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Some recent comments seem to indicate that all
selectivity should be left to the FFT when using computer derived programs like
ARGO and associated type programmes for narrow frequency modes like QRS.
My approach is to feed the RX audio to the computer
sound card at the narrowest bandwidth possible, in the case of the pegelmessers
at 20 hz b/w. When using conventional receivers with b/widths around 200 hz I
then use an external audio DSP unit and again reduce the bandwidth to the
narrowest possible. Weak signals stand out a lot better when using this method.
On normal cw signals using the most narrow bandwidth possible, commensurate with
speed, makes a big difference to hearing the signal. Signals that are barely
audible with a 300 - 1000 hz filter are perfectly readable with a 20 - 50 hz
filter, the signal over noise is improved dramatically.
The same applies to all modes of signal, minimum
bandwidth to achieve the object.
This is normal commercial practice but some radio
amateurs are still working in the dark.
G3KEV
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