[hpsdr] Distortion on AM signals with PowerSDR

[Bob Mahrenholz]

Hi Warren,

I heard you mention on TeamSpeak last Friday, a concern about the distortion on
AM signals with PowerSDR in the AM and SAM modes. While you are looking into
that, would you please see if you can figure our why we get so much 
distortion on
fading amplitude modulated signals (such as WWV) when in the SAM mode.

Synchronous demodulation should eliminate distortion caused by the 
carrier fading.
On broadcast band signals, I have gotten clearer sounding signals by 
selecting the
LSB or USB modes than with SAM. (The receiver is not stable enough to use at
WWV frequencies to use those modes.)

In the past I have built hardware demodulators using a squaring loop 
or a Costas
Loop that did much better than what PowerSDR is doing. If I use a 
long time constant
AGC loop, distortion and amplitude fades are completely eliminated.

Bob Mahrenholz
K4QQK
bobm at edge dot net