace on the central horizontal graticule with the Y SHIFT VOLTS control and note the outer scale reading of the Y SHIFT control Set the GAIN switch to the desired DC range as follows 20 DCx 10 60 DCx 30 200 DCx 100 600v DCx 300 2000v DC x 1000 DC O O O O O Connect Probe C to the point at which the voltage is to be measured A deflection of the trace upward for a positive voltage and downward for a negative voltage will be observed The trace should be brought to the central line with the Y SHIFT VOLTS control and the read
39. nd of the tuning scale as detailed in Sect 3 2 and if the adjustment of the CALIBRATION control C75 is inadeguate C9 should be adjusted see Fig 2 with C75 at the centre of its traverse No attempt should be made to adjust the linearising capacitor C8 without special eguipment AIRMEC RADIVET MODEL 211 PAGE 30 OF 37 TABLE 1 SCHEDULE OF COMPONENTS Reference Description Reference Description R1 100 ohms R43 470 000 ohms R2 680 ohms R44 470 000 ohms R3 4 700 ohms R45 100 000 ohms R4 20 000 ohms Var R46 68 000 ohms R5 4700 ohms R47 33 000 ohms R6 39 000 ohms R48 Not used R7 220 000 ohms R49 15 000 ohms R8 1 000 000 ohms R50 47 000 ohms R9 15 000 ohms R51 47 000 ohms R10 100 000 ohms R52 68 000 ohms R11 68 000 ohms R53 2 500 ohms Var R12 330 ohms R54 3 900 000 ohms R13 330 ohms R55 4 700 000 ohms R14 680 ohms R56 620 000 ohms R15 10 000 ohms R57 220 000 ohms R16 1 500 ohms R58 68 000 ohms R17 Not used R59 22 000 ohms R18 Not used R60 10 000 ohms Var R19 100 ohms R61 220 000 ohms R20 10 ohms R62 1 500 000 ohms R21 60 000 ohms R63 680 ohms R22 50 000 ohms Var R64 22 000 ohms R23 220 000 ohms R65 100 000 ohms R24 220 000 ohms R66 6 800 ohms R25 1 000 ohms R67 1 000 000 ohms R26 470 000 ohms R68 100 000 ohms R27 220 000 ohms R69 150 000 ohms R28 750 ohms R70 150 000 ohms R29 750 ohms R71 250 000 ohms R30 82 ohms R72 100 000 ohms R31 82 ohms R73 120 000 ohms R32 12 000 ohms R74 330 000 ohms R33 390 ohms R75
40. nt and arc stowed in compartments ia the side of the case When ysg gt RF Prebe or Frequency signal outputs input 1000 07 all AC and inputs to the oscilloscope Audio Lead for all Audio Frequency outputs VALVES off DGP off I 12 7 4 off EARTHING As the chassis is Hohted from the maine rth universal receivers may be checked without dificylty POWER SUPPLIES The Instrument operates from supplies of 100 130 and 200 250V at 40 49 the consemption being approximately 45 watts The mains lead is perma ently connected to the instrument and con de slowed with the probes when the instrument is being transported DIMENSIONS The overall dimentions sre 1517 ong x H deep and Bi high F4 x MA x 214 FINISH The cate is in dark grey hamicr finish stove enamel and the front panel in ht grey gion WEIGHT The total weight of the unit it approximately 27 the 1127 kg This specification is representative of an average instrument and we reserve the right to affect modifications AIRMEC LIMITED HIGH WYCOMBE BUCKINGHAMSHIRE ENGLAND Telephone High Wycombe 2501 10 lines Cables Atrmec High Wycombe AIRMEC RADIVET MODEL 211 PAGE 8 OF 37 INTRODUCTION The RadiVet has been designed and built primarily as a very compact piece of test gear for checking aligning and locating faults in all stages of FM receivers The facilities provided also enable tests to be c
41. of balance condition of diode impedance caused by one diode losing emission or the use of unmatched crystal diodes AIRMEC RADIVET MODEL 211 PAGE 17 OF 37 3 4 RF alignment Since there is considerable variation in the manner in which the RF circuits of FM receivers are tuned the specific alignment instructions in the manufacturers service data sheets must always be followed Probe or Switch Connection or Setting Probe A RF Aerial input or at point stated in service data sheets Probe B Audio Not used Probe Oscilloscope Input to 1 AF stage FM VAR FREO NORMAL DEVIATION As reguired see text AM OFF AUDIO OSC Frequency required Say 1 kc s GAIN AC Position as required to prevent overloading of Y amplifier X PLATES 50 c s or any ofthe four TB ranges TUNING Required alignment frequency RF FREQ RANGE 85 mc s Normal or 20 db as required OUTPUT As required See text Using the above connections adjust all trimmers etc as laid down the servicing instructions The amplitude of signals on the crt should be adjusted as required by the setting of the GAIN switch and the receiver volume control The setting of the DEVIATION control will also affect the amplitude of the crt display but this control should be set as required by the service data sheets Maximum deviation of 75 kc s is obtained when the control is fully clockwise When aligning RF st
