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LF: Re: QRSS limiter

To: <[email protected]>
Subject: LF: Re: QRSS limiter
From: "James Moritz" <[email protected]>
Date: Thu, 8 Apr 2010 22:21:25 +0100
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Dear Mike, LF Group,

I have also used this technique on 137kHz, by the crude but reasonably effective method of turning off the AGC on my RA1792 RX and turning the RF gain control to max with AF gain fairly low, resulting in limiting in the IF amplifier. However, on many amateur-type rigs, it isn't really possible to completely disable the AGC in this way, so you will have to provide some external form of limiting as Mike has done.

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.

Limiting seems to "blur" the spectral lines in the waterfall, I presume due to the QRN impulses and other noise effectively randomly modulating the narrow-band signals and so adding a form of noise sidebands to them. But overall, the effect is beneficial under conditions of high QRN, provided no strong signals are present in the RX passband. It would be worth trying the Spectrum Lab limiter (with the RX gain turned back down of course), since this should be more tolerant of the presence of strong signals of varying levels.

Cheers, Jim Moritz
73 de M0BMU



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