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MFJ VEC-102K Assembly Manual

World band receiver
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VEC-102K World Band Receiver
Instruction and Kit Assembly Manual

Table of Contents

Receiver Features ...................................................................................................... 2
Introduction No. 1: For Beginners............................................................................ 3
Introduction No. 1: For Hams, Experienced Experimenters .................................... 6
Schematic Diagram of VEC-102K............................................................................ 8
Receiver Controls...................................................................................................... 9
Understanding and Using the Regeneration Control................................................. 11
Tuning SSB Voice Signals ........................................................................................ 12
Some Helpful Terms & Abbreviations...................................................................... 13
VEC-102K Parts List ................................................................................................ 15
PC Board X-Ray View .............................................................................................. 17
Before You Start Building......................................................................................... 18
Phase 1 (steps 1-1 to 1-10) ........................................................................................ 19
Phase 2 (steps 2-1 to 2-20) ........................................................................................ 20
Phase 3 (steps 3-1 to 3-20) ........................................................................................ 22
Phase 4 (steps 4-1 to 4-14) ........................................................................................ 23
Phase 5 (Testing and Initial Adjustment) .................................................................. 25
Phase 6 (Final Assembly, Adjustment of C5) ........................................................... 27
Dial Calibration Adjustment of Timmer Capacitor C5............................................. 29
Note to Hams or Experimenters ................................................................................ 29
Using and Enjoying Your Receiver........................................................................... 30
Setting Up a Useful Shortwave Antenna................................................................... 31
Power Receiver's Audio Circuit ................................................................................ 31
About the 5 Tuning Ranges of Your Receiver .......................................................... 32
Shortwave Listening in General ................................................................................ 33
In Case of Difficulty.................................................................................................. 34
Notes for Radio Hams & Experimenters................................................................... 35
Conclusion................................................................................................................. 36

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  • Page 1: Table Of Contents

    Receiver Features ...................... 2 Introduction No. 1: For Beginners................3 Introduction No. 1: For Hams, Experienced Experimenters ........6 Schematic Diagram of VEC-102K................8 Receiver Controls...................... 9 Understanding and Using the Regeneration Control..........11 Tuning SSB Voice Signals ..................12 Some Helpful Terms &...

  • Page 2: Receiver Features

    VEC-102K 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 economical "personal stereo" headphones or speakers •...

  • Page 3: Introduction No. 1: For Beginners

    Introduction No. 1: For Radio 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 variety of international broadcasts.
  • Page 4 Back to Today . . . and the Future! Your VEC-102K 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 one's first regenerative set.
  • Page 5 RF going back out to the antenna. Again, we hope you'll also look at the somewhat more technical explanation of how your VEC-102K Receiver circuit works. If any terminology used in this book is unfamiliar to you, please check the "Some Helpful Word & Abbreviations" section.

  • Page 6: Introduction No. 1: For Hams, Experienced Experimenters

    Why use a REGENERATIVE circuit for a kit new for the 1990's? A fair question, but the VEC-102K is not like any regenerative HF receiver you've ever used before! Our GOAL determined the design and circuitry of this receiver. We wanted the following features: •...
  • Page 7 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.

  • Page 8: Schematic Diagram Of Vec-102K

    Schematic Diagram...

  • Page 9: Receiver Controls

    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.
  • Page 10 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.

  • Page 11: Understanding And Using The Regeneration Control

    Understanding & 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.

  • Page 12: Tuning Ssb Voice Signals

    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. 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.

  • Page 13: Some Helpful Terms & Abbreviations

    Some Helpful Words & Abbreviations Throughout this instruction manual, we use plain English as mush 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 working on this kit.
  • Page 14 Install: in modern kit building, this ward means 1. Select correct part 2. Insert it in its circuit board position, oriented correctly. 3. Solder all points 4. Trim or nip away excess wire lengths K: abbreviation for 1000 ohms. (10K = 10,000 ohms). KHz: KiloHertz, a thousand hertz MHz: MegaHertz, a million hertz Inductor: A coil or loop or wire used in electronic circuits.

  • Page 15: Vec-102K Parts List

    VEC-102K Parts Lists Please check and organize your kit parts before soldering. FIXED CAPACITORS 1 - 33pF disc [C6] 1 - 47pF monolithic (marked 47 or 470) [C3] 1 - 75pF disc [C16] 2 - .0033µF polystyrene (rectangular) [C9,C17] 4 - .01µF disc (marked 103Z) [C7,C8,C21,C28] 5 - .1µF DISC (marked 104Z) [C2,C4,C10,C11,C15]...
  • Page 16 2 - PC-mount 1/8" stereo phone jack [J2,J3] 1 - Insulated binding post (antenna) [J1] 1 - PC-mount push-button switch (DC on/off) [SW2] 1 - 5-position rotary switch (bandswitch) [SW1] HARDWARE & MISCELLANEOUS 1 - Pre-drilled printed circuit board 1 - 9-volt battery snap connector 1 - 9-volt battery bracket with foam adhesive strip 1 - Aluminum chassis (bottom section) 1 - Aluminum cover...

  • Page 17: Pc Board X-Ray View

    "X-Ray View" of Printed Circuit Board...

  • Page 18: Before You Start Building

    Before You Start Building! Your receiver is designed to work perfectly as soon as correct construction is completed. Before we get started, let's explain exactly what we mean by "correct" construction. If you understand potential and typical problems before you build, chances are that you won't make those classic mistakes which can frustrate electronic kit builders.