42. oint providing no faults exist in the receiver a trace similar to that shown in Fig 3a will be obtained The portion of the trace which crosses the horizontal axis will generally be linear and the two humps of opposite polarity should be egual in amplitude When the alignment is correct the vertical graticule which corresponds to the exact IF will bisect the horizontal distances between the two humps Should the servicing data call for a specific bandwidth between either extremities of the linear portion of the response or the two humps the bandwidth may be measured by noting the scale readings when one and then the other limit reguired is placed under the vertical graticule The bandwidth is the difference between these two readings 3 3 AM Rejection Probe or Control Connection or Setting Probe A RF Signal grid of freguency changer Probe B Audio Not used Probe Oscilloscope Live side of volume control FM 50 5 DEVIATION Maximum fully clockwise AM VAR FREQ AUDIO OSC Any suitable frequency say 3 kc s GAIN AC X1 X PLATES 50 5 e RANGE Receiver intermediate frequency as required OUTPUT Minimum possible consistent with reasonable deflection on crt trace AM rejection is achieved in most receivers by limiter action but when the incoming signal is below the limiter threshold value and a ratio detector is in use some additional AM rejection is afforded Ratio detectors wil
43. om variations in amplitude sometimes known as drop out will be immediately apparent from the above The cause is almost always a faulty tape and the imperfect section should be excised 6 5 Tape slip Record a length of tape as in Sect 7 4 but at a low frequency say 60 c s Play back this recording and monitor the output using the oscilloscope facility with the X PLATES set at VAR OSC and the AUDIO OSC at 60 c s An almost stationary ellipse should be obtained Any sudden change in the location of the ellipse is due to tape slip which is generally caused by inadequate pressure from the pinch roller 7 TESTS ON TELEVI SI ON RECEIVERS The TeleVet Type 877 is designed solely for testing television receivers and the RadiVet is a complementary instrument which was not designed for this purpose The RadiVet can however provide a number of useful facilities in this direction A large number of manufacturers instruction sheets specify the spot frequency method of alignment and outputs in the following ranges can be obtained from Probe A at an amplitude of approximately 50mv 0 15 5 3x 5 5 bands 45 60 5 in3x5mc s bands Output switch to 85 5 The two above ranges can be amplitude modulated at 50 c s or with any of the audio oscillator frequencies if required AIRMEC RADIVET MODEL 211 24 37 The following ranges of weaker signals can be obtained either un modulated or freque
44. or with preferred harmonics from a 5 5 crystal oscillator alternative output frequencies of 15 to 20 and 20 to 25 mc s are present at Probe A when the RANGE switch is set at 10 to 15 5 For 15 to 20 mc s use the 5 to 10 mc s scale and for 20 to 25 mc s the 10 to 15 mc s scale each case add 10 mc s to the scale setting Signals in the band 15 to 20 mc s are approximately 12 db below the main output signal levels and the amplitude of the signals in the 20 to 25 mc s band is of course still lower No reduction in accuracy is entailed when these higher output frequencies are used When called for in the service manual the local oscillator of the receiver should be rendered inoperative this can usually be effected by connecting the oscillator grid to earth AIRMEC RADIVET MODEL 211 15 37 Remove the core from the secondary tuned circuit of the discriminator or the ratio detector with the RadiVet connected as above adjust all the IF cores for maximum dellection of the crt trace Should the initial signal level be insufficient due to a receiver fault it may be increased by disconnecting the RF tuned circuit from the signal grid of the frequency changer but this should not normally be necessary The level of the signal on the crt trace can be increased by connecting Probe C to some point further along the AF amplifier chain e g the grid of the power output stage whilst any necessary reduction of the t
