Darwin, Keith wrote:
When I had narrow filtering in my Omni V I found that S/N did not
increase as bandwidth decreased. Instead, the noise began to sound like
signal since both were at the same frequency. Add some filter ringing
to the mix and sometimes the narrowest settings made copy worse.
It depends on the type of noise. Impulse noise, the kind that noise
blankers work best with, has its duration lengthened by a sharp filter,
which makes it worse. Atmospheric noise, like that caused by
thunderstorms is particularly bad because it contains sharp rise-time
pulses but they are distributed in such a way that noise blankers
generally don't work on it. But many types of noise are reduced
(relative to the signal) by narrowing the bandwidth.
The narrow filter is just another tool in the toolbox that sometimes is
useful. Actually, I have the KAF2, an OHR SCAF, and a Timewave DSP 59+
all hooked up, and under noisy conditions it's interesting to see the
effects of each of them.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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