MFT-20 DSB Transceiver Kit
Page 2
INTRODUCTION
MFT-20
The MFT-20 “
M
y
F
irst
T
ransceiver” is a simple, low-cost DSB (double sideband) transceiver similar to
the famous “Beach-40”, “Micro-40” by VK3YE, “Wee Willy” by VA3IUL, etc. However, the MFT has
improved both the receive and transmit characteristics, and its kit assembly puts the project within the
reach of radio circuit builders of any level.
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" equipment.
The printed circuit board (PCB) is over-sized for easy location and placement of the components. The
receiver (MFT-RX) can be assembled and put in operation independently of the transmitter, which allows
neophytes to assemble and use the receiver before beginning to work on the transmitter (MFT-TX). The
transmitter cannot operate without the receiver, since the local oscillator is built into the receiver.
The kit can be assembled on a Saturday morning, with time left in the afternoon to go out to the field with
it and make a few QRP contacts.
The MFT-20 incorporates a DC (direct conversion) receiver with a 3-stage front-end passband filter,
followed by a balanced mixer, an audio preamplifier and filter using an operational amplifier, and an
output amplifier for driving a loudspeaker. The local oscillator is based on standard low-cost quartz
crystal of 14.328MHz with which it can be tuned 50KHz or more.
The DSB (double sideband) transmitter uses a DSB generator with input from an economical electret
condenser microphone and three stages of amplification which produce >3W to the antenna.
The simple circuits used make it is possible to enjoy amazing QRP contacts.
The optional
“ILER-DDS”
kit makes it possible to cover the entire band.
The transmitter has a robust design to withstand and work hard in the field!
There are only two controls: RX gain and tuning, which are sufficient for enjoying the pleasure of QRP!
SPECIFICATIONS
GENERAL:
Frequency coverage: High stability quartz Crystal oscillator 14.318MHz which can over 50KHz or more.
Frequency control: Varactor diode.
Antenna: 50 ohms.
Power supply: 12-14VDC, 30mA in receive (without signal), about 1000mA in transmit.
Components: 32 resistors, 2 variable resistors, 67 capacitors, 2 potentiometers (RX-gain/volume and
Tuning), 8 IC's, 5 transistors, 2 inductors-chokes, 6 RF transformers, 5 diodes, 1 quartz crystal.
Front panel controls: Tuning and RX gain.
External connections: mic/ptt, speaker jack, antenna, DC input.
Circuit board dimensions: 110x130 mm.
TRANSMITTER:
RF output: 3W@12V, 3,[email protected].
Second harmonic output: -50dB below the fundamental frequency.
Other spurious signals: all signals -55dB or better below the fundamental frequency.
Carrier suppression: better than -30dB.
T/R switching: Relay.
