Return-Path: Received: (qmail 10323 invoked from network); 2 Oct 2002 12:13:36 -0000 Received: from warrior.services.quay.plus.net (212.159.14.227) by mailstore with SMTP; 2 Oct 2002 12:13:36 -0000 Content-Transfer-Encoding: 8bit Received: (qmail 29223 invoked from network); 2 Oct 2002 10:51:04 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from post.thorcom.com (193.82.116.70) by warrior.services.quay.plus.net with SMTP; 2 Oct 2002 10:51:03 -0000 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 X-SQ: A Received: from majordom by post.thorcom.com with local (Exim 4.10) id 17wh4t-0003NI-00 for rsgb_lf_group-outgoing@blacksheep.org; Wed, 02 Oct 2002 11:50:03 +0100 Received: from [147.197.200.9] (helo=hestia.herts.ac.uk) by post.thorcom.com with esmtp (Exim 4.10) id 17wh4t-0003N8-00 for rsgb_lf_group@blacksheep.org; Wed, 02 Oct 2002 11:50:03 +0100 Received: from gemini ([147.197.200.44] helo=gemini.herts.ac.uk) by hestia.herts.ac.uk with esmtp (Exim 3.22 #1) id 17wh3X-0005BN-00 for rsgb_lf_group@blacksheep.org; Wed, 02 Oct 2002 11:48:39 +0100 Received: from [147.197.232.252] (helo=rsch-15.herts.ac.uk) by gemini.herts.ac.uk with esmtp (Exim 3.33 #1) id 17wh3V-0000lF-00 for rsgb_lf_group@blacksheep.org; Wed, 02 Oct 2002 11:48:37 +0100 Message-ID: <5.1.0.14.0.20021002093944.00a8c768@gemini.herts.ac.uk> X-Sender: mj9ar@gemini.herts.ac.uk X-Mailer: QUALCOMM Windows Eudora Version 5.1 Date: Wed, 02 Oct 2002 11:41:29 +0100 To: rsgb_lf_group@blacksheep.org From: "James Moritz" In-reply-to: <000101c269a8$06ba73a0$76717ad5@main> MIME-Version: 1.0 X-MailScanner: No Virus detected Subject: Re: LF: Whoops 137.31 self-inflicted Content-Type: text/plain; charset=us-ascii; format=flowed X-Spam-Status: No, hits=-4.1 required=5.0tests=IN_REP_TO,DEAR_SOMEBODYversion=2.31 Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Dear Alan, LF Group, At 01:09 02/10/2002 +0100, you wrote: > There is something there I have seen for some time >(months) which looks like a very weak 100Hz RTTY shift signal, but this >could be a more distant TV or PC, but this is down at the level of the Loran >sidebands ( which are fairly weak here). > >Cheers de Alan G3NYK >alan.melia@btinternet.com A while ago, I had a problem with a weak FSK signal around 137.4kHz - it turned out to be a 3rd order intermod between the "DCF" stations on 138.83 and 128.93, and DDH47 on 147.3, so: 147.3 - 138.83 + 128.93 = 137.4 The result was FSK, just about audible, with gaps when the data bursts occurred on the DCF signals. The problem was due to the rather wide 1st IF filter in the RA1792 (about 20kHz), in combination with a fairly wide-band antenna - when tuned to 137.4kHz, all 3 signals reach the early IF stages and 2nd mixer with little attenuation, resulting in the intermodulation, allthough they are removed by the main IF filters. The solution was to add preselection with a BW of a few kHz - if the antenna is sharply resonant, this is enough to do the trick. If you are using an antenna that has relatively low Q, there are several possibilities for this type of intermodulation to appear. Cheers, Jim Moritz 73 de M0BMU