144 Mhz DSB Transceiver Idea

This is just an idea for a simple 2m DSB transceiver, I'm still thinking about this one. 
Using the circuit of the 6m QRP DSB Handy Transceiver(Micro6DSB) from JR8DAG
Using a 72Mhz xtal in place of the 50Mhz and changing the single balanced mixer/modulator
to a sub-harmonic mixer, the circuit should work on 2m without any other mods except for the tuned circuits.

144 Mhz DSB Transceiver

The JR8DAG design did not work out, and after some considerable tinkering with various ideas and circuits
of my own, I finally got a working transceiver (shown below).

The receiver is direct conversion using 3xBF199 transistors, and the tx balanced modulator uses a similar circuit.



Boards from left to right; tx/rx control, vxo, transmitter, receiver.

Receiver schematic
Transmitter schematic
VXO Schematic




The vxo is housed in a shielded box.

I did try using the SA602 ic, and while they worked fine, I thought it would be more of a challange using common bipolar transistors.
All rf transistors are BF199 except for the tx pa which is a 2N4427, all other transitors are of the BC547/557 variety.

Circuit Description
The Receiver:
The rf amplifier is a simple common emitter amplifier using a BF199, this is followed by the product detector using 3 x BF199 transistors.
The audio from the product detector is passed through a simple low pass filter to the audio preamplifier using a BC549C transistor, then on to
the audio amplifier using an LM386.

The Transmitter:
The audio from the microphone is amplified by the BC547 modulator, and is feed into the balanced modulator made with 3 x BF199
transistors, the output from the balanced modulator feeds into the pa driver using another BF199 this feeds into the power amplifier
using a 2N4427.

The Vxo:
The vxo comprises a 24Mhz collpitts oscillator with buffer using 2 x BC547 transistors, this feeds into the 6 x multiplier using a
BF199, the output then passes through a 144Mhz bandpass filter and is switched between the transmitter and receiver with a simple
diode switch.

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Last update: 5/6/2011