MFJ-8100 World Band Receiver
Contents
1. Test your headphones on a personal stereo and compare them to one or more other headphones It is very possible for inexpensive headphones to become defective Also make sure that the battery is in good condition Steady high pitched squeal or whistle Regeneration control is turned too far clockwise NOTE We have designed this book and the receiver itself to assure that you can install it easily and enjoy If after installing your receiver double checking steps and going over the preceding trouble shooting suggestions you are still having a problem please contact MFJ s Technical Help Department at 1 800 647 TECH Before calling please be prepared to explain your exact difficulty as exactly as possible NOTES FOR HAM OPERATORS amp EXPERIMENTERS This receiver has a single intended purpose to help newcomers young and old alike to enjoy tuning the sheer magic of shortwave radio You ll quickly gain the skill of finessing the regeneration control to choose AM shortwave broadcasts SSB or CW RTTY The MFJ 8100 just might be the very best regenerative receiver ever designed but it is not intended to be all things to all people The MFJ 8100 s PC board is a very roomy platform which may SEEM to invite countless modifications However please remember the original purpose of th receiver befor hacking It s a beginner s first shortwave receiver desig2. Maximum gain is clockwise when viewing the rear panel A good normal setting is 3 4 of its full rotation If you are using a marginal antenna 5 to 10 feet of wire indoors keep R9 at its maximum setting If you are using a very good antenna a long high outdoor wire or ham antenna keep RO at about 2 3 or so of its range If your listening interests require frequent RF gain adjustments install an external 10K control in series with your antenna MF J 8100 World Band Receiver REGENERATION RANGE TRIMMER R20 Ordinarily this trimmer is adjusted only after kit construction or in the unlikely event that any of the FET transistors are replaced This adjustment assures smooth regeneration over all five of the tuning ranges See Construction Phase 5 DIAL CALIBRATION TRIMMER C5 This one time internal adjustment is made with a miniature screwdriver in order to assure that the frequency markings on the front panel are as accurate as reasonably possible EARPHONE JACKS J2 J73 These two jacks accept 1 8 3 5 mm STEREO plugs as used in Walkman type headphones or mini speaker systems The audio output is monaural the two jacks are wired in parallel to permit the use of two headphones NOTE if a mono 1 8 plug is used for any reason it must not be pushed all the way in or it will short out the audio ANTENNA CONNECTOR
3. 1990 s A fair question but the MFJ 8100 is not like any regenerative HF receiver you v ver used before Our GOAL determined the design and circuitry of this receiver We wanted the following features GOOD reception of BOTH shortwave AM and CW SSB Ease of kit construction for newcomers Reasonable price A quality look and feel Relatively simple circuit No critical alignment requirements Low parts count yet not dependent on specialty IC s Purposeful choice of tuning ranges for SWLing anytime Satisfactory AM CW SSB listening and circuit simplicity were our primary goals Despit th popularity of NE602 type direct conversion circuits among today s experimenters and some kit vendors direct conversion is NOT satisfactory for ENJOYABLE listening to AM shortwave broadcasts Merely nulling the carrier does not result in true listenability Similarly a multi band superhet with BFO could not fit our goals of simplicity and economy To meet our goals we chose to refin th regenerative concept as much as possible using contemporary design concepts and component characteristics Our first goal was to tame the regeneration process itself to minimize the instability and unwanted oscillations so typical of traditional regenerative circuits and so that even a beginner can enjoy and understand the use of the Regeneration Control The result of our re design is an HF SWL receiver with bette
