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EA3GCY MFT-20 Assembly Manual

20 meters dsb transceiver kit
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MFT-20
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ransceiver
20 Meters DSB Transceiver Kit
Assembly manual
Last update: June 1, 2017
ea3gcy@gmail.com
:
Most recent updates and news at
www.ea3gcy.com
Thanks for constructing the MFT-20 DSB Transceiver kit
Have fun assembling it and enjoy QRP!
73 Javier Solans, ea3gcy
MFT-20 DSB Transceiver Kit
Page 1

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  • Page 1 Assembly manual Last update: June 1, 2017 ea3gcy@gmail.com Most recent updates and news at www.ea3gcy.com Thanks for constructing the MFT-20 DSB Transceiver kit Have fun assembling it and enjoy QRP! 73 Javier Solans, ea3gcy MFT-20 DSB Transceiver Kit Page 1...

  • Page 2: Specifications

    The MFT-20 is a transceiver designed especially for new builders, for educational use in schools and for club building projects and the like. However, it is also a very attractive assembly project for experienced amateurs who like low power and want to get on the air with "minimalist"...

  • Page 3: Tips For First Time Builders

    There are two important things which need to be done to insure successful operation of a kit. The first is to put the component into the proper place on the circuit board; the second is good soldering. MFT-20 DSB Transceiver Kit Page 3...
  • Page 4 Look for the most appropriate moment to do it, and most importantly, take your time. The drawings and instructions in the manual will illustrate and accompany you in the process. MFT-20 DSB Transceiver Kit Page 4...

  • Page 5: Parts List Sorted By Value/Quantity

    22P, 22pK or 22J C3, C5 8P2 or 8.2 220uf C66 (elec.) 220uf 25v or 35V 100uf C23, C24 (elec.) 100uf 25V or 35V 10uf C11, C16, C15, C20, C42, C45, C55 (elec.) 10uf 25V 35V MFT-20 DSB Transceiver Kit Page 5...
  • Page 6 95 cms enameled copper wire 0,3mm for L4 Electret mic Electret Microphone capsule MFT PCB 110mm x 130mm MFT PCB * Pins listed in small print are only placed if the receiver is built independently (without the transmitter). MFT-20 DSB Transceiver Kit Page 6...
  • Page 7 Circuit section Located 100n 104 or 0.1 RX antenna Input H-10 82 or 82J Rx passband J-10 8p2 or 8.2p Rx passband J-11 82 or 82J Rx passband J-10 8p2 or 8.2p Rx passband J-10 MFT-20 DSB Transceiver Kit Page 7...
  • Page 8 104 or 0.1 Output Amp Bias A-8/9 100n 104 or 0.1 Output Amp A-8/9 220p poly B-8/9 470p poly B-10 220p poly B-11 220uF 220uF electrolytic Relay Tx/Rx switch 100n 104 or 0.1 Relay Tx/Rx switch MFT-20 DSB Transceiver Kit Page 8...
  • Page 9 FT37-43 toroid 10t - 3t see text Driver C/D-8 100uH axial inductor brown-black-brown Output Amp Bias C-6/7 FT37-43 toroid 8+8 see text Output Amp A/B-7/8 T37-2 Turns = see text T37-2 Turns = see text B-10/11 MFT-20 DSB Transceiver Kit Page 9...
  • Page 10 143-QUADRANT COMPONENT LAYOUT MAP MFT-20 DSB Transceiver Kit Page 10...

