Message-ID: <3D53B567.CEBB99A2@snet.net>
Date: Fri, 09 Aug 2002 08:28:23 -0400
From: "Jay Rusgrove" <advancedreceiver@snet.net>
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To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Re: G4JNT and SM6LKM Jason beacons
References: <17chZQ-13Oc8eC@fwd05.sul.t-online.com> <5.1.0.14.0.20020808182124.00b0a1b0@gemini.herts.ac.uk> <005701c23f26$3e24c720$162565d5@oemcomputer> <17cwaH-07Lv5UC@fwd11.sul.t-online.com> <5.1.0.14.2.20020809073006.009f6690@mail.pncl.co.uk> <5.1.0.14.0.20020809115706.00a8a048@gemini.herts.ac.uk>
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Jim

Might be interesting to try an i-f clipper that has well defined
characteristics and is adjustable from "soft" to "hard" clipping. Reminds me of
the early days of SSB rf (really i-f) speech processing.

Jay Rusgrove, W1VD

James Moritz wrote:

> Dear LF Group,
>
> I received G4JNT's Jason beacon again last night, and messed around further
> with the gain levels, etc. I found the best results were achieved with the
> AGC set to manual, the RF gain cranked up to maximum, and the audio gain
> set so that the sound card ADC had a fairly high input level applied, but
> not enough to overload it. Under these conditions, the IF signal was quite
> severely clipped all the time (see the attachment). The audio sounded very
> distorted of course. Backing off the RF gain so that little or no clipping
> occurred made the signal unreadable by Jason, and almost invisible on a
> waterfall display - whilst with the "Jimi Hendrix style" gain settings, the
> waterfall was 'O', and Jason could copy perfectly - the difference was very
> striking and counter-intuitive.
>
> I'm now fairly sure it is not the sound card ADC that is involved in the
> effect, but rather that clipping the signal under QRN conditions improves
> the SNR after further processing. This is the opposite to the optimum
> setting required for receiving QRSS when there are multiple signals in the
> passband; in this case the gain must be reduced until no clipping occurs,
> otherwise "blocking" affects the weaker signals.
>
> I will look out for SM6LKM's 7MHz beacon on the new frequency later today
> when I get a chance.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>
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