4. CW pitch for the most pleasing sound or best clarity in a SSB voice signal After you ve had some practice with using the regeneration control it will become second nature giving you a sense of real control over the performance of your receiver TUNING SSB Single Sideband VOICE SIGNALS SSB signals are all those voice signals which sound like Donald Duck unless they are tuned in very exactly They have no background carrier as do AM broadcast signals 11 MF J 8100 World Band Receiver On modern ham radio transceivers tuning SSB is made so easy by means of internal filters that many licensed ham operators are not aware of the basic technique for tuning in SSB signals on receivers without such filters The first fact to know about any given group of SSB signals is whether they are Upper USB or Lower LSB Sideband In ham radio communication LSB is used on 1 8 through 7 3 MHz and USB is used for all higher frequency bands 14 18 21 28 MHz The best band to practice SSB tuning with your receiver is the 75 Meter band 3 8 to 4 0 MHz doing so in the evening when the signals are strong and plentiful Notice that the band is spread out on the dial more than are the other amateur bands which permits easier tuning These are all LSB lower sideband signals Think to yourself for LOWER sideband tune DOWN for UPPER sideband tune UP In practice this means that yo
5. J1 This binding post permits easy hookup of any wire or a banana plug may be inserted in its end 10 to 20 feet of ordinary hookup wire also called bell wire provides good basic reception even when installed indoors See the section on Antennas in this book for more information GROUND CONNECTION For casual operation a ground connection is optional However a wire from this connector to a ground rod or cold water pipe will reduce unwanted noise and interference from nearby electrical devices or AC wiring and may boost receiver sensitivity Attach the wire between the two washers then tighten the wing nut UNDERSTANDING amp USING THE REGENERATION CONTROL In theory your receiver s Regeneration Control adjusts the level of feedback or self oscillation of the FET detector section Q1 and Q2 In PRACTICE this control is like a Joystick for managing and optimizing receiver performance Your ability to handle this joystick saves you many dollars over today s cost of receivers which perform similar functions automatically In fact you might even get more control over receiver performance in varying situations than may be possible with more elaborate receivers 10 MF J 8100 World Band Receiver With the control turned fully to the left counter clockwise the receiver is virtually silent Regeneration begins at a certain point as you turn the control cloc
6. metal roof In fact radio hams and serious SWL s have xperimented with thousands of imaginative antenna ideas VERY IMPORTANT Use care and common sense when putting up outdoor antennas Be certain that your wires or your ladder cannot come into contact with electrical power lines You can be KILLED by accidental contact with power lines YOUR RECEIVER S AUDIO CIRCUIT MANY WAYS TO LISTEN IN The LM386 audio amplifier IC circuit is designed to provide ample volume to not one but TWO headphone jacks We used stereo jacks because today s economical personal music headphones are as inexpensive as were the bulky basic headphones of yesteryear Your receiver provides two headphone jacks to make it very easy for two people to listen together 14 MF J 8100 World Band Receiver The amplifier circuit provides sufficient output for moderate speaker volume Miniature speaker systems designed for Walkman and similar personal stereo devices will plug right into J2 or J3 and work very well However please remember that the amplifier is specifically designed for headphone operation If you prefer room level speaker volume for long listening sessions we recommend an external amplifier as discussed below If you use personal FM cassette or CD players you probably also know all about those compact amplified speakers designed specifically to plug into the stereo jack of compact
7. one vacuum tube half of the tube served as a regenerative receiver and the other half was a low power crystal controlled transmitter In addition many thousands of engineering careers as well as ham radio licenses wer launched with the building of my first shortwave radio from do it yourself regenerative MF J 8100 World Band Receiver receiver kits offered by the major radio companies of several decades ago The fondest dream BACK THEN of most of these radio builders was to be able to afford to move up to a superhet communications receiver Their fondest memory TODAY is that very first receiver kit From the late 1970 s through the 80 s as consumer electronics and new ham radio equipment became more sophisticated so very rapidly interest declined not only in regenerative receivers but also in kit building and even in shortwave radio listening One or two generations of Americans simply missed out on the thrill and satisfaction of building AND UNDERSTANDING a simple radio set which could receive signals from anywhere in the world Back to Today and the Future Your MFJ 8100 is a much better receiver than the classic radio sets which attracted several generations of Americans to th xCcitement of radio and electronics In fact its basic performance is superior to many of the simplest superhet receivers which were considered such a great step beyond
