Return-Path: Received: from rly-md08.mx.aol.com (rly-md08.mail.aol.com [172.20.29.146]) by air-md02.mail.aol.com (v124.15) with ESMTP id MAILINMD023-91d4a8d7426330; Thu, 20 Aug 2009 12:05:32 -0400 Received: from post.thorcom.com (post.thorcom.com [193.82.116.20]) by rly-md08.mx.aol.com (v124.15) with ESMTP id MAILRELAYINMD085-91d4a8d7426330; Thu, 20 Aug 2009 12:04:57 -0400 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1MeA6q-0007vy-2O for rs_out_1@blacksheep.org; Thu, 20 Aug 2009 17:03:28 +0100 Received: from [83.244.159.144] (helo=relay3.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1MeA6o-0007vp-Uz for rsgb_lf_group@blacksheep.org; Thu, 20 Aug 2009 17:03:27 +0100 Received: from smtp-vbr10.xs4all.nl ([194.109.24.30]) by relay3.thorcom.net with esmtp (Exim 4.63) (envelope-from ) id 1MeA6i-0004nV-GV for rsgb_lf_group@blacksheep.org; Thu, 20 Aug 2009 17:03:22 +0100 Received: from webmail.xs4all.nl (dovemail11.xs4all.nl [194.109.26.13]) by smtp-vbr10.xs4all.nl (8.13.8/8.13.8) with ESMTP id n7KG3Ax0013219 for ; Thu, 20 Aug 2009 18:03:20 +0200 (CEST) (envelope-from roelof@ndb.demon.nl) Received: from 82.161.81.65 (SquirrelMail authenticated user pa0rdt) by webmail.xs4all.nl with HTTP; Thu, 20 Aug 2009 18:03:19 +0200 Message-ID: In-Reply-To: <20090820150437.322210@gmx.net> References: , <4D0A429582694836812C0FB6FDCADEDD@mjusamsung>, <20090820141918.53610@gmx.net> <4A8D626A.10122.200EDD0@dave.davesergeant.com> <20090820150437.322210@gmx.net> Date: Thu, 20 Aug 2009 18:03:19 +0200 From: "Roelof Bakker" To: rsgb_lf_group@blacksheep.org User-Agent: SquirrelMail/1.4.18 MIME-Version: 1.0 X-Virus-Scanned: by XS4ALL Virus Scanner X-Spam-Score: 0.0 (/) X-Spam-Report: autolearn=disabled,none Subject: Re: LF: Re: Tree noise Content-Type: text/plain;charset=iso-8859-1 Content-Transfer-Encoding: 8bit X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=none autolearn=no version=2.63 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-AOL-IP: 193.82.116.20 X-Mailer: Unknown (No Version) Hello Dennis, Though vertical antennas (and active whips) have a bad name in regard to local noise, this is not necessarily true for reception at LF. Local noise in the electric field is attenuated by the walls of the building (except for a wooden one), whilst the magnetic field of a local noise source is not attenuated at all. I have measured 30 - 40 dB of electric field attenuation at 400 kHz. The bad name of verticals in regard to local noise is not in the antenna itself, but due to bad engineering practices in the feedline system. So called common mode noise travels along on the shield of the feedline from inside the house towards the outside world and is received on the antenna. A few simple precautions can solve this problem: use a rf-isolating transformer between the feedline and the receiver and/or connect the shield of the feedline at the bottom of the mast to a groundstake. I have also used a couple of twisted pairs of a CAT5 network cable to feed DC and RF separately to an active whip with excellent results. The balanced twisted pairs offer some 40 dB attenuation against noise ingress. Loops are excellent reception antennas. However in my location they are quite useless, whilst I have stellar low noise reception using an active whip. (I have logged a NAVTEX message from Taiwan on 518 kHz). Best regards, Roelof Bakker, pa0rdt