[Fwd: Q at LF]

[Randy Mays]

This is a multi-part message in MIME format.
--------------DC5395D3C847BD7C3102E6A2
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit



--------------DC5395D3C847BD7C3102E6A2
Content-Type: message/rfc822
Content-Disposition: inline

Received: from chai.pobox.com (chai.pobox.com [208.210.124.35]) by ns2.win.net (8.8.8/8.6.9) with ESMTP id GAA14327 for <ramays@amrad.win.net>; Mon, 4 Jan 1999 06:03:03 -0500 (EST)
Received: from atanasoff.amrad.org (atanasoff.rf.org [204.29.138.196])
	by chai.pobox.com (VMailer) with ESMTP
	id 5CF4A15FF; Mon,  4 Jan 1999 06:00:49 -0500 (EST)
Received: from mserv1a.u-net.net (mserv1a.u-net.net [195.102.240.34])
	by atanasoff.amrad.org (8.9.1a/8.9.1/Debian/GNU) with SMTP id FAA20490
	for <editor@amrad.org>; Mon, 4 Jan 1999 05:00:44 -0600
Received: from rsgb.u-net.com (rsgb.org.uk) [195.102.80.225] 
	by mserv1a.u-net.net with smtp (Exim 1.82 #2)
	id 0zx7kf-0007YJ-00; Mon, 4 Jan 1999 11:00:50 +0000
Received: from miked.rsgbhq [192.168.2.30] by rsgb.org.uk [192.168.2.132] with SMTP (MDaemon.v2.7.SP3.R) for <editor@amrad.org>; Mon, 04 Jan 1999 10:56:39 +0000
From: "Mike Dennison" <mike.dennison@rsgb.org.uk>
Organization: Radio Society of Great Britain
To: editor@amrad.org
Date: Mon, 4 Jan 1999 11:00:38 -0000
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Subject: Q at LF
Reply-To: publications@rsgb.org.uk
Priority: normal
X-mailer: Pegasus Mail for Win32 (v3.01d)
X-MDaemon-Deliver-To: editor@amrad.org
Message-Id: <E0zx7kf-0007YJ-00@mserv1a.u-net.net>
X-Mozilla-Status2: 00000000
Content-Transfer-Encoding: 7BIT


I read the article by Hal, WB3KDU, (vol XXV no2) with interest. 
However, I note he makes a mistake often seen in articles about 
LF. He supposes that the antenna Q will be extremely high, 
quoting commercial experience and theory. Certainly, a practical 
amateur LF antenna will have a small bandwidth but this is not the 
fractions of a Hertz often seen in theoretical articles. It is not even 
several Hertz. A good practical antenna will have a 3dB bandwidth 
of a few hundred Hertz, whilst an effective antenna might be 1kHz 
wide. 

Why? Losses, mainly resistance! In the case of a loop, wire 
resistance is important. A practical LF loop must have wire thin 
enough to support (and cheap enough to buy), and N4ICK's 0.8 
ohms is good. In the Marconi case a practical earth will have 
several ohms (often many tens of ohms) resistance. But there are 
other losses. Ironically some of these will be in the very matching 
systems which WB3KDU is aiming to replace.

Whilst a low-loss system is important for efficiency, do not assume 
that all losses are bad news - most contribute to the necessary 
bandwidth of the antenna.

73 to all US LF enthusiasts.



Mike, G3XDV (IO91VT)
http://www.dennison.demon.co.uk/activity.htm



--------------DC5395D3C847BD7C3102E6A2--