8. personal stereos Thes speaker setups have a built in amplifier circuit and their own separate batteries Any of thes devices should work well with your receiver Radio Shack carries a variety of amplified speaker pairs as well as several monaural utility amplifiers Even though stereo jacks are used remember that the receiver audio output is monaural An external amplifier can also be a rewarding do it yourself construction project One half to 2 watts will provide generous and ample speaker volume In fact if building this receiver has kindled your interest in building something on your own you could get started by duplicating the same LM386 audio circuit used in this receiver Use th same parts values and physical positioning as we did The volume control may be omitted since you already can control the receiver s volume The amplifier will operate on 6 to 15 volts DC All needed parts are available at Radio Shack stores You ll get plenty of volume for any size of utility or communications speaker AUTHOR S NOTE I have fully tested this use of a second identical LM386 IC circuit with speaker and can recommend it highly to all who can t confine all this listening excitement to one or two headsets VERY IMPORTANT A monaural 1 8 plug will fit the receiver s stereo jacks HOWEVER the plug must NOT be pushed all the way into the jack because it will short out the audi
9. MF J 8100 World Band Receiver MFJ 8100 World Band Receiver Table of Contents For Beginners Page 2 Just a Bit of History Page 2 Back to Today and the Future Page 3 A Simplified Explanation of How it Works Page 3 For Experienced Hams Enthusiasts and Engineers Page 4 Receiver Controls and Connections Page 6 Understanding and Using the Regeneration Control Page 7 Tuning SSB Voice Signals Page 8 Using and Enjoying Your Receiver Page 9 Setting Up A Useful Shortwave Antenna Page 9 Your Receiver Audio Circuit Page 10 About the 5 Tuning Ranges of Your Receiver Page 11 Shortwave Listening in General Page 12 In Case of Difficulty Page 12 Notes for Radio Hams amp Experimenters Page 13 Conclusion Page 14 Some Helpful Terms amp Abbreviations Page 15 Sample SWL Log Page Page 17 MFJ 8100 Parts List Page 18 PC Board View Page 19 Schematic Diagram of MFJ 8100 Receiver Page 20 MF J 8100 World Band Receiver Instruction Manual written by Dan F Onley K4ZRA Copyright 1993 by MFJ Enterprises Inc All Rights Reserved MF J 8100 World Band Receiver For Beginners You re about enjoy a versatile shortwave receiver which employs a circuit concept that is as classic as the 1920 s but which uses modern engineering that takes advantage of the advanced capabilities of today s electronic components This shortwave radio is designed to let you listen to a great var
10. aining an acid or salt paste electrolyte and is generally polarized with a positive and negative side Correct polarity MUST be observed when installing electrolytic capacitors FET Field Effect Transistor Ground Refers to all points and surfaces in an electronic device which are connected to the DC side of the power supply or battery A ground plane of a Circuit board is the large area of copper plating that is common to ground Barth ground refers to water pipes or metal grounding rods in direct contact with Mother Earth EC Integrated Circuit A tiny plastic rectangular block with 6 8 14 or more pins containing a Silicon chip which provides the equivalent of dozens or hundreds of individual transistors and resistors K abbreviation for 1000 ohms 10K 10 000 ohms KHz KiloHertz MHz MegaHertz Inductor A coil or loop of wire used in electronic circuits Oscillator s Regeneration pF picofarad a tiny unit of capacitance megohm one million ohms Regeneration Regenerative a method of boosting the performance of a simple detector by feeding the detected signal back to the input of the detector for further amplifying This oscillation process must be controlled carefully through the use of a regeneration control RF Radio Frequency Energy in contrast to audio or DC RELF Radio Teletype SSB Single Sideband a method of voice transmissi
11. ating detector to behave as an unstable but potent QRP transmitter R4 reduces the Q of L1 10 uH for smoother regeneration The SW1 bandswitch selects a combination of simple inductors For example the total inductance for Band A is L1 L2 L3 L4 L5 The inductance for Band E is only L5 And so forth Air variable Cl uses its 50 pF range and mechanical vernier reduction to provide smooth bandspread in parallel with C3 and trimmer C5 which perform the traditional bandset function Trimmer pot R20 ensures adjustability for smooth regeneration over all tuning ranges regardless of individual FET characteristics C17 C9 C10 and R9 form a low pass filter to block RF from the audio amplifier and provide basic audio filtering Volume Control R2 varies OUTPUT rather than low level input to the LM386 audio amplifier This approach further isolates the RF stages from variations in the audio section The LM386 IC1 circuitry employs all recommended options for maximum gain and protection from self oscillation MF J 8100 World Band Receiver To prolong useful battery life the LED CR1 indicator R13 limits current draw by to minimum reasonable visibility as an on off MF J 8100 World Band Receiver RECEIVER CONTROLS AND CONNECTIONS Most of the controls are self explanatory However it is very important to understand the correct use of the R
