Correct Loop Antenna Circumference

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From: James R. Duffey (ji3m@maxwell.com)
Date: Sat Jun 21 1997 - 12:42:02 EDT


Fellow loopers, past loopers, and loopers to be;
With the recent flurry of QRP-L posts on loops I have not seen reference to
the traditional formula for calculating loop circumference giving loops
that are too small. I posted the comments below to the list in response to
a post by Dan Halbert some time ago. The post probably bears repeating as I
have not seen reference to this issue in recent posts. I dug up the
following from my out box;

"I and others who have built loops find that the classical 1005/MHz (in
feet) results in a loop that is too small; that is it is resonant at too
high a frequency. 1033/MHz is a better starting point for loop
circumference although several who have modeled loops have reported values
from 1020/MHz to 1045/MHz result in the correct value for the
circumference. I originally thought that my problems with consistently high
resonant frequencies were due to my use of insulated wire or my poor ground
conducitivity, but NEC models show this effect clearly and others have
noted it as well.

"This was discussed in the NEC list in December 1996 by Belrose, VE2CV, and
Lewallen, W7EL, among others. The postings are available if anyone is
interested, or you can search their archives for them. Belrose said that he
had been trying to get the ARRL to revise its literature which quotes this
figure since the late 70s but had made no inroads in correcting this
classical mistake.

I would bet L. B. has seen this effect."

I got a surprising number of replies to this post, all of whom had seen the
effect in loops they had constructed, but had not seen it pointed out in
the literature. It is truly amazing how long wrong information stays in the
literature.

Keep on looping. - Duffey KK6MC/5

James R Duffey KK6MC/5 DM65
30 Casa Loma Road
Cedar Crest, NM 87008


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