At 12:54 AM 6/23/2010, Leigh L. Klotz, Jr WA5ZNU wrote...
At the local flea market, I picked up what appears to be an Efratom FRS-C. It is marked "TTL" internally. It has the passive connector board, but not the active board with the 15 MHz synthesizer on it.
Connector board? No such beast described in the manual. Do you mean the A3 power supply board, which has the i/o connector on it?
Active board? Ditto. Do you mean the A4 oscillator board, which has a 20 MHz VCXO on it? There's no 15 MHz anywhere in an FRS-C.
Here's a manual: http://www.to-way.com/tf/frs.pdf
Mine is marked "TTL" internally. The service manual has a chart showing the differences between the sine and TTL options, and I converted it to the sine version by changing a jumper to a resistor and populating an LC filter with 10uH and 100pF (~5 MHz). I also terminated the RF connection on the connector board with a 47 ohm resistor to ground.
It sounds like you made the changes to the A4 oscillator board, but not the ones to the A3 power supply board (several inductors, resistors and caps). I found that using a 1 uF for C16, instead of the documented 0.1 uF, gives a better signal. See the top of page A-15 in the manual.
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