Return-Path: Received: (qmail 26736 invoked from network); 21 Jan 2000 11:22:37 -0000 Received: from unknown (HELO post.thorcom.com) (212.172.148.70) by teachers.core.plus.net.uk with SMTP; 21 Jan 2000 11:22:37 -0000 Received: from majordom by post.thorcom.com with local (Exim 3.02 #1) id 12Bblg-0003Pt-00 for rsgb_lf_group-outgoing@blacksheep.org; Fri, 21 Jan 2000 10:58:16 +0000 Received: from mserv1c.u-net.net ([195.102.240.33]) by post.thorcom.com with esmtp (Exim 3.02 #1) id 12Bble-0003Po-00 for rsgb_lf_group@blacksheep.org; Fri, 21 Jan 2000 10:58:15 +0000 Received: from rsgb.u-net.com ([195.102.80.225] helo=rsgb.org.uk) by mserv1c.u-net.net with esmtp (Exim 2.10 #35) id 12Bbky-00076i-00 for rsgb_lf_group@blacksheep.org; Fri, 21 Jan 2000 10:57:32 +0000 Received: from miked by rsgb.org.uk with SMTP (MDaemon.v2.8.7.0.R) for ; Fri, 21 Jan 2000 10:41:15 +0000 X-Priority: 3 X-MSMail-Priority: Normal From: "Mike Dennison" To: rsgb_lf_group@blacksheep.org X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106 Date: Fri, 21 Jan 2000 10:41:14 -0000 MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 8bit Subject: LF: Selectivity X-Mailer: Pegasus Mail for Win32 (v3.11) X-MDaemon-Deliver-To: rsgb_lf_group@blacksheep.org X-Return-Path: miked@mail.rsgbhq Message-ID: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group Sender: Interested in the discussions about roofing filters. When I was using a ferrite rod antenna on 73kHz, it had a useful bandwidth of less than 1kHz and needed to be re-tuned for different parts of the band (that's when you could use the whole band - happy days!). This suggests that a few ferrite potted inductors in cascade would provide a front end roofing filter only a few hundred hertz wide at 136kHz. Even easier may be a notch at 138.8 using such a coil. Mike, G3XDV (IO91VT) http://www.dennison.demon.co.uk/activity.htm