From: WarmSpgs@aol.com
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Date: Tue, 8 Jan 2002 16:08:53 EST
Subject: Re: LF: Receiving loop very close to the ground
To: rsgb_lf_group@blacksheep.org
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>I know that I can illuminate(to some extent) a light bulb by connecting it
>to the hot side of the mains and grounding it to the earth indicating that
>there can be significant current flow in the earth at 50/60 Hz.
>
>1) Can there also be significant flow at harmonic frequencies of the 50/60
>Hz?  If so does this mean that an antenna low to the ground like mine,
could
>be picking up some of that energy that may be in the LF bands?
>Would raising it to 5 feet help eliminate some of that noise?
>
>2) Does raising a loop have any effect on the received signal strength
other
>moving the antennas resonance point?
>
>3) Is it possible to shield one side of a loop antenna  with say wire
>fencing a few feet away to  elimiinate noise coming from 1 direction and
>thus making the unidirectional instead of bi-directional.
>
>After all are not we playing the game of signal against noise.  To extend
>the range of a given station should much consideration be given to
>minimizing the undesirable noise, either man-made or natural ?   Isn;t the
>noise the limiting factor here?
>
>Please tell me if I am all wet...  I will go get a towel
>


A dry washcloth should suffice, Paul.

You surmise correctly on your first question.  Earth currents can induce
noise into a loop.  Sometimes there's not too much effect, sometimes quite a
bit.  Moreover, the proximity of the partially-conducting earth affects such
things as the depth of null you can obtain with the loop.

Second question:  Yes, height of the loop can make a difference in signal
strength.  It's not a linear relationship, but a bit of height may either
get you away from sources of noise, or improve signal strength, or both.

Third question, though:  It is not effective to "shield" a loop in the
manner you describe.  Currents in the fence will couple either signal or
noise--or both--into the loop, and also adversely affect its directional
properties.  It could eliminate your ability to achieve nulls in crucial
directions.

There are other ways, though, to utilize a loop in a unidirectional
configuration rather than bidirectional.  If you combine the output of a
loop with the output of a whip, with provision for matching the signal
levels of the two antennas, you can achieve quite a nice cardioid pattern in
situations where that would be more useful than the two nulls of a
figure-eight.  To learn more about steerable nulls and phasing and matching
of two antennas, I recommend visiting www.lwca.org and scrolling down to the
lower half of the home page.  Click the link for "On The Art of NDB DXing,"
and go to Chapters 4 and 5 for some very useful ideas.

73,
John Davis