45. ould be obtained Correct limiter action will be shown by a flattening of the peak of the response curve when the input signal is increased beyond the limiter threshold level 3 2 Discriminator Ratio Detector Response For this operation service manuals may again call for either the Spot frequency or the Wobbulator method of alignment The latter method is to be preferred however since it offers a simultaneous check of correct alignment and linearity 3 2 1 Spot frequency alignment Probe connections and control settings required are those tabulated for Section 4 1 1 The RadiVet OUTPUT control should then be adjusted until the signal input is just less that that necessary to operate the limiter i e deflection still increases with increased input If the core of the discriminator or ratio detector secondary coil is replaced and screwed in the deflection of the crt trace will rise to a peak decrease slightly rise to a further peak and then return to zero The core is correctly adjusted when the bottom of the trough between the two peaks is reached When the receiver is fitted with a tuning indicator the correct core position will generally coincide with an indication of correct tuning AIRMEC RADIVET MODEL 211 PAGE 16 OF 37 3 2 2 Wobbulator Alignment Connect the RadiVet as tabled in Section 4 1 2 and replace the core of the discriminator or ratio detector secondary coil As the core is screwed in at some p
46. oximately 30 is available at the same frequencies as for frequency modulation see above The maximum spurious FM occurring with AM is 1 kc s Simultaneous frequency and amplitude modulation can be applied to all ranges Crystal Check A 5 mc s crystal oscillator is provided to enable the main oscillator frequency to be set accurately The accuracy obtainable is Better than 0 01 for any harmonic or sub harmonic of 5 mc s Better than 40 kc s for all other frequencies AIRMEC RADIVET MODEL 211 28 37 Audio Oscillator This is of the thermistor controlled Resistance Capacitance coupled type and has 11 switched output frequencies 40 60 90 150 and 400 c s 1 3 5 8 12 and 15 kc s The maximum output available is approx 2 0v peak to peak and this can be reduced to a minimum of approximately 5mv peak to peak by means of a control on the front panel The output from the audio oscillator can be used in the following manner a As test signal for LF stages Available on probe b To frequency modulate the RF output on all ranges with a deviation variable of between 0 and 75 kc s c To amplitude modulate the RF output on all ranges to a depth of approximately 30 d To amplitude and frequency modulate the RF output simultaneously on all ranges Cathode Ray Tube The built in oscilloscope uses 232 cathode ray tube and focus and brilliance controls are provided Time Base The hard valve
47. race amplitude should wherever possible be effected by reduction of the signal input level Correct limiter action will be shown by a decreased deflection for an increased signal input beyond the limiter threshold level For this check it will generally be necessary to set the GAIN switch to some higher attenuation value than X1 in order to prevent overloading the Y amplifier 3 1 2 Wobbulator Alignment Probe or Control Probe A RF Connecting or Setting Signal grid of freguency changer Probe B Audio Not used Probe C Oscilloscope Live side of volume control FM 50 5 DEVIATION Maximum fully clockwise AM OFF GAIN X1 X PLATES 50 c s TUNING RF Frequency Range Receiver intermediate frequency as required Minimum possible consistent with reasonable OUTPUT deflection of crt trace Remove the core from the secondary tuned circuit of the discriminator or ratio detector and adjust all cores for maximum deflection of the crt trace Since the shape of the response will vary with the design of the IF stages some curves will not appear as shown in Fig 5 but will have sharp peaks In the latter case an additional check can be made if a tuning indicator is fitted as this will generally show maximum deflection when the cores are correctly adjusted The final curve should in all cases be symmetrical about the vertical graticule and in some cases the service manual will illustrate the type of curve which sh
