Return-Path: Received: (qmail 12511 invoked from network); 19 Dec 2002 01:44:03 -0000 Received: from netmail02.services.quay.plus.net (212.159.14.221) by mailstore with SMTP; 19 Dec 2002 01:44:03 -0000 Received: (qmail 5987 invoked from network); 19 Dec 2002 01:44:00 -0000 X-Priority: 3 X-MSMail-Priority: Normal Received: from post.thorcom.com (193.82.116.70) by netmail02.services.quay.plus.net with SMTP; 19 Dec 2002 01:44:00 -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 18OpfJ-0004g1-00 for rsgb_lf_group-outgoing@blacksheep.org; Thu, 19 Dec 2002 01:39:57 +0000 Received: from [166.82.1.68] (helo=host3.ctc.net) by post.thorcom.com with esmtp (Exim 4.10) id 18OpfI-0004fs-00 for rsgb_lf_group@blacksheep.org; Thu, 19 Dec 2002 01:39:56 +0000 Received: from att.net ([166.82.181.250]) by host3.ctc.net (InterMail vK.4.03.05.03 201-232-132-103 license 2d687b22c655f23831a2faa19b737467) with ESMTP id <20021219014043.JKWS28227.host3@att.net> for ; Wed, 18 Dec 2002 20:40:43 -0500 Message-ID: <3E01237A.8873C993@att.net> Date: Thu, 19 Dec 2002 01:40:10 +0000 From: "Dexter McIntyre W4DEX" X-Mailer: Mozilla 4.77 [en] (Win98; U) X-Accept-Language: en MIME-Version: 1.0 To: rsgb_lf_group@blacksheep.org References: Subject: Re: LF: Big vs small RX antennas Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 8bit X-Spam-Status: No, hits=0.4 required=5.0tests=CTYPE_JUST_HTML,REFERENCES,SPAM_PHRASE_00_01, USER_AGENT_MOZILLA_XM,X_ACCEPT_LANGversion=2.42 Sender: Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group The first 136 kHz US receptions of G3AQC and MØBMU made nearly two years ago were made with my 160 meter dipole. The dipole is supported with a 1 meter side arm from the 95 foot level of a 100 foot, insulated guy wire tower. The home brew open wire feed line was fed as a single wire with a series pot core inductor to bring the antenna to resonance. Later test were made comparing the TA signals received with this antenna to a 3.3 square resonant loop. This loop was matched with a single turn pick up loop. The two antennas were comparable for 136 kHz reception most of the time.

Last year I constructed a new receive loop, octagon in shape, twenty turns, a little over 3.3 meters diameter. This loop is center tapped and feeds a balanced preamp. Every comparison I made showed this balanced fed loop to outperform either the old loop or the T vertical wire. I'm a firm believer in the balanced loop design.

W4DEX
www.w4dex.com

MarkusVester@aol.com wrote:

Hi John and LF group,

Just curious -- since the signal to noise ratio in my receiving installation
appears to be limited by external (man-made and atmospheric) noise, rather
than noise in my preamp/receiver, how would a 100 foot tower improve that
situation?
John Andrews, W1TAG

A big vertical does help a lot against local noise-sources (neighbours' TVs and SMPSs), but with anything originating further away than a couple of 100m, it makes absolutely no difference.
However the directivity provided by a magnetic receive loop can be valuable. If all of the noise was coming in isotropically from the horizon, the figure-eight pattern would theoretically have 3dB better SNR than a vertical, and a cardioid combination would gain 4.8dB. In practice, of course one can often null out a source of QRM or a thunderstorm front and have far greater improvement.
The only problem I am having with small loops is that they seem to be much more prone to local pickup than the E-field antenna - at least in my suburban area which has underground mains wiring. The 86cm-diameter pair in the garden is often swamped by notorious 100Hz-modulated carriers which at the same time I can hardly see on the marconi.
73 de
Markus, DF6NM