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Re: uBitX SSB transmit oscillations on 20m only #ubitx

 

Bruce,

I dont know if you fixed this problem. Here are some ideas.

Try a shielded wire for microphone inside the enclosure. You MUST use shielded wire for the mic cable outside as it may pick up TX RF.

Solder a 1000pf cap across the socket.

Formula I followed in the 70s for mic mixers was to insulate the jack from chassis. You could screw on an acrylic sheet
piece to your panel and mount the mic jack on it.. but you need to enlarge the chassis hole so that the jack does not ground.

Raj

At 28/07/2018, you wrote:
First a correction. The distorted output is on 20m not 40m. Now that's embarrassing! A form of ham dyslexia perhaps?

Audio feedback? Although I had gone through all the bands with no distorted output, I have been mostly comparing 20m with 40m. Distortion-feedback on 20m, clean on 40m. I just went back through all the bands and noticed that I hear a little audio from my speaker as I go up the bands. 80m, 60m, and 40m are good with a clean signal on the 'scope, nothing from the speaker. 20m is badly distorted with feedback and garbled audio from the speaker. 17m and up (in frequency) clean signal but faint audio from the speaker.
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