  • Page 11: Recommended Assembly Sequence

    The values which are in decade increments can be easily confused, such as 470, 4K7 and 47K, so be sure to verify the colors before soldering the component in place! If you are in doubt, use a multimeter to check the resistor value. MFT-20 DSB Transceiver Kit Page 11...
  • Page 12 D1 is 1N4148; it is normally orange in color with a black band and has the type “4148” printed on the body. D3 is a 47V zener diode. It is marked as BZX85C47 or Z47. MFT-20 DSB Transceiver Kit Page 12...
  • Page 13 The electrolytic capacitors must be placed with the correct orientation: the LONG LEAD goes in the hole labeled “+” and the SHORT LEAD is "-", indicated by a band containing "-" signs on the side of the capacitor.     MFT-20 DSB Transceiver Kit Page 13...
  • Page 14 It is also recommended to apply a dab of thermal grease on both sides of the mica sheet. Note that the screw goes through the heatsink's upper hole. MFT-20 DSB Transceiver Kit Page 14...
  • Page 15 IC can cause malfunction of the kit. Now, place and solder the voltage regulators IC4, IC7 (78L06) and IC8 (78L08) in their respective locations according to the markings of the component outline on the circuit board. MFT-20 DSB Transceiver Kit Page 15...
  • Page 16 Counting the turns: Count one turn for every time the wire passes through the center of the toroid. Important: wind the toroid exactly as shown in the pictures. MFT-20 DSB Transceiver Kit Page 16...
  • Page 17 “c” and “d” facing towards L8 and C53 (place exactly as shown in the pictures). Counting the turns: Count one turn for every time the wire passes through the center of the toroid. MFT-20 DSB Transceiver Kit Page 17...
  • Page 18 - Cut a 31-32cm (12in) long piece of 0.5mm diameter enameled wire. - Bend the wire in half. - Twist it so that there are about two twists per cm. 16cm (32 cm bent in half) MFT-20 DSB Transceiver Kit Page 18...
  • Page 19 - Mount the toroid into the appropriate holes as marked on the circuit board. Note: For greater clarity, the drawing shows one black wire and one red wire. In reality, both wires are of the same color. MFT-20 DSB Transceiver Kit Page 19...
  • Page 20 IMPORTANT: DO NOT MOUNT toroid L4 yet. It will be installed later, in the last section for adjustment and testing.        MFT-20 DSB Transceiver Kit Page 20...

  • Page 21: Adjustments And Tests

    Connect a frequency counter to the “VXO” header. If the input of the frequency counter is low impedance, insert a 470 ohm (or greater) or a small value capacitor (try with 22pF or less) between the frequency counter and the header to reduce the interaction with the VXO. MFT-20 DSB Transceiver Kit Page 21...
  • Page 22 VXO frequency (20m band) and that has digital frequency readout. Connect to the receiver antenna input a piece of wire with a small loop and place it close to the MFT-20. Spreading or compressing the turns of L4 changes slightly the range of coverage. Compressing the turns increases the inductance, thus increasing the frequency range.

  • Page 23: Useful Notes

    Although 50-60KHz can be tuned perfectly with a one-turn potentiometer and a large diameter control knob. You have the possibility to replace the potentiometer by a 10-turn or add a mechanical reducer dial (see components at www.ea3gcy.com) MFT-20 DSB Transceiver Kit Page 23...
  • Page 24 20 meters band Antenna To obtain a good performance of the MFT-20, it is essential to use a specific antenna for the 14MHz band. You can use a special factory ham radio antenna. Or you can build your own dipole antenna for very little money and that will give you very good results.
  • Page 25 The connection scheme is very simple: Or you can build your own handheld microphone with the micro electret capsule included in the kit and a pushbutton for PTT (not included): Mic “home made” Handheld mic optional (ea3gcy.com)  MFT-20 DSB Transceiver Kit Page 25...

  • Page 26: If Your Kit Does Not Work After Assembly

    - If you decide that technical assistance is needed, you are welcome to send an email to ea3gcy@gmail.com. As a last resource, you may send the kit in for repair; however, I will have to charge for any repairs done, although I will try to keep the cost as moderate as possible.

  • Page 27: Limited Warranty

    Please, BEFORE returning a product, request instructions by email at: ea3gcy@gmail.com Javier Solans, EA3GCY, warrants this device to function according to the specifications, provided that it is assembled and adjusted as described in this documentation, and used correctly according to all provided instructions.
  • Page 28 SCHEMATIC MFT-20 DSB Transceiver Kit Page 28...
  • Page 29 Note that if you use the RX along with the TX, you do not have to connect anything in “VFO-TX”, “+V”, “+VRX”, “+VTX” and “RX-ANT” terminals. The "VFO-TX" and "VTX" terminals are arranged to use a different transmitter. MFT-20 DSB Transceiver Kit Page 29...
  • Page 30 WIRING (To use RX only) MFT-20 DSB Transceiver Kit Page 30...
  • Page 31 The MFT-20 transceiver wiring is very simple, as long as you remember that: - For the antenna connection use a thin, RF-rated coaxial cable such as RG-174 or similar. - If you install the tuning polyvaricon off the circuit board, you should use short and stiff wires, as the mechanical stability is very important.

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