48. ree ranges 85 90 90 95 and 95 100 5 Each of the outputs is controllable in amplitude by the RF OUTPUT control R22 which varies the anode voltage of the mixer valve V2b The additional tuned circuit L10 C79 ensures that enough of the 20 mc s signal is available at the mixer grid AIRMEC RADIVET MODEL 211 26 37 The output signal passes via C17 54 which imposes 20 db attenuation in two of its settings to the output Step Attenuator housed at the end of RF OUTPUT lead Probe A It is possible to pass an audio frequency or 50 c s signal via the AM switch 52 to the screen of the crystal harmonic amplifier V3a This will result in amplitude modulation to a constant modulation depth of the output on all ranges Freguency modulation at an audio freguency or 50 c s can be passed to the DEVIATION control via the FM switch S1 C6 and R8 form a pre emphasis network so that the audio signals may be pre emphasised to the same degree as the BBC transmissions This means a maximum deviation of 14 kc s at 40 c s rising to a maximum of 75 kc s at 15 kc s modulating frequency De emphasis should take place in the receiver 8 3 Audio Oscillator Triode valve V3b operates as an audio oscillator feedback from anode to grid being applied by the phase reversing auto transformer T1 Freguency selection is by means of the switch S5a which determines which of 11 Wien bridge networks is in use The amplitude of oscilla
49. s R F stages receivers Alignment Check on spot I freguencies receivers LF response receivers Discriminator response receivers Locating faults I F stages F M receivers Overall response receivers Locating faults RF stages F M receivers Alignment check on spot frequencies receivers rejection receivers Discriminator Limiting action receivers Check on de emphasis circuits receiver Check on phase distortion AF stages Check on harmonic distortion AF stages Overall response stages Locating faults A F stages Overall response Loudspeakers Qutput meter A C Valve Voltmeter D C Valve Voltmeter General Purpose Oscilloscope FACILITIES USED F M signal generator and oscilloscope A M signal generator and oscilloscope A M signal generator and oscilloscope A M signal generator and oscilloscope C W amp A M signal generators and oscilloscope signal generator and oscilloscope F M signal generator and oscilloscope signal generator and oscilloscope signal generator and oscilloscope F M signal generator and oscilloscope C W amp F M signal generators and oscilloscope F M amp A M signal generators and oscilloscope F M amp signal generators and oscilloscope F M Signal generators with Pre emphasis and 7 oscilloscope Audio oscillator and oscilloscope Audio oscillator and oscilloscope
50. s may be applied to frequencies above 2 kc s 6 2 1 Recording level Bias Frequency Loops AUDIO OSC Frequency 40 5 8 42 2x7 12 44 2 x 11 8 45 3 15 48 4 12 50 10 5 52 2 x 13 8 54 2x9 12 56 7 8 60 4 15 Using the above connections record short lengths of tape at different record inputs checking that the crt display shows no signs of distortion i e the record amplifier is not being overloaded and tabulate the levels used against footage indicator readings The maximum input that should be used is just below the level that overloads the record amplifier When this has been completed disconnect Probe B connect Probe C to some suitable point in the playback amplifier chain and play back the tape Tape saturation will cause distortion of the waveform displayed on the oscilloscope and the correct record level can thus be identified 6 2 2 Record characteristics When making this check the tape may if desired be removed from a machine that is not fitted with an automatic stop Connect the RadiVet as tabled in Sect 7 2 1 and adjust the AUDIO OUTPUT and record level controls until the correct level is indicated Set the AUDIO OSC at 40 c s and measure the amplitude of the deflection of the crt trace Repeat this at all frequencies from 40 c s to 15 kc s and plot the results to illustrate the record characteristics AIRMEC RADIVET MODEL 211 23 37 6 3 Over
