Friday, December 22, 2006

Techies corner 

For anyone interested, this is the 144MHz amateur band SSB transceiver I mentioned in yesterday's post, which I designed and part built about 25 years ago. Apologies for the techie-speak, but all of this is probably only of any interest if you already understand the jargon.

The uppermost PCB is the frequency counter/display driver - the display tubes were salvaged from an old cash register, the chip is a standard device and the PCB, as with all of them, I laid out and etched myself. Next down, on the left, is the IF strip complete with crystal filter, and on the right is the audio board. Below sits the receiver down-converter.

The underside view. At the top is the PCB on which the front panel controls are mounted. In the middle is the phase-locked VCO, underneath which is the battery pack which powers the whole unit; to the right of that is the 2 - 4 MHz VFO to which the VHF VCO is locked, and just below is a switched-mode power convertor which provides supplies at 2V, 5V and 16V from a single 8V battery. The big space to the left is where the transmitter up-convertor and power amplifier would have gone - the only major module I never made.

Detail of the VHF VCO. This produced a VHF signal phase-locked to a very stable low frequency oscillator.

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