Return-Path: Received: (qmail 6879 invoked from network); 28 Apr 2002 07:47:34 -0000 Received: from unknown (HELO murphys-inbound.services.quay.plus.net) (212.159.14.225) by excalibur.plus.net with SMTP; 28 Apr 2002 07:47:34 -0000 Received: (qmail 8917 invoked from network); 28 Apr 2002 07:47:30 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by murphys.services.quay.plus.net with SMTP; 28 Apr 2002 07:47:30 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.33 #2) id 171kgG-0003PC-00 for rsgb_lf_group-outgoing@blacksheep.org; Sun, 28 Apr 2002 10:09:16 +0100 Received: from carbon.btinternet.com ([194.73.73.92]) by post.thorcom.com with esmtp (Exim 3.33 #2) id 171kgF-0003P6-00 for rsgb_lf_group@blacksheep.org; Sun, 28 Apr 2002 10:09:15 +0100 Received: from host213-1-83-46.in-addr.btopenworld.com ([213.1.83.46] helo=dave) by carbon.btinternet.com with smtp (Exim 3.22 #8) id 171j6W-0003pq-00 for rsgb_lf_group@blacksheep.org; Sun, 28 Apr 2002 08:28:16 +0100 Message-ID: <002b01c1ee86$f0a29620$2e5301d5@dave> From: "Dave Sergeant" To: rsgb_lf_group@blacksheep.org References: <002001c1ee43$25ea0dc0$743f01d5@default> Subject: LF: Re: Mains Harmonics ?? Date: Sun, 28 Apr 2002 08:21:23 +0100 MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.50.4522.1200 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: >From Dave G3YMC Thanks for the detailed analysis of TV etc interference to 136. >I see drifty lines with 50Hz and 100Hz spacing, but a quick check at lower >frequencies with teh Rx or SA shows that these are mains modulated signals >with a funamental at 30 to 40kHz and emanate mainly from switch-mode power >supplies, PCs and TVs being the worst offenders. In fact most TV power supplies operate at a switching frequency of around 70kHz, and it is the second harmonic content which appears on 136. You usually also find a strong carrier component at the ninth harmonic of the line frequency (140.625kHz) and as the power supply is often locked to the line timebase this will be modulated with power supply components and is often found to have sidebands spreading over the band (as is the case with my neighbour's wide screen TV). There is not likely to be much 50Hz component with this radiation unless the power supply smoothing cap is faulty. >Another gotcha is that loops dont always help, they will couple magetically >to TV and monitor scan coils at quite large distances (10m+) I had thought my transmit loop was fairly good at not picking up these noise sources, and it is the case in many cases. However my neighbour's tv and its coax feed is quite close to the loop and clearly there is more pick up in that case - the long wire and vertical which are considerably further away pick up much less from that source. Incidentally I still have a page on my website (http://www.dsergeant.btinternet.co.uk/tvqrm.htm) to collate tv qrm problems and indicate the ones to avoid. I have had very little input to this page - if you want a set listed (good or bad) let me know. 73s Dave G3YMC dsergeant@iee.org dsergeant@btinternet.com http://www.dsergeant.btinternet.co.uk