ND6P Volume limited and distortion reducer

ND6P came up with this mod after testing his uBITX on the bench to determine how much signal it could handle before distorting at the speaker due to clipping of the audio signal.  What he found is that RF input signals greater than S9+5dB (-68 dBm) become distorted due to the audio output clipping on the negative side.

What the mod does is insert enough attenuation at the RF input to prevent the audio from clipping for signals stronger than S9+5dBm. Signals S9+5dBm and weaker are not attenuated. He’s tested with RF input as strong as S9+40dBm (-33 dBm) and gets a clean output.

He says he can now listen to a weak signal without having to reach for the volume control when a strong signal comes on. So effectively this is an automatic RF attenuation circuit to provide AGC functionality for the uBITX.

Points connected to the volume control are in parallel with existing wiring.

The pin diodes (MA27B) are available at RF Parts Co.

Reference

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