Too much RF up the spout

Jonas SM4VEY posted on the IO GROUPS BITX20 list that his µbitx hadn’t survived field day operations After Jonas discovered his transceiver was dead he connected a dummy load via a power meter as an antenna.

The power meter showed 2 w power into the 50 ohm dummy whenever another nearby station transmitted into a nearby antenna.

His poor µBITx was now as deaf as a brick and provided (almost) no power out on transmit.    Jonas mused “What should I suspect first?”

Constructors made a number of suggestions.  Jonas reported the fixes as follows:

“After replacing the 1st mixer diodes the RX came to life again and I could hear -120dBm signals which represented an improvement of around 30 dB.

“I then started measuring the signal levels before and after each amplification block in the TX path and found Q90 having less signal after, then before.  I replaced Q90 with a leaded transistor and the µBITx now works normally again.

“I’ll look at adding 2 reversed (one each way) diodes to ground from the RX line before the 1st mixer. I’m not sure these will survive 2W though…”

Reference

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