Topband: RX antennas
w8ji at contesting.com
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
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
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