51. sion should arise regarding the shape of the response curve Bandwidth measurements may be made in the manner outlined in Fig 5 but the value obtained will generally be of the order of 5 to 10 kc s instead of 200 kc s as guoted in the example 4 2 RF Alignment Check The freguency accuracy of the RadiVet after crystal calibration is high enough for the RF alignment of AM receivers on the short wave bands to be carried out At the lower freguencies however that is in the medium and long wavebands the RadiVet scale must be checked as indicated in Sect 5 AIRMEC RADIVET MODEL 211 19 37 RadiVet is then connected as tabulated in 4 1 2 and the RF circuits aligned as described in the manufacturer s instructions An alternative method for calibrating the RadiVet at low freguencies is given below This is very simple but only provides a series of accurate spot frequencies Set the RadiVet to 1 25 mc s as checked by the crystal calibrator and connect as follows Probe or Switch Connection or Setting Probe RF Aerial input Probe B Audio Not used Probe Oscilloscope Across loudspeaker terminals FM OFF AM VAR FREO AUDIO OSC Any suitable frequency say 1 kc s GAIN AC position as reguired to give a display of reasonable amplitude without overloading the Y amp X PLATES 50 c s or any ofthe first 4 TB positions TUNING 1 25 mc s RANGE 0 5 5 OUTPUT Maximum
52. st gear for completely checking aligning and locating faults in all stages of both FM and AM broadcast receivers Basically it consists of three guite independent instruments housed in one case an AM FM Signal Generator with Crystal Calibration an Audio Oscillator and an Oscilloscope These three instruments which can be used either separately or interconnected by means of switches on the front panel enable every function of a receiver to be thoroughly investigated The exceptionally robust construction of the instrument coupled with the very high quality of workmanship employed in its manufacture ensure a long trouble free life All controls are recessed for maximum protection and the probe leads which are normally stowed in the end compart ments are permanently attached to avoid acciden tal loss The chassis is isolated from the case and earth so that AC DC sets can be tssted ss easily as AC sets R F SIGNAL GENERATOR The radio frequency signal generator incorporated pro vides signals from 0 15 Mc s and 65 100 Mc s in 4 ranges cach range having a constant width of 5 Mc s It is thus usable over ali the AM and FM broadcast bands and their respective IF bands Step and variable attenuators enable the output to be varied continuously from about 5 micro volts up to about 59 millivolts TUNING DIAL A feature of the Generator exclusive to Airmec is e linear tuning dial system see Figure 1 which enables very high
53. t 50 c s a discriminator response obtained on the Oscillotcope Amplitude Modulation is then applied the degree of miting is immediately shown on the trace as illustrated in Figures 4b and lt Figure 4 Wobbulator display of a discriminater characteristic bolanccd for maximum Amplitude Modulation rejection When applied to frequency modulate the R F Signal Generator the normally constant amplitude output af the Audio Oscillator may be modified to provide pre emphasis identical to that employed by the 0 6 C This is obteined timpiy by switching from Normal to Pre emphasis From the summary of feacures given shove it will be seen thet the Audio Oscillator is extremely versatile and can be employed for a wide range of tests The con stane output level enables the frequency response of atl audio amplifiers including types to be rapidly checked By using the Oscillcsccpe 31 an cutput meter and at the same time with the Audio Osc tlater sgail applied to the X places as a time base both the phase snd harmonic distortion of the Audio amplifier can be checked ac shown in Figures Sa b and Simitarty the frequency fesponie and phase and her monic distortion characteristics of a complete AM receiver Figure 4 hb Wobbulator display of disceiminator or any of it can be checked by using the Audio characteristic when limiter is not operating correctly Oscillator to Amplitude
54. ter facility and may then be adjusted as required If the correct bias amplitude is unknown it may be ascertained as follows AIRMEC RADIVET MODEL 211 22 37 Connect Probe B to the record input terminals set the AUDIO OSC to 400 c s adjust the AUDIO OUTPUT and record level controls to the normal recording level and measure the Bias Amplitude by means of the AC Valve Voltmeter facility Record short lengths of tape at different bias levels and tabulate bias levels against footage indicated readings Play back the recorded lengths using the AC Valve Voltmeter facility to measure the output from each length of tape and tabulate the results of output against footage indicator readings If these two sets of results are combined to plot the curve of output amplitude with reference to bias level the correct bias level can be determined from the curve as illustrated in Fig 6 6 2 Recording The correct recording level which is normally taken as being half the signal input necessary for tape saturation is important if the optimum signal noise ratio is to be obtained whilst still permitting the recording of reasonable peaks without distortion If true reproduction is to be obtained using a playback amplifier having the accepted increase per octave below 1 kc s the record characteristics must be correct It is normally level up to the anode of the final amplifier though in some cases pre emphasi
