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Hi friends,

I'm continuing to make slow, but steady progress on the homebrew SBITX.? ?The most recent issue resolved was self-oscillation in the WM8731 codec on CW key down.? You could hear the CW sidetone in the speaker but with lots of distortion - also visible in the RF.? The fix to that was to swap out the MIKROE codec board.? The new board did not exhibit that problem.? ?But I have an ogoing problem wiht intermittent Tx which was happening on either board.

The issue is this.? On CW keydown one of four things happens:

1. Nominal case - I hear audio out from the speaker and see RF all the way through to the antenna.? All is well.
2. Audio only - no RF.? that means one output channel of the DAC getting signal but the other is not,
3. No audio and no RF,? the rig goes into transmit - you can see it on the SBITX spectrumb -? but nothing comes out either DAC port
4. RF but no audio - this has happened only once or twice

demonstrating what I am talking about.

Has anyone experienced anything similar???

73,
Dean
KK4DAS

Well. Clearly it's getting RF somewhere and doing something it shouldn't. Rearrange all your earths. Do a bit of shielding and get stuck in with a handful of 100pfs. Point your bum at the sun and pray for a good result ... Good luck.?

73 de Ian, MI5AFL?

On Sun, Apr 14, 2024 at 03:32 PM, Ian McCrum MI5AFL wrote:

Clearly it's getting RF somewhere and doing something it shouldn't

Ian,

What makes you believe this is an RFI problem?? The symptom is not getting AF out of the codec DAC ports.? Have you seen this problem before with either the MIKROE prototype board or with any other WM8731 board??

73,
Dean
KK4DAS