Loop feed, Cebik is correct---

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From: rohre (rohre@arlut.utexas.edu)
Date: Tue Mar 28 1995 - 16:47:18 EST


Bill Acito and all,
Please accept my apology, in trying to help Bill figure out what his observation
of the field Day Loop setup had been, I took his information to imply there had
been a quarter wave of balanced line at the lower band of use. Indeed, a
quarter wave will transform a low to high impedance, but there is a formula for
the optimum impedance of matching section line; and I failed to consider that,
and the fact that a 50 ohm match to the rig or coax implied they would have had
to use the correct impedance line in the match section. (See the Transmission
Lines Chapter of ARRL Handbooks for the formula.)

Thus, given that it was 450 ohm line, one would have to conclude it was only
being used as balanced line and not matched, which is what the clarification
from Bill said he had discovered. My comment of 200 ohms was off the top of the
head for loop feedpoint impedance, and I agree Cebik's program is right on.
These things are variously quoted, and certainly I was correct in saying
external influences can enter in which would be the case if the loop was
unbalanced by the way it is fed. I tend to question the non use of a balun in a
loop feed, for the loop is a balanced antenna, which can function without a
radial system or counterpoise. (However, one local experimenter with SMALL in
terms of wavelength loops, has found by experiment that two spaced loops can
improve the efficiency of the small loop antenna that is tuned by a capacitor
opposite the feed point. He has successfully fed those types with gamma matches
which are not a balanced feed, but again, they were not large loops in terms of
wavelength.)

Anyway, I just wanted to correct my posting with the good points being made by
others. 73, Stuart K5KVH


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