Hi all,
I'm parallel to Jim M0BMU for regarding that QRSS reception via a sound card
does not benefit from very narrow analogue filtering in the radio, or at
audio prior to application to a sound card. A QRN spike causes ringing and
nonlinearity in a receiver, and effectively subtracts from the remaining
time when the noise to signal ratio is still satisfactory for Argo (or
whatever FFT software) to grind out a useable result. QRN can also cause
AGC hang. The least "outage" resulting from a QRN spike is with other than
very narrow (analogue) bandwidth ...
My QRSS DX receiving setting options are (I use a TS-850SAT):
- IF noise blanker active (clips the spike at a system bandwidth of 16 kHz
or so)
- AGC on fast setting (quickest recovery following a spike)
- IF bandwidth 270 or 500 Hz (and wider could be a tad better still?)
- no outboard audio filtering before the sound card (thus no added ringing).
73, Bob ZL2CA
----- Original Message -----
From: "James Moritz" <[email protected]>
To: <[email protected]>
Sent: Thursday, January 13, 2005 11:45 AM
Subject: Re: LF: Audio Filters
Dear Gary, LF group,
The FFT process of the spectrogram does a very good filtering job, and the
sound card audio input has a surprisingly good dynamic range, being able
to
cope with unwanted signals maybe 70dB or more stronger than the wanted
signal (at least, on the sound cards I have tried, which are nothing
special). The limiting factors usually seem to be distortion in the RX IF
and audio, and audio frequency hash which gets into the sound card from
the
rest of the computer; unfortunately an external audio filter is not much
help with either of these. I find that using a very narrow IF or audio
bandwidth usually worsens the effect of QRN, something in the range 200 -
1000Hz seems best. Where a very narrow bandwidth external audio filter IS
useful is for aural CW reception in the presence of QRM such as carriers
or
other CW signals.
Cheers, Jim Moritz
73 de M0BMU
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