Topband: DSP and Digital Filter Effectiveness for

[Tom Rauch]

> Just wanted to echo Bill's AGC comment.  I put a couple of
> back-to-back diodes in the headphone line as an ear saver and go
> AGC-less during bursty static with the 1000MP.  Even the fast AGC
> release time is too slow in these condx to maintain copy of a weak
> signal under static bursts.

The wide filter or a wider filter works best with the 1000D and all 
of my other receivers.

The reason a DSP system works poorly on the audio line is the DSP 
system looks at wave shape. Noise normally has a very high peak and 
short duration. But if the noise has gone through several stages with 
significant selectivity, it can't do anything with the resulting 
signal. That's because the noise appears almost like a good signal, 
when you look at small slices of the waveform.

The DSP system can work like an audio filter, and sort the tones out, 
but it can not eliminate or reduce lightning crash noise if there is 
any selectivity ahead of the DSP system.

I do have receivers with very fast very good AGC systems, and they 
work very well during static crashes with AGC on, but I still find 
that wider selectivity helps.

Wider selectivity helps because the sharp waveform of the static 
crash is not lengthened and blurred, and so my ears can do a better 
job of filtering the noise from the signal.

The best DSP system in the world for copying weak CW in noise is our 
brains, if conditioned to do that.73, Tom W8JI
W8JI@contesting.com