MFJ-8100K_user.pdf

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1、 MFJ-8100 World Band Receiver Instruction and Kit Assembly Manual Table of Contents Receiver Features.2 Introduction No. 1: For Radio Beginners.3 Introduction No. 1: For Experienced Hams, Enthusiasts or Engineers.6 Schematic Diagram of MFJ- 8100.8 Receiver Controls and Connectors.9 Understanding and

2、 Using the Regeneration Control.11 Tuning SSB (Single Sideband) Voice Signals.12 Some Helpful Terms and Abbreviations.13 MFJ- 8100 Parts List.15 X- Ray View of Printed Circuit Board.17 Before You Start Building !.18 STEP- BY- STEP KIT CONSTRUCTION (19- 28) Construction Phase 1 (steps 1- 1 through 1-

3、 10).19 Construction Phase 2 (steps 2- 1 through 2- 20).20 Construction Phase 3 (steps 3- 1 through 3- 20).22 Construction Phase 4 (steps 4- 1 through 4- 14).23 Construction Phase 5 (steps 5- 1 through 5- 11).25 Testing and Initial Adjustment Construction Phase 6 (steps 6- 1 through 6- 18).27 Final

4、Assembly Dial Calibration Adjustment of Trimmer Capacitor C5.29 Note to Hams or Experimenters.29 Using and Enjoying Your Receiver.30 Setting Up a Useful Shortwave Antenna.31 Your Receivers Audio Circuit.31 About the 5 Tuning Ranges of Your Receiver.32 Shortwave Listening in General.33 In Case of Dif

5、ficulty.34 Notes for Radio Hams and Experimenters.36 Conclusion.37 Circuit Component Index.38 2 MFJ-8100 Receiver Features Five separate tuning ranges between 3.5 and 22 MHz. Smooth 6:1 vernier- reduction tuning dial Sensitive FET RF amp and detector stages Dual headphones for sharing the fun Use ec

6、onomical personal stereo headphones or speakers Smooth, well- engineered regeneration circuit True choice of AM- CW- SSB reception Excellent reception even with a few feet of wire antenna + + + + VERY IMPORTANT PLEASE READ: Your receiver carries MFJs respected No Matter What guarantee specifically t

7、o the extent that you may return the entire kit UNASSEMBLED for credit or refund. If you have never built an electronics kit before, PLEASE study this book carefully before unpacking the small parts. Once you have begun soldering parts, neither MFJ or any dealer can accept the return of the kit for

8、any reason whatsoever. MFJ- 8100 World Band Receiver Instruction and Kit Assembly Manual Instruction Manual developed and designed by Dan F. Onley, K4ZRA Copyright 1993 by MFJ Enterprises, Inc. All Rights Reserved. No part of this work may be copied or reprinted without the explicit permission of th

9、e copright owner. MFJ Enterprises, Inc. 300 Industrial Park Road Starkville, MS 39759 Printed in the United States of America. 3 Introduction No. 1: For Radio Beginners Youre about enjoy a versatile shortwave receiver which employs a circuit concept that is as classic as the 1920s but which uses mod

10、ern engineering that takes advantage of the advanced capabilities of todays electronic components. This shortwave radio is designed to let you listen to a great variety of international broadcasts. You can choose from five different frequency bands so that you can count on hearing SOMETHING at any h

11、our of day or night. Also, this receiver lets you hear a generous sampling of ham radio signals (both Morse code CW and voice SSB communications), plus many other government and commercial transmissions. Even if you have never worked with electronic parts before, you can successfully build this rece

12、iver by carefully following all the directions in this book. Step by step, well show you how to build it and how to enjoy it. Before you start building however, please read the notice on page 2 so that there is no misunderstanding about your rights as a valued MFJ customer. Just a Bit of History . .

13、 . 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, these magical, whistling, squawking, glowing boxes were the norm for home listening as well as for the first generation

14、 of radio hams. Receiver design evolved swiftly. The superheterodyne became the norm during the 1930s. 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, touc

15、hiness, 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 a

16、nd beginners. In fact, as recently as the 1960s, one company marketed a $14 kit for building a complete transceiver using only 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 engi

17、neering careers as well as ham radio licenses were launched with the building of my first shortwave radio from do- it- yourself regenerative 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 affor

18、d to move up to a superhet communications receiver. Their fondest memory TODAY is that very first receiver kit.) 4 From the late 1970s through the 80s, as consumer electronics and new ham radio equipment became more sophisticated so very rapidly, interest declined not only in regenerative receivers,

19、 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

20、- 8100 is a much better receiver than the classic radio sets which attracted several generations of Americans to the excitement 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 ones first re

21、generative set. The reason why this receiver works so well is because there is much more precision in todays engineering designs and the manufacturing of electronic parts. We looked carefully at the practical problems associated with yesteryears technology, and we used TODAYS know- how and component

22、s to solve the problems. A Simplified Explanation of How It Works When youre 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 (Q1,Q2

23、) B. RF amplifier (Q3) C. Audio amplifier (IC1) 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. If youve ever heard unwanted ra

24、dio 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, t

25、he words regeneration, feedback and oscillation all mean approximately the same thing. By itself, a detector 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 in

26、to 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. 5 The frequency of oscillation is dete

27、rmined 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 sign

28、al 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 youll also look at

29、 the somewhat more technical explanation of how your MFJ- 8100 Receiver circuit works. If any terminology used in this book is unfamiliar to you, please check the Some Helpful Word notice that there are 5 band switch positions but no coil taps or second windings! Elimination of antenna trimmer so cr

30、itical in most regenerative designs. We replaced the traditional trimmer 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. 7 The result, we think, is

31、 a receiver design which bridges the classic simplicity of regeneration to the performance demands of the 1990s. Heres 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 tha

32、n 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 circuits which permitted the

33、 oscillating detector to behave as an unstable but potent QRP transmitter. R4 reduces the Q of L1 (10 H) 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

34、so forth. Air variable C1 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 individu

35、al 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 au

36、dio section. The LM386 (IC1) circuitry employs all recommended options for maximum gain and protection from self- oscillation. To prolong useful battery life, R13 limits current draw by the LED (CR1) to minimum reasonable visibility as an on/off indicator. 9 Receiver Controls and Connections Most of

37、 the controls are self explanatory. However, it is very important to understand the correct use of the Regeneration 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

38、 scale. TUNING (C1) The Tuning knob controls an air- variable capacitor (C1) 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 t

39、he 10% tolerance ratings of the fixed inductors (L1 through L5). PUSH SWITCH (SW2) AND LED. 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 under

40、standing and controlling regeneration is at the heart of your receivers performance, weve 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 contro

41、l. 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 (R19) This trimmer potentiometer is adjustable with a small screwdriver. Maximum gain is clockwise when viewing the rear

42、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 R19 at its maximum setting. If you are using a very good antenna (a long, high outdoor wire or ham antenna), keep R19 at about 2/3 or so of its range. If your listening

43、interests require frequent RF gain adjustments, install an external 10K control in series with your antenna. 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 Constr