[Fwd: Q at LF]

Randy Mays randy@pobox.com
Mon, 04 Jan 1999 19:56:37 -0500

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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
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Subject: Q at LF
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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 

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)