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Hi Mal,
i not agree with your comment, here i have made many test with
narrow band in QRSS, but using or not using an external DSP is exatly the same,
i have aTimewave 599zx, but for qrs no difference.
Also, with narrow bandwidht in IF stage from 2.3 Khz to 250 is
the same when you using the PC and sound card, the only thing is that if we have
an interference in IF bandwidht is better yes the narrow IF filters.(here in
Italy with only 4 active LF station we do not have this problem, hi hi
hi)
Another thing to remember is that with crash like the
tundestorm, the narrow filter make the impulse much more longer than with wide
filter, with DSP filter this situation is not present...., so with crash better
is wide filter and then dsp filter made by FFT PC program.
Another situation in aural CW, the narrower bandwidht the
better is the reception, also in IF and AF with DSP.
Last qso that i have had with M0BMU, was in aural cw but
signal was audible only with 20 Hz DSP filtering and narrow filter in IF
stage!!!
73 to all de IK2DED Giulio
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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