MFJ Enterprises 8100w World Band Receiver Manual
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MFJ-8100 World Band Receiver 1 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 & Experimenters Page 13 Conclusion Page 14 Some Helpful Terms & 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
MFJ-8100 World Band Receiver 2 Instruction Manual written by Dan F. Onley, K4ZRA Copyright 1993 by MFJ Enterprises, Inc. All Rights Reserved.
MFJ-8100 World Band Receiver 3 For Beginners Youre about enjoy a versatile shortwave receiver which employs a circuit concept that is as classic as the 1920s but which uses modern 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 hour 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. 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, these 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 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, 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 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 engineering careers as well as ham radio licenses were launched with the building of my first shortwave radio from do-it-yourself regenerative
MFJ-8100 World Band Receiver 4 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 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, 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 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 regenerative 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 components 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) B. RF amplifier (Q3) C. Audio amplifier (IC1)
MFJ-8100 World Band Receiver 5 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 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 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 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 youll 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
MFJ-8100 World Band Receiver 6 Why use a REGENERATIVE circuit for a kit new for the 1990s? A fair question, but the MFJ-8100 is not like any regenerative HF receiver youve ever 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 ICs Purposeful choice of tuning ranges for SWLing anytime. Satisfactory AM-CW-SSB listening and circuit simplicity were our primary goals. Despite the popularity of NE602-type direct conversion circuits among todays 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 refine the 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 better 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
MFJ-8100 World Band Receiver 7 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 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 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 circuits which permitted the oscillating 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 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 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.
MFJ-8100 World Band Receiver 8 To prolong useful battery life, R13 limits current draw by the LED (CR1) to minimum reasonable visibility as an on-off indicator.
MFJ-8100 World Band Receiver 9 RECEIVER CONTROLS AND CONNECTIONS Most of 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 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 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 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 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 (R9) This trimmer potentiometer is adjustable with a small screwdriver. 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 R9 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.
MFJ-8100 World Band Receiver 10 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,J3) 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 (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 & USING THE REGENERATION CONTROL In theory, your receivers 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 todays 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.