Volume Limiting and Distortion Reduction for uBITX #ubitx

jpkellyburbank@...
 

I came up with this mod after testing my 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 I 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 that are stronger than S9+5dBm.  Signals S9+5dBm and weaker are not attenuated.  I've tested with RF input as strong as S9+40dBm (-33 dBm) and get clean output. Now I can 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.

I did a similar mod for the Bitx40 in the past.  This one is tailored to work specifically for the uBITX.  The pin diodes (MA27B) are available at RF Parts Co.

73, ND6P


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