12. egeneration Control and the two internal trimmer adjustments of the receiver BANDSWITCH SW1 This quality rotary switch selects any one of the 5 tuning ranges from A to E indicated on the tuning scale TUNING C1 The Tuning knob controls an air variable capacitor Cl which also has a built in 6 1 vernier reduction drive to which the dial pointer is attached This reduction permits very smooth tuning The frequency markings on the dial scale must be understood to be approximate due to the 10 tolerance ratings of the fixed inductors L1 through L5 PUSH SWITCH SW2 AND L E D INDICATOR CR1 While the purpose of the on off switch and LED is obvious remember to turn your receiver OFF when not in use A weakened battery degrades receiver performance REGENERATION R1 Because understanding and controlling regeneration is at the heart of your receiver s performance we ve provided a separate section on its use In brief it controls receiver sensitivity and adjusts between AM broadcasts and CW SSB VOLUME R2 This potentiometer performs the normal function of any volume control Of interest to the technically minded it controls the output of the LM386 audio IC rather than the input which enhances the stability of the regenerative detector RF GAIN R This trimmer potentiometer is adjustable with a small screwdriver
13. iety of international broadcasts You can choose from five different frequency bands so that you can count on hearing SOMETHING at any hour of day or night Also this receiver lets you hear a generous sampling of ham radio signals both Morse code CW and voice SSBE communications plus many other government and commercial transmissions Just a Bit of History The regenerative receiver moved the world of radio reception and broadcasting beyond the limits of crystal sets useful only for hearing a strong local signal For over a decade thes magical whistling squawking glowing boxes were the norm for home listening as well as for the first generation of radio hams Receiver design evolved swiftly The superheterodyne became the norm during the 1930 s Regenerative receivers often called Gennies were left to tinkerers and beginners Even though these receivers were simple and quite sensitive they had a number of shortcomings instability touchiness difficulty in separating strong stations a tendency to generate interference to other receivers and a general reputation for making odd sounds that resembled everything from pigs to motorboats However the sheer SIMPLENESS of the regenerative circuit remained attractive to experimenters and beginners In fact as recently as the 1960 s one company marketed a 14 kit for building a complete transceiver using only
14. kwise The exact point varies not only from band to band but even as you tune within a given band Regeneration begins as an audible increase in background noise followed by a soft hiss The hiss or any signals that may be on frequency increases as you continue to turn clockwise If you go too far the signal becomes distorted or the receiver begins to squeal oscillate Always use the LEAST amount of regeneration necessary for good reception of a given signal As a rule the best reception of AM shortwave broadcast signals occurs just BEFORE full regeneration If you hear a whistle carrier along with an AM signal turn the control back slightly until the carrier disappears When there are a number of very strong shortwave AM broadcasts in a given band such as iS common in the early evening you will find it possible to tune them in one after the other with the regeneration control set way back and requiring virtually no adjustment In other words you would tune from station to station just as if using any other type of shortwave set When the receiver is adjusted for good AM reception CW signals will sound like hisses Advancing the regeneration control slightly will bring in the familiar beeping associated with CW RTTY radio teletype or similar signals The regeneration control can also serve as a fine tuning control permitting slight adjustments of
