My BitX20 Choice.

Started by gil, May 24, 2015, 10:29:51 pm

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NavySEAL

Gil......what is the latest on chasing down the problem?

gil

Hello,

I was gone for three days, but ready to get back to it now.

The receiver section seems to work fine, I hear QSOs, though the volume
is very low. Yes, I've peaked the band pass filter the best I could.

I went through the finals biasing routine with no trouble, 120mA on
receive, 300mA PTT on.

Then I got to the transmitter drive with R83, nothing!

I tested the microphone with a guitar amp, it worked. Connected the
microphone and tested again at the mic leads, played a tone through my
phone and a signal generator app near the mic, got only a faint tone at
full volume on the amp. No output on my QRP Wattmeter, even with R83
fully clockwise. No change, 300mA.

I checked Q15, 0.7V between emitter/base, 3.8V at collector/base, no
audio picked up at the collector with the guitar amp. R76 does get the
+12V when PTT. All components in the mic preamp are in the right place.

With R66 fully counter clockwise and R83 fully clockwise, I get 0.4W out
whether to tone is on or not. R66 controls carrier suppression, so I do have a carrier at least..

Next step might be to inject a tone after the mic preamp and see what happens..

I'll put a link to the manual below, with the schematic, in case anyone wants to have a crack at it..
http://qrpkits.com/files/BITX20_Assembly_Manual.pdf

Gil.