BITX20 Update #28

I did some more tidying up on my BITX20 during the week. I re-routed some of the internal cables so I can now lay the top and bottom of the case flat and work on the radio.

I also wired up a speaker/microphone via the front panel connection. This has created another problem. When the PTT is pressed there is a loud squeal from the speaker for about 1 second.

This is caused because the receive audio section is still powered when the transmit audio section starts being powered. There is a short overlap causing the microphone and speaker to feedback, and since they are in the same enclosure, I can’t separate them.

To overcome this issue I am thinking of adding a transistor somewhere in the microphone amplifier to prevent the audio passing until the receive DC power has gone.

I could also add a relay to switch out the speaker/switch in the microphone but that would add to the overall current consumption.

I have also noticed a new problem with the PA3CNO display circuit. When I lock the frequency in receive mode and then press the PTT the huff and puff circuit unlocks. I am not sure if this is because of a voltage spike issue or a VFO frequency spike issue. I will look at this soon.


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