Message #15140 posted to https://groups.io/g/ic756pro3
by Matt Erickson KK5DR on 9 June 2007.


Most of us have heard or experienced the distortions present in the Pro II & III and several other models of DSP based radios. 

I wondered if a procedure to work around this problem could be developed. 
I was using my Pro III and filter selection below 250Hz down to 50Hz on CW.
With no pre-amp or attenuation A small amount of "cellophane" distortion
can be heard. AGC selection had little effect on it. 

What I did was to use the "dBm from Heaven" method. (https://www.ab4oj.com/icom/dbmheaven.html) I decreased RF gain to the point where the only signal that could be heard was the single CW signal. Nearly all of the distortions were gone at this point. 

TheCW signal I was listening to was S-1 before I did the procedure. I also tried using the attenuator to the same effect. I used the pre-amps, and combined it with reduced RF gain and attenuators all to the same effect.

So, if you experience distortions during reception of CW, try reducing the RF gain first, then try various levels of attenuator, and combinations of pre-amps, which re-distributes the gain in the front- end.

It worked nicely for me. Signal strengths are irrelevant here; only the undisturbed copy of the desired signal is what counts. I was able to fully copy a CW signal that did not register on the S-meter to begin with, and I was able to still copy it very well with the RF gain setting the S-meter at +20dB over S-9, and 18dB of attenuation engaged. Again the AGC setting was of little to no effect. 

I hope this procedure helps you get clean copy on CW. Oh yes, it also works on SSB as well. 

73 de Matt KK5DR