Thursday, November 1, 2012

While trouble-shooting my BitX20 I realized the VFO was oscillating at twice the frequency. Turns out the VFO inductor, which happened to be half of a FM IF coil, was suppose to be rewound to obtain the correct  frequency. So I replaced it with a toriod wound with 50 turns and it it was pretty close to the correct frequency.

I still had problems with the audio circuit. After closely looking at the the schematic and actual circuit, I notice the an electrolytic cap was installed wrong. That made it better but it still oscillated, but only when the volume control was not fully turn to either the full on or full off position. (A clue)

I decided to look at the output of the transistor that drives the audio amp with a scope. Guess what? It stopped oscillating! Another clue! I assumed the probe capacitance neutralized the circuit, so I soldered a 220pf cap(because that was the smallest I had)  from the transistor collector to ground and that has solved the problem for now.

So I got the receiver working somewhat now for the transmitter. More to come!!