Topband: Magnetic loops

[D. S. Coleman]

All:

I can comment on my experiences with a magnetic loop, as I have one,
along with three one-wavelength beverages, and a pennant terminated
loop.  Each of those antennas, at one time or another, proves its
worth as a receiving antenna at my station.  In terms of signal to
noise ratio, the Beverages win most of the time, but not always.

Sometimes the terminated loop wins, especially if there is a storm
front off the back null.  The low angle lobe and rearward null is a
big advantage for the terminated loops.  The pennant has about the
same RDF as the K9AY and the latter is switchable and you can get four
directions in a small space.  There is a lot to like about terminated
loops.

There are also times when the magnetic loop wins, although it should
not, since is has a very low RDF and sees the entire sky dome and has
only its two deep nulls that are I have oriented toward some noisy
power lines.  The loop is a little over 6' in diameter and made from
75-Ohm 5/8" hardline, with a +20-dB preamp built into its interface.
The loop is about 400' from the house and is in a fairly quet location
and fed with flooded RG-6.  It gets the most use as a general
listening antenna on 160M, until the beverages are brought online in
the hunt.  Sometimes though, the magnetic loop really does hear better
than any of the others, even though it should not.  I am wondering if
it is because it does receive the entire sky dome and sometimes hears
a high angle signal that may otherwise be down in a nulls of one of
the other antennas, or maybe its physical isolation and its nulls
toward that old noisy power lines that carries the day.  Or maybe it's
because it is very narrow banded and does not deliver nearly so much
broadband energy into the receiver.  I don't know for sure why it is,
but more times than I can count I have been thankful that the magnetic
loop is on the RX switch.  It earns its keep.

On Topband, ANY receiving antenna is better than listening on your
transmit antenna and you can never have too many receive antennas.
Magnetic loops are a good place to start, as they are small, cheap,
will fit nearly anywhere and are easy to make.  Terminated loops are a
big improvement in directivity, but have a larger footprint.  Beverage
antennas are in a class by themselves and generally beats everything
else--except when they don't.  It happens.  You can never have enough
receiving antennas and it's surprising what works the best sometimes.
Just keep turning that RX switch.

73,
Steve
AB4I

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> This is a great topic as there are a lot of us on small lots active on
> topband needing what ever edge we can find.......
>
> Do you have this loop you've designed published where we can see it?  I know
> as a low power backyard set up with a MA160V, it would be interesting to
> look into.....we have an East/West oriented K9AY that has got back on 160M
> with an awesome receive.  It would be fun to play around with a loop but not
> sure which one to decide on- We still need 24 for DXCC on topband and we
> need every bit of help we can get!
>
> 73!
>
> Paul  N0AH
> Anna W0ANT
> Peggy KD0ISN
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