  • Page 19: Step-By-Step Kit Construction

    STEP-BY-STEP KIT CONSTRUCTION You'll build your receiver in six phases in this order: 1. Small parts associated with bandswitch and tuning 2. Transistor RF amplifier and detector section 3. IC audio amplifier 4. Controls, switches, jacks 5. Testing and initial adjustment 6.

  • Page 20: Phase 2 (Steps 2-1 To 2-20)

    Note: The L5 inductor for Band E is a wind-it-yourself "toroidal coil" (don't worry: it's easy!) which we'll make and install in Phase 5 so that it is not subjected to bumping and bending during other assembly. 1-6. Install R4, 10K (brown-black-orange). Its position is between L1 and L2. 1-7.
  • Page 21 2-8a. The locations for all three FET transistors (Q1, Q2, Q3) are imprinted clearly on the PC board. Notice the flat and rounded sides of the imprints, corresponding exactly to the shape of the transistors viewed from the top. We'll install all 3 transistors in the following steps. (1.) Simply press each one into its 3 holes as far as it can reasonably go, (2.) gently bend the leads outward to secure it, (3.) solder all three connections, and clip away the excess wires.

  • Page 22: Phase 3 (Steps 3-1 To 3-20)

    Construction Phase 3 (Steps 3-1 through 3-20) The following group of parts form the audio amplifier circuit which boosts the signal from the FET transistors to useful listening volume. 3-1a. Examine the 8-pin socket for the LM386 IC and notice the rectangular notch at one end.

  • Page 23: Phase 4 (Steps 4-1 To 4-14)

    About the Jumper Wires Several lengths of hookup wire are installed on the top side of the board between points marked W1, W2, etc. The purpose of such "jumper wires" is to make efficient connections across circuit traces on the solder side of the PC board in situations where running a circuit board trace would not be efficient.
  • Page 24 4-3. Install headphone jack J3 per 4-1 (above). 4-4. Install SW2, the power on/off push-button switch per 4-1. 4-5. Install R2, the 250 ohm volume control per 4-1. It is clearly stamped "250" on its back. 4-6. Install R1, the 10K ohm regeneration control per 4-1. Note on C1: The rotor (moveable) section of C1 is electrically common with the frame and therefore the four bottom pins which are soldered to the receiver ground plane.

  • Page 25: Phase 5 (Testing And Initial Adjustment)

    (Steps 5-1 through 5-11) Testing and Initial Adjustment Congratulations! If you performed Steps 1-1 through 4-13 successfully, your finished VEC-102K is already a working shortwave receiver! To be assured of satisfactory receiver performance, PLEASE continue following our step- by-step directions.
  • Page 26 5-5. Make a temporary connection of your antenna or a 10-20' length of any kind of wire to the short antenna wire near the RF gain control. 5-6. Set the RF Gain trimmer to about 3/4 fully clockwise (as viewed from the rear of the PC board).

  • Page 27: Phase 6 (Final Assembly, Adjustment Of C5)

    Now, use a small screwdriver (or just your finger on the plastic wheel) to adjust trimmer R20 to the point where regeneration just begins, with all other controls set as specified above. (This adjustment will be touched up after the receiver is assembled into its cabinet.) 5-11.
  • Page 28 6-10. After making sure that everything lines up square and attractively, tighten the three panel nuts, taking great care not to scratch the front panel. 6-11. Turn the Tuning capacitor to the left until the plates are visibly meshed. Press the dial pointer, black washer first, (pointing exactly left) onto the capacitor shaft.

  • Page 29: Dial Calibration Adjustment Of Timmer Capacitor C5

    Note to Hams or Experimenters A very easy method for adjusting C5 is to listen for the VEC-102K's oscillator on a nearby receiver or transceiver. Even with no antenna wire connected to the VEC-102K, the oscillator is easily heard within a range of 10-15 feet.

  • Page 30: Using And Enjoying Your Receiver

    While a single adjustment of C5 can be made using any reference frequency, it's a good idea to use your test equipment or other receiver to verify approximate tuning accuracy on all 5 bands. If one or more bands are drastically wrong, be sure to check for correct inductor values and good solder connections of the inductors.

  • Page 31: Setting Up A Useful Shortwave Antenna

    Note: If a DC voltage other than 9 volts is used, readjustment of trimmer C5 will be required for correct frequency indications. 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.

  • Page 32: About The 5 Tuning Ranges Of Your 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.

  • Page 33: Shortwave Listening In General

    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.'' Range A: 3.5 to 4.3 MHz.

  • Page 34: In Case Of Difficulty

    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.

  • Page 35: Notes For Radio Hams & Experimenters

    You'll quickly gain the skill of finessing the regeneration control to choose AM shortwave broadcasts, SSB or CW/RTTY. The VEC-102K just might be the very best regenerative receiver ever designed, but it is not intended to be all things to all people.

  • Page 36: Conclusion

    The author conducted a few simple tests using an HW-9 for transmitting, side by side with the VEC-102K on 30, 20, 17 and 15 meters. You will want T-R switching to short the receiver antenna input to ground and also to mute the audio.
  • Page 37 COMMUNICATIONS at any serious magazine stand. It's a fascinating publication. Happy listening!

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