It is interesting to read of M0BMU's use of a limiter to reduce the
QRM/QRN levels at 9kHz.
I have recently experimented with this sort of technique to improve
my 137kHz QRSS reception. I have added back-to-back diodes on the
isolating transformer between the radio and the sound card. This
helps to reduce the peaks of lightning static and improve
readability.
The best improvement was when I drove the sound card very hard, to
well above the top of the 'volume' bar on the left of Argo (it shows
red all of the time). This completely removed all of the DFC39
'grams' and lightning crashes which previously showed up as bright
vertical lines. It was necessary to reduce the gain of ARGO to almost
minimum.
The background noise was much less 'clean' and Loran lines were a
little fainter, but when testing during the recent Russian evening I
got much better results on weak stations. Strong (audible) stations
showed some distortion, but it was easy to turn the receiver gain
down if necessary.
Mike, G3XDV
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