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

Don, ND6T
 

I agree. That would be an excellent fix, Pat. But it shouldn't be occurring. Alan, can you take voltage measurements of Q1? From ground to the base, and from ground to collector when transmitting? It seems that the RF is coming in on the 5 volt power, even though it is well bypassed. Lacking a 'scope, a pair of headphones with one side to ground and the other through a .1uF (or so) blocking capacitor will let you listen to the +5 volt supply. I mean putting the capacitor in series with the headphones. The audio amplifier is disconnected from the pre-amp (which is gated off by the "click" board anyway) and is bypassed to ground by C78 (not shown on the schematic). Which brings up a point: Does the volume control affect it at all? Taking the input to U1 to ground by turning the volume all the way down should eliminate it, I would think. Unless it is coming in on the +12 volt supply (which has nothing to do with the AGC).  -Don

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