55. the probe flying lead into the divide by 10 or divide by 100 sockets or by a further factor of 10 by turning the OUTPUT switch to the appropriate 20 db position With any of these output conditions continuous decrease of output level by a further 10 times 20db may be obtained using the OUTPUT control For the signal to be un modulated the FM and AM switches should be set to OFF 2 3 2 Amplitude Modulation With the signal generator set up as indicated in Section 3 3 1 above amplitude modulation at a fixed depth of approximately 30 may be applied by turning the AM switch either to 50 c s or VAR FREQ as required If turned to VAR FREQ the modulating frequency will be that selected by the AUDIO OSC FREQ switch 2 3 3 Frequency Modulation Normal FM with a maximum deviation of 75 kc s may be obtained by setting the controls as indicated in Section 3 3 above but with the FM switch at VAR FREQ NORMAL The AM switch should be set to OFF The modulating frequency is the audio frequency selected by the AUDIO OSC FREQ switch Deviation is approximately 75 kc s with the DEVIATION control at maximum clockwise and may be decreased by turning this control in an anti clockwise direction An FM signal having the correct BBC pre emphasis characteristic of 50 microseconds may be obtained with the FM switch in the VAR FREQ PRE EMPHASIS position With DEVIATION control at maximum the deviation is then approximately 75 kc s with a 15 kc s modula
56. ting frequency and 14 kc s at 40 c s High deviation at 50 c s may be obtained when using the instrument as a wobbulator but this facility is dealt with in Section 3 5 2 3 4 Simultaneous FM and FM at 50 c s and AM at a variable frequency or vice versa may be obtained by placing the FM and AM switches in the appropriate positions The former is required for checking the AM rejection of ratio detectors which is dealt with in Section 4 3 2 4 Audio Oscillator The output of the audio oscillator may be obtained from Probe B when the OUTPUT control is at any position other than XTAL CHECK The audio frequency will be determined by the setting of the AUDIO OSC FREQ switch The output voltage with the AUDIO OUTPUT control in the maximum clockwise position is approximately 0 7 volts RMS 2 volts peak to peak and may be reduced by rotating the AUDIO OUTPUT control in an anticlockwise direction The actual output voltage may be monitored and measured by turning the Y GAIN control to the INT CHECK position when the waveform of the output signal may be observed and the voltage measured by the method described in Section 3 8 1 Note that the waveform will disappear if the Probe B leads are short circuited AIRMEC RADIVET MODEL 211 12 37 2 5 Wobbulator Operation as a wobbulator involves sweeping the HF oscillator that is applying FM at a relatively low frequency and high deviation and applying this s
57. tion is limited by the power sensitive thermistor R36 which loads the circuit in such a way that the output at each freguency is limited to the same value and is undistorted by the valve Apart from providing outputs for FM and AM the circuit also provides an output for the X scan of the crt and one at Probe B which is controllable by means of R55 AUDIO OUTPUT 8 4 Oscilloscope The cathode ray tube V6 is employed in a conventional circuit with R78 and R 75 as the BRILLIANCE and FOCUS controls respectively The Y Amplifier valve V4a is a pentode DC coupled to the Y2 plate of the crt to provide the correct voltage sense on the screen A variable negative bias voltage is applied to the grid circuit at the bottom end of the input potentiometer S6 GAIN This voltage is derived from the current through the crt supply chain and its value may be set by means of the pre set control R80 which is used to calibrate the Y SHIFT VOLTS control R60 The combination of the calibrated input attenuator and Y SHIFT control enables measurement to be made of AC or DC input voltages applied to Probe C When the input attenuator S6 GAIN is set to INT CHECK the output from the audio oscillator is fed out to Probe B and also to the Y amplifier so that the level may be monitored by means of the AC voltage measurement facility A small proportion of the anode signal voltage developed across R63 is fed via C47 to obtain synchronisation in the T
