On Fri, 1 Oct 1999 21:31:05 +0100, you wrote:
Am I missing something? or
am I maybe not sufficiently practiced to take full advantage of the
difference?
Hi
I've been lurking here for a while but am not active on LF (yet). I do make my
living out of EMC measurement and trouble shooting though so have a fair idea of
noise and signal performance,
The theoretical improvements are those that would take place against random
noise, not close spaced strong signals, so if static and atmospheric noise were
the limiting factor then what you say is true.
If on the other hand strong local signals were the problem then nose bandwidth,
skirt shape/depth, and stop band are critical in keeping them out to be able to
hear the ones you want and the improvement because of a reduction in the
adjacent signal can be much greater than the figures mentioned.
When you have spectrogram on the end the actual bandwidth you are looking at the
signal through is that of the FFT process and is MUCH narrower than the receiver
filter.
In this case the rx bandwidth is only a 'roofing filter' and, provided all the
chunk of signal arriving is around the same signal level, the rx bandwidth is
irrelevant. If there are strong signals coming and going within the passband
however this will cause AC pumping and all sorts of problems associated with
that. In this case a narrower bandwidth would help a lot if it kept the
unwanted strong signals out.
Hopefully my understanding of the situation actually ties up with what people
observe on the band, any comments welcome.
Nick
(G4WHO)
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