Re: RFI from uBitx TX after AGC and other mods installed

Mark M

After I sent this it dawned on me to check the 12v supply as well. Sure enough, it's there too. FWIW, I'm powering it off a 20A Astron 13.8v linear power supply and feeding it into my old Heathkit Cantenna dummy load.

I have it installed in one of the cases. The power wiring runs very close to the antenna connection and the final amp transistors. I tried twisting the wires tightly but it didn't make any difference.

If I disconnect the final amp supply line it goes away and there's no noise from the speaker with the AGC board in place.

Anyway, a couple more observations...

Mark AA7TA

On 6/28/18 5:07 PM, Mark M wrote:
I finally had a chance to start looking into this on my ubitx (I'm seeing the same issue). I managed to borrow a scope and putting it on the 5v supply seems to indicate that you're right. I see up to about 40 mv p-t-p on the 5v line when xmitting SSB with the AGC board not connected at all. It's pretty clean in receive. I'm tapping into the 5v line on the raduino. So that certainly looks like the smoking gun.
Now to figure out how it's getting in there...
Hope this helps...
Mark     AA7TA

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