58. used in conjunction with the Oscilloscope to give a wobbulator display of the 1F response of F M and A M receivers and the Dis triminator response of receivers see figures 2 and 4a The frequency of any point on the response curves can be immediately identified by setting it under the cur sor line on the CRT screen by means of the tuning can trol and reading the frequency directly off the tuning dial Similarly the bandwidth of a response curve either LF or discriminator can be ascertained directly by moving it across the screen and noting the figures a which the leading and trailing edges fall under the centre cursor LE WAVEFORM WITH 6 OB POSITION OF LEADING EDGE UNDER CURSOR EA ON lt B IE WAVEFORM OF A MOVED TO PLACE 6 08 POSITION OF TRAILING EDGE UNDER CURSOR BANDWIDTH BETWEEN 6 08 LIMITS IN THIS EXAMPLE IS 10 6 10 8 Me s line In the cate of 1 F response curves if the amplitude is correctly adjusted to fill the space between the O and Infinity marks on the screen the bandwidth between any particular levels on the curve may be determined as illus trated in Figure 3 Figure 2 Typical I F response curve of a Frequency Modulated receiver Complete alignment of an F M receiver can therefore be carried out without the need for guesswork and in 3 fraction of the time taken by any other method FREQ 10 6 Mc s gt SAY FREQ 10 8 Mc s SAY
59. ut is in each case obtained by mixing the outputs of two oscillators one of which may be freguency modulated and the other amplitude modulated The signal may therefore be un modulated modulated with FM or AM or simultaneously with FM and AM at different modulating freguencies In addition signals in the bands 0 30 mc s 45 60 mc s 65 80 mc s and 195 240 mc s obtainable at a lower output level see Sect 8 The signal generator output is fed through a coaxial cable to a probe unit which contains an attenuator Output signal levels between approximately 5 micro volts and 50 milli volts may be obtained 1 1 Wobbulator The signal generator may be freguency modulated at 50 c s with a freguency sweep of up to 500 kc s If this signal is applied to the IF section of an FM receiver and the resultant audio signal is applied to the Y plates of the crt in the RadiVet a wobbulator display of either the IF filter characteristics or the discriminator or ratio detector characteristics may be obtained The effect of trimming these circuits can be observed and the circuits aligned for optimum performance very rapidly If a ratio detector is being aligned since it is possible to provide simultaneous AM at a higher frequency the wobbulator display so obtained enables the circuit to be set up correctly for optimum rejection of AM A similar procedure using a very much lower frequency sweep can be applied to give the response characteristics o
60. ve ranges 70 75 mc s and 75 80 mc s The main tuning capacitor is C7 and this has been made linear in frequency by an adjustable capacitor C8 which is set up at each megacycle calibration point in the factory Each calibration adjustment is accessible in turn through the plugged hole in the front panel as the dial is rotated Re adjustment should not be attempted without the correct equipment In order to be able to adjust the oscillator against the crystal calibration a trimmer C75 which is accessible at the right hand side of the case has been provided A proportion of the common anode signal voltage of the valve V1 is fed via the quadrature network formed by the anode to grid capacitance of Vla and R1 to the grid of Vla Vla signal current is then in quadrature with the current of V1b Both these currents pass into the common tuned circuit and the frequency is dependant on the proportion of these currents The amount of quadrature current is controlled by altering the bias of Vla by means of signals fed to the grid via the DEVIATION control R4 This results in frequency modulation of the variable frequency oscillator The signal is then fed to the pentode buffer amplifier V2a This amplifier is flatly tuned over the range 65 80 mc s and shares a common anode circuit with the crystal harmonic amplifier V3a The oscillator valve V5b is a pentode which generates the fundamental crystal frequency of 5 mc s by using the screen as the anod