15. make it very easy for you to listen to ham radio stations at night on what is known as the 80 75 Meter band From 3 5 to 3 8 MHz you ll hear mostly Morse Code signals From 3 8 to 4 0 MHz you will hear SSB voice conversations from all around the nation You ll hear both sides of most conversations You may hear occasional shortwave broadcasts mixed in among the hams in the 3 9 to 4 0 MHz region and possibly in the 90 Meter band 3 2 to 3 4 MHz Range B 5 85 to 7 40 MHz The main purpose of this tuning range is to give you lots of strong shortwave broadcasts in late afternoon and throughout the night on the 49 meter band 5 95 to 6 2 MHz The 40 meter ham radio band is 7 0 to 7 3 MHz and you will also hear foreign broadcasts among the ham CW and SSB signals Range C 9 5 to 12 00 MHz This band lets you tune all of the popular 31 meter broadcast band 9 5 to 9 9 MHz You can also find the WWV time standard signal at 10 0 MHz or on Band D at 15 0 MHz The 16 MF J 8100 World Band Receiver 30 meter ham band CW and RTTY only in the USA is at 10 1 to 10 15 MHz This tuning range is generally busy 24 hours a day Range D 13 2 to 16 4 MHz On the 20 Meter ham band 14 0 to 14 35 MHz you can hear strong CW and SSB voice signals from around the world throughout the day and well into the evening This is the most active and crowded of the international ham radio bands You also are able to tune the 21 Meter shortwa
16. ned for the most popular SWL broadcasts plus a SAMPLING of our ham bands If you expect to pass it on as a gift or resell it it would be prudent to accomplish any desired modifications on the outside of the receiver itself For example the function of the RF gain control can be duplicated with a pot at the antenna connector with no drilling required Similarly alternative DC power additional audio amplification or audio filtering can be provided externally If you change any values in the L C tuning in order to try a band of special interest be sure to note such changes in this manual Remember that changing C3 or any inductance affects the tuning range of ALL the bands 18 MF J 8100 World Band Receiver Author s Hint To save you time as well as wear and tear on the PC board here s what my own curiosity showed reducing C3 can easily bring in 12 and 10 Meters on Band E However attempts to increase this capacitance beyond 220 pF without ALSO increasing total inductance are pointless if you re looking for good 160 Meter performance While it s not intended as a communications receiver the very fact that the MFJ 8100 covers all or part of so many different popular CW bands might intrigue some QRP enthusiasts interested in multi band portable trans receiving The author conducted a few simple tests using an HW 9 for transmitting side by side with the 8100 on 30 20 17 and 15 meters You will wa
17. nt T R switching to short the receiver antenna input to ground and also to mute the audio Plan on a separate keying sidetone Frequency spotting must be done with a very low RF level Receiver stability when switching the antenna input is amazingly good even at 21 MHz While the 8100 is not represented as a communications receiver you indeed can have some multi band QRP fun with it And FUN is exactly what this great new receiver is all about Look at it this way If you take your multi band QRP mini transmitter and MFJ 8100 on a trip and happen not to work DX or anybody else you can still dial up BBC VOA Moscow and many more places of our ever shrinking global community CONCLUSION If you really enjoy shortwave radio listening you ll probably yearn for and eventually get a more elaborate receiver You might even work on getting a ham radio license and setting up a station for transmitting and receiving As the years go by we have a hunch that you ll always remember the first thrills of listening to your MFJ 8100 And because it s rugged compact and far more sophisticated than the first receivers of yesteryear we suspect you ll actually 19 MF J 8100 World Band Receiver keep it and keep on listening to it when nobody else is looking LEARNING MORE The purpose of your Receiver and the details provided in this instruction manual are to help you become better acq
