OK1FIG wrote:
We are probably damned to fight agains QRN and QRM. Recently I had
opportunity to buy an external DSP device. I wonder what the experience
of DSP users are. Certainly it is great to have a very narrow non-ringing filter.
I mean rather use of noise-reduction techniques. Do they really provide
a possibility of making very weak signals (normal CW) more readable?
Or is it only a toy and I had better to rely on my well-trained ear?
My experience is that with only one weak signal down in the noise,
an external DSP filter does not give better readability than a "well
trained ear". As the signal gets stronger, or QRM is audible, it is
more comfortable listening to the DSP filtered signal. I have not
found a DSP filter that has an effect on QRN. I think it is worth
having such a filter, if only to reduce the strong close-in QRM that
GW4ALG wrote about (not a problem in OK - yet), but don't expect
to be able to read weaker stations than you can now.
I suspect that the way forward with LF reception is with a very
narrow-band, highly directional rotatable receive antenna with broad
front and steep null. This will allow the reduction of amateur QRM,
electrical noise, and blocking by commercial signals. Interestingly,
when I built an amplified ferrite rod receive antenna for 73kHz it had
a much narrower bandwidth (few hundred Hz) and sharper null than
my 1m loop antenna - but the loop received better!
Mike, G3XDV (IO91VT)
http://www.dennison.demon.co.uk/activity.htm
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