61. vers It is therefore recommended that an early opportunity be taken to check the scale accuracy at low frequencies This should be done by calibrating the instrument at 0 and 1 25 mc s with the Crystal Calibrator as outlined in Sect 3 2 and comparing the output frequencies with the tuning scale readings of a receiver of known accuracy If the more common calibration frequencies are checked and the corrected scale readings noted these frequencies can always be reproduced with a very high degree of accuracy The crystal calibration must be accurately carried out each time these low frequencies are required 4 1 1F Response Connect the RadiVet as tabulated in Sect 4 1 1 and align all IF cores and trimmer capacitors for maximum output If it is desired to obtain a wobbulator display of the IF response connect the RadiVet as in Sect 4 1 2 set the DEVIATION control initially to about 1 5th of its total clockwise movement and adjust as required A trace similar to that shown in Fig 5 will probably be obtained but reference should be made to the service data sheets to find the correct response A much smoother control of deviation can be obtained if the X plates are switched to VAR OSC the FM switch is set at VAR OSC NORMAL and the AUDIO OSC set to a frequency between 40 and 400 c s Under these conditions some receivers may present a double trace because of phasing differences and the absence of blackout on the trace return but no confu
62. vice Engineer has a tool which will tell him less than a minute how well a receiver is performing over its entire audio frequency range The versatile Y amplifier has a sensitivity of approxi mately 0 7 volts cni and a frequency response from D C to Mc s The input attenuator and Y shift are cali brated in both RMS values for measuring A C voltages and neak values for measuring pulse waveforms and D C Input voltages are applied via a special probe which has an input impedance of 10 megohms en connections and megohm when switched to A C connections Thus the Oscilloscope can not only be used for examining all types of waveforms but is invaluable as a high imped ance and D C valve voltmeter Typical voltages which cannot normally be measured correctly by moving coil meters are for example those appearing on valve grids due to oscillation or leaky coupling capacitor those appearing on valve electrodes fed from high value resistors particulariy in battery sets where the valve cur rents are email and those appearing on AVC lines etc A C measurements from to 230V RMS and D C measurements from 1 0V xo 2000 can be made USES OF THE RADIVET The following is a brief list of some of the possible applications of the RadiVet showing the facilities employed TEST PERFORMED ON LF response receivers Locating faults LF stages A M receivers Overall response A M receivers Locating fault
63. voltages at a frequency of 50 c s and having no superimposed DC may be measured with the Y GAIN control in the DC positions The general procedure is the same as for 3 8 1 and the voltage ranges are 0 7v RMS DCx 10 0 20 DCx 30 0 70v DCx 100 0 400 j DCx 300 0 1400v i DC x 1000 3 TESTS ON FM RECEIVERS 3 1 1 F Response Service manuals may call for either the single spot frequency or wobbulator method of alignment but whichever method is used it must be remembered that most modern FM receivers incorporate a limiter The signal input level should be kept as low as possible and must always be less than the minimum necessary to operate the limiter Even if a high level limiter such as is employed with a ratio detector is encountered the same warning still applies 3 1 1 Spot Frequency Alignment Probe or Control Connecting or setting Probe A RF Signal grid of frequency changer Probe B Audio Not used Probe C Oscilloscope Live side of volume control see text FM OFF AM VAR FREQ AUDIO OSC Any suitable frequency say 1 kc s GAIN AC x1 PLATES 50 c s or any of the 4 TB positions TUNING Receiver intermediate frequency RF FREQ RANGE as required OUTPUT Minimum possible consistent with reasonable deflection of the crt trace Some types of receiver use an IF which is higher than 15 mc s Since the output of the RadiVet is obtained by mixing the output from a variable frequency oscillat

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