18. o output If you have reason to use a mono plug insert it just far enough for the tip to make firm contact with the first section inside the jack ABOUT THE 5 TUNING RANGES OF YOUR RECEIVER 15 MF J 8100 World Band Receiver The purpose of the following information is to give newcomers a general idea of what to expect to hear in each of the 5 frequency ranges tuned by your receiver First please understand that the frequency markings on the tuning dial can be only approximate They indicate the general neighborhood of major frequency bands and have an accuracy only within a few hundred KHz If you are wondering what it would take to make the dial perfectly accurate imagine an adjustable trimmer capacitor AND an adjustable coil for EACH band The process of making these many adjustments is called alignment and also requires th use of frequency measuring equipment far more costly than the receiver Whenever you hear a broadcast of special interest to you which you would like to be able to find again make a note of the time frequency band and approximate dial position In fact such notes are called a Shortwave Listening Log A sample log page is printed in this book which you may copy to make your own logbook Or use your computer to design the style of logging pages best for you Range A 3 5 to 4 3 MHz The primary purpose of this tuning range is to
19. of satisfying listening provided that you turn th receiver OFF when not in use This advice may see ridiculously obvious but remember that battery replacemen The better the antenna the better the reception general 20 to 30 feet of wire will give good results In The use of the Regeneration Control is learned through experience It controls the sensitivity of the receiver and distinguishes between AM broadcasts and CW SSB The tuning ranges are set up so that you can expect find something interesting at any time of day or night TO Bands A and B are most active in the evenings Band C has something happening all the time Bands D and E assure a variety of daytime reception but also can be busy night at The audio circuit is designed for one or two pairs of Walkman stereo headphones or mini speakers Other speaker options are mentioned in Section XX 30K D ct d requires removing and replacing the 8 cabinet screws and tha leaving the receiver on overnight will indeed run down th battery If you wish the battery snap wires can be re routed to the battery clamp mounted outside on the rear panel Or the receiver may be powered by larger external batteries in the 6 to 12 volt range 4 to 8 D cells in plastic battery holders available from Radio Shack will provide months of service NOTE If a DC voltage other than 9 vol
20. omical explanation of electronics parts and how they work see Getting Started in Electronics by Forrest Mims No 276 5003 at any Radio Shack store Alignment One time adjustment of internal controls ina radio circuit See also Trimmer AM Amplitude Modulation Band a related group of frequencies Board short for printed circuit board or circuit board Bridge Solder the unintentional joining of two or more points on the solder side of a printed circuit board Carrier the steady tone or whistle that is the foundation of an AM or FM voice signal In most receivers the carrier is not even heard because regeneration or a BFO or direct conversion is required to convert the carrier energy into an audible tone CW Continuous Wave refers to Morse Code signals DC direct current example battery voltage in contrast to household AC from the wall outlet DC sometimes refers to direct conversion receivers see below Detector the section of any radio that changes radio energy into audio energy intended for listening Direct Conversion a popular type of simple receiver for CW SSB which needs no regeneration control but which does not permit pleasant listening to AM shortwave broadcasts because the carrier see above as well as the voice modulation can be heard 21 MFJ 8100 World Band Receiver Electrolytic capacitor a capacitor cont
21. on which eliminates the carrier whistle which you 22 MF J 8100 World Band Receiver hear in an AM broadcast if the Regeneration control is turned too far to the right Tolerance the manufacturing accuracy for electronic and other parts Tolerance ranges from 20 down to better than 1 of the value marked on the part Toroid a type of coil consisting of wire wrapped around a donut shaped form such as L5 in this receiver Trimmer a miniaturized variable resistor or capacitor used for occasional circuit adjustments uF S micro farad the usual unit of capacitance uH micro henry a unit of inductance Sample SWL Logging Page Date Name and Band or Signal Listening UTC GMT Location of Frequenc Quality Notes QSL Broadcast y i service 23 MFJ 8100 World Band Receiver 24 MF J 8100 World Band Receiver MFJ 8100 Parts List Component Number Value Description MFJ Part ced cael adr C1 Air variable 204 5050 P ie 205 0021 200 2016 200 2015 electrolytic Lur a 203 00 c19 470 00 electrolytic LM386 audio amp 311 0386 401 K M 47 uH 401 0015 T 52 2 toroid 403 1003 05 6310 62 4100 1 id 8T ohm pot 162 2250 1 volume 1 22 ohms 1 i E 0 K 25 MF J 8100 World Band Receiver 130 5100 06 0003 Ste
