Topband: RX antennas

Tom Rauch w8ji at
Mon May 10 09:01:22 EDT 2004

> Quite by accident I discovered that the 40 meter
> was an excellent topband receiving antenna, but only if
> coax running to the 160 meter shunt-feed was shorted-out
> the shack by the BW coax switch which shorted its unused
> inputs (this must have detuned the tower). The
> routinely delivered a 10dB SNR improvement on topband
> signals, and no it wasn't intercept point related.

That's something we should always keep in mind. At some
specific locations, especially when multiple antennas are
packed close together and/or local noise is at work, you can
be surprised at what will work.

Small loops are no exception. (I don't call them "magnetic"
because they are NOT magnetic dominant beyond 1/8th wl. As a
matter of fact, they are electric field dominant at
distances over 1/8 wl up until far field where they are no
different than any other antenna.)

K9AY's and other antennas like flags etc are actually a form
of two phased verticals, and so they have useful (but not
substantial) directivity with a very wide rear null area.
Small loops on the other hand only have two very sharp
nulls. If the noise isn't from a spot direction or you just
don't happen to have a "sweet" location for the loop where
other antennas aid the null, they won't do anything over a
transmitting antenna.

It isn't that small loops won't work in some specific
situations, it's just that in most cases they won't do
anything useful over any other antenna with poor

73 Tom

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