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From: "Ashlock,William" <William.Ashlock@edwards.boc.com>
To: rsgb_lf_group@blacksheep.org
Date: Tue, 26 Nov 2002 11:17:54 -0500
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Subject: RE: LF: loop antenna
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-----Original Message-----
From: John Andrews [mailto:w1tag@charter.net]
Sent: Tuesday, November 26, 2002 10:57 AM
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: loop antenna


Bill,

> I suggest the transformer approach because when the loop conductor will
have
> some leakage current to the trees (it's small Mal <G>) and this will be
> minimized if the loop is allowed to float relative to ground.

Of course, you could just add a 1:1 transformer on the "50 ohm" side to
float the ground. The 2-capacitor method does have the advantage of
permitting precise impedance transformations. It has the disadvantage of
requiring two vacuum variables at amateur power levels.

> My latest loop experiment is an octagonal TX loop with 3/4" X 10ft sides
> with a calculated Rac of .045 ohms for the conductor alone. Hope to be
able
> to show that the ground loss tapers off to near 0 ohms when it's raised it
> to 50ft. If it doesn't fall off significantly, this may show the reflected
> radiated field absorption in addition to the magnetic field absorption is
> part of the Rac equation. Has anyone performed or know of an experiment
like
> this at LF? If radiation reflection is at work here it may be possible to
> add a ground screen to improve matters.

Last winter, when I ran the "legal loop," I found that laying out several 40
foot strips of chicken wire made no difference on the impedance bridge
readings. That antenna was 15 meters in circumference, done with a cage of
four #8 wires spaced about 10 cm on centers.

John Andrews


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