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Re: LF: loop antenna

To: [email protected]
Subject: Re: LF: loop antenna
From: "John Andrews" <[email protected]>
Date: Tue, 26 Nov 2002 10:57:15 -0500
References: <DDC408CAE72CD511827A0002A5131CD6D9F855@exc_wil08>
Reply-to: [email protected]
Sender: <[email protected]>
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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