Envelope-to: dave@picks.force9.co.uk Delivery-date: Sun, 12 Jun 2005 14:09:39 +0100 Received: by ptb-mxcore01.plus.net with spam-scanned (PlusNet MXCore v2.00) id 1DhSDa-0006ON-BK for dave@picks.force9.co.uk; Sun, 12 Jun 2005 14:09:39 +0100 Received: from post.thorcom.com ([193.82.116.20]) by ptb-mxcore01.plus.net with esmtp (PlusNet MXCore v2.00) id 1DhSDa-0006N9-77 for dave@picks.force9.co.uk; Sun, 12 Jun 2005 14:09:38 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1DhSCp-000577-9W for rs_out_1@blacksheep.org; Sun, 12 Jun 2005 14:08:51 +0100 Received: from [82.108.183.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1DhSCo-00056y-J5 for rsgb_lf_group@blacksheep.org; Sun, 12 Jun 2005 14:08:50 +0100 Received: from mk-smarthost-4.mail.uk.tiscali.com ([212.74.114.40]) by relay3.thorcom.net with esmtp (Exim 4.51) id 1DhSCl-0003Z4-Qs for rsgb_lf_group@blacksheep.org; Sun, 12 Jun 2005 14:08:50 +0100 Received: from mk-ftp-1.b2b.uk.tiscali.com ([212.74.112.85]:2898) by mk-smarthost-4.mail.uk.tiscali.com with esmtp (Exim 4.30) id 1DhSCg-0002PR-V8 for rsgb_lf_group@blacksheep.org; Sun, 12 Jun 2005 14:08:42 +0100 Received: from [80.225.170.141] (helo=g1l5x3) by mk-ftp-1.b2b.uk.tiscali.com with smtp (Exim 4.24) id 1DhSCe-0002sO-De for rsgb_lf_group@blacksheep.org; Sun, 12 Jun 2005 14:08:41 +0100 Message-ID: <000001c56f4f$3f0c5700$8daae150@g1l5x3> From: "Howard Aspinall" To: rsgb_lf_group@blacksheep.org References: <003f01c56cb1$8567a2e0$0201a8c0@private.network> <000101c56da7$42836300$3daee150@g1l5x3> Date: Sun, 12 Jun 2005 13:27:17 +0100 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 5.00.2615.200 X-MimeOLE: Produced By Microsoft MimeOLE V5.00.2615.200 Subject: LF: Re: Unwanted LF radiation Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Transfer-Encoding: 8bit X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false X-PN-SpamFiltered: by PlusNet MXCore (v2.00) Thanks to all who've taken the trouble to reply. I'm not aware of any water pumping stations in the area, and the LF signal remains when everything is disconnected from the line other than the analyser. DACS boxes are the subject of an interference debate off reflector, but I'm not aware of any round here. I think they are more prevalent in rural areas. The sound is quite unlike LORAN, and I can't imagine LORAN giving me over 5 mV of signal (I hope not!). It seem the LF signal on the BT line bears the hallmarks of broadband. The signal to 130 KHz is over 5 mV into 50 ohms on the analyser. There's the broadband "forbidden" gap showing between 130 and 140 KHz, and the signal above 140 KHz, going into medium wave is weaker, as I'd expect. There's no discernable radiation above 1.1 Mhz. Using Spectran, there are no 50 Hz or 100 Hz bars visible on the signal. I accept what several people have said, that broadband shouldn't cause any problems, but what about a fault condition? Supposing the "A" on a pair feeding broadband has an earth or high capacity to earth. Whilst the broadband and speech facilities would function, wouldn't the corresponding line unbalance increase the crosstalk to other pairs in the same cable? BT say cross talk between pairs is likely and normal but crosstalk giving more than 5 mV common mode signal on my BT line doesn't seem normal to me. The relevant technical standards for the BT system appear to be contained or referred to in a document ND1602:2002/11, downloadable on the Web. It makes good bedtime reading! Incidentally, I gather that the prohibition on connecting non "BT Approved" domestic customer equipment to the BT system has now been scrapped. Apologies for the "broad" bandwidth. Inevitably noise and local interference will continue to affect us all, more and more. I guess these problems would be more managable if amateur radio could acquire "protected" status from Ofcom, rather than "free" licences! Again, many thanks to one and all who responded. Howard G3RXH