22. one s first regenerative set The reason why this receiver works so well is because ther is much more precision in today s engineering designs and the manufacturing of electronic parts We looked carefully at the practical problems associated with yesteryear s technology and we used TODAY S know how and components to solve the problems A Simplified Explanation of How It Works When you re ready please explore the technical explanation of your receiver in Introduction No 2 In the meantime you can peek at the schematic diagram and picture the receiver in three basic sections A Detector Oscillator 01 02 B RF amplifier Q3 C Audio amplifier IC1 MF J 8100 World Band Receiver To put it very simply a detector converts radio energy from an antenna into audio energy i e a sound which you can hear A detector can be as simple as a crystal diode which is the heart of the simple crystal radio Tf you ve ever heard unwanted radio signals on a stereo telephone PA system or intercom you can assume that some part of those devices has acted as a detector to convert a nearby CB taxi or broadcast signal into intelligible sound This process of detection is also referred to as demodulation In the following explanation the words regeneration feedback and oscillation all mean approximately the same thing By itself a de
23. r performance than many low end factory built superhets of yesteryear Some highlights of our design efforts Significantly reduced RFI back through antenna a chronic regen receiver shortcoming through use of carefully designed RF amplifier stage Effective RF filtering between detector and audio sections of the receiver _ Simplified L C tuning notice that there are 5 band switch positions but no coil taps or second windings Elimination of antenna trimmer so critical in most regenerative designs We replaced the traditional trimmer MF J 8100 World Band Receiver with an RF gain pot that has little effect on frequency or regeneration Manageable tame regeneration control circuit Regeneration begins smoothly with no pop and has a comfortable adjustment range The result we think is a receiver design which bridges the classic simplicity of regeneration to the performance demands of the 1990 s Here s how we did it In brief the circuit uses RF regeneration and high levels of DC feedback Notice that the antenna is coupled directly to the source of RF amplifier FET Q3 rather than through the L C tuning network Direct coupling of the drains of Q1 and Q3 isolates the L C circuit from the antenna input enhancing stability and greatly minimizing RF oscillator output to the antenna Such RFI has been a serious problem in traditional regenerative CLrKCULts which permitted the oscill
24. reo 1 8 jack 601 4010 ttc sw 500 0024 sw2 504 0022 Note C 20 C 22 27 R10 R14 16 R 18 are not used PC Board View 26 MF J 8100 World Band Receiver Schematic Diagram 27
25. tector can interpret or demodulate only very strong signals such as a nearby AM radio station However the process of regeneration can make a detector MUCH more sensitive by turning the detector into an oscillating amplifier The regeneration circuit repeatedly feeds the detected signal back to the input which boosts its strength many hundreds of times This feedback process must be carefully controlled which is the function of the regeneration control The frequency of oscillation is determined by the choice of inductors bandswitch and the setting of the tuning Capacitor If the oscillator is tuned to 10 1 MHz for example any radio signal on that frequency will be boosted and detected in the regeneration process The resulting output from transistor Q2 is a low level audio signal which is boosted to comfortable listening level by the LM386 integrated circuit amplifier The RF amplifier serves two purposes It boosts the RF signals from the antenna to the detector and it minimizes the amount of oscillator RF going back out to the antenna Again we hope you ll also look at the somewhat more technical explanation of how your 8100 Receiver circuit works If any terminology used in this book is unfamiliar to you please check the Glossary For Experienced Hams Enthusiasts or Engineers MF J 8100 World Band Receiver Why use a REGENERATIVE circuit for a kit new for the
26. ts is used readjustment of trimmer C5 will be required correct frequency indications 13 for MF J 8100 World Band Receiver SETTING UP A USEFUL SHORTWAVE ANTENNA The reason why we provided a universal binding post antenna connector plus separate ground connector is to make it as easy and economical for you as possible to try out different antenna setups By universal we mean that you can insert a banana style plug OR make various styles of connection with a simple bare wir Your receiver is so sensitive that even a few feet of wire strung indoors will provide reception of stronger signals particularly at night 20 to 30 feet of wire is much better Therefore you can count on good reception even if you are limited to keeping the antenna indoors as might be required in apartment complexes condos etc Stringing all or part of your antenna outdoors is always better An ideal antenna for this receiver would consist of 25 to 100 feet of wire outdoors as high as is safely possible Such antennas are called random long wires and also work fine in most attics Foil backed insulation or metal roofing will reduc th usefulness of an attic as antenna space Your antenna can be horizontal vertical or a combination of both It can be tubing or pipe as well as wire The wire can be bare or insulated It could be something not intended to be an antenna such as a gutter fence flagpole or
