[Lowfer] question about transmitting loop antenna

[Bill Ashlock]

Hi Ted,

Glad to see we have another member of the LF transmitting loop club!  There 
certainly is lot more performance data and experience to draw from, compared 
to about 8 years ago when I wrote two articles on 200ft perimeter loops, in 
which I had to beg others to try them out - particularly in locations that 
had different soil characteristics from my own. At that time I was concerned 
that there was something unique about my soil that made mine have a much 
higher Q, hence higher loop current @ 1w, than others had experienced. 
Turned out that the concern over soil was not warranted but some guys had 
metal towers, metal roofs, and other antennas closeby that did lower 
performance.

>From careful experimentation, and of course using my local soil type, I 
determined that a 200ft loop at 185.3k had to be at least 6ft above ground 
or losses became significant. My later experince up north in the mountains, 
however, indicates that poorer soil conductivity reduces this loss and the 
loop can be closer to the ground. Also, as the loop becomes larger this 
number becomes larger, although I never derived a mathematical expression 
defining this. My sense is that this distance varies in proportion to the 
area of the loop. In other words a loop having half the area can be half 
the distance to the ground for the same loss factor. I also suspect that as 
the frequency goes down the distance can be reduced, but this is likely a Sq 
Root Freq relationship - and results will likely vary with soil 
characteristics.

I hope that once you have a setup that allows you to make accurate 
measurements you will be able to determine the AC resistance of your loop, 
and let us know what it is. Some guys strive for reports of long distance 
reception, but I go for reports of low Rac :)

Good luck and Happy Looping!

Bill Ashlock

----- Original Message ----- 
From: "Ted Holdahl" <ted.holdahl at gmail.com>
To: <lowfer at mailman.qth.net>
Sent: Friday, August 17, 2007 7:04 AM
Subject: [Lowfer] question about transmitting loop antenna


>I am constructing a transmitting loop antenna for use on 137 kHz.  The
> vertical sides of the antenna will be 40 feet and the horizontal  sides 
> will
> be 60 feet.  How close to ground can the bottom of the loop be?  less than 
> 3
> feet above ground would be desirable.
>
> -- 
> Ted
> wd2xyw, kc3ol
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