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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