27. u would approach the LSB signal by tuning from higher frequency right to lower left from higher voice pitch to lower pitch Here s how to do it step by step le Pick out a strong high pitched Donald Duck voice 2s Turn the tuning knob ever so slightly to the left 3a If the pitch of the voice went DOWN slightly you re heading in the right direction 4 SLOWLY tune left slightly more until the voice is clear Reverse this process to tune to UP to the right to USB signals on the bands above 7 MHz The Regeneration Control often can be used to do the last touch of fine tuning to bring the voice in clearly If signals are exceptionally strong it may be necessary to reduce the RF gain level rear panel SSB transmissions are used by embassies and agencies of various governments so you might find interesting voice signals on other than ham frequencies Check with a Shortwave Listener SWL or listings in Popular Communications Magazine for more details 12 MF J 8100 World Band Receiver USING amp ENJOYING YOUR RECEIVER To get maximum satisfaction from your new shortwave receiver encourage you to develop good familiarity with these sections of this manual we Antenna Considerations Regeneration Control Band Switch and Tuning Ranges Audio Notes However let s say it all as briefly as possible 1 2 IMPORTANT The internal 9 volt battery will provide man hours
28. uainted with radio communications and electronics as a hobby as a possible profession or both Among the hundreds of publications available we are pleased to recommend the following as especially helpful for radio newcomers and people of any age who are young at heart Getting Started in Electronics by Forest Mims Radio Shack Now You re Talking Discovering the World of Ham Radio ARRL Newington CT 06111 also sold by Radio Shack Plus these MFJ publications Shortwave Listener s Guide for Apartment Condo Dwellers by Ed Noll W3FQJ 1991 MFJ Edition No 36 The Wonderful World of Ham Radio by Richard Skolnik KB4LCS 1990 MFJ Edition No 35 Or if you d like just one copy of one magazine that s all about ALL the signals you may hear on your MFJ 8100 you can find the latest issue of POPULAR COMMUNICATIONS at any serious magazine stand It s a fascinating publication Happy listening SOME HELPFUL WORDS amp ABBREVIATIONS 20 MF J 8100 World Band Receiver Throughout this instruction manual we use plain English as much as possible But there s no way around using common electronics terms and abbreviations where appropriate We simply try to avoid jargon that is unnecessary The following mini glossary was compiled as a help to beginners work with this unit Our descriptions are NOT intended to be complete definitions For a very clear and econ
29. ve broadcast band 13 6 to 13 8 MHz and all of the 19 Meter band 15 1 to 15 6 MHz Station WWV at 15 0 MHz provides precision time and frequency information The 19 Meter band is very good in the morning hours of winter and the late afternoon hours of summer Range E 17 5 to 22 MHz This tuning range is provided to assure good listening variety during daylight hours It includes the 16 Meter broadcasting band 17 55 to 17 9 MHz the 17 Meter ham band 18 068 to 18 168 MHz and the 15 Meter ham band 21 0 to 21 45 MHz Station WWV also broadcasts on 20 MHz SHORTWAVE LISTENING IN GENERAL In addition to the specific bands highlighted above you ll hear thousands of OTHER shortwave signals Many will be military or government Morse code transmissions plus very odd noises of weather FAX wire service and other data transmissions You can also hear government or military SSB voice transmissions and even an occasional unlicensed pirate station A rule of thumb is that the lower frequency ranges A B C are most active during the late afternoon evening and through the night The higher frequencies D and E generally are most active during daylight hours See the conclusion of this book for information on getting more information IN CASE OF DIFFICULTY Following are minor problems which are easy to solve Extremely weak volume on all bands 17 MF J 8100 World Band Receiver
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