Topband: RX antennas

[Rick Karlquist]

I have found that a 40 meter dipole (@60 ft) is very competitive
with beverages.  I figure this must be because the noise
is mainly vertically polarized.  I would like to try
an array of short dipoles to get horizontally polarized
directivity.  I haven't seen this idea written up anywhere
and am curious if anyone has seen any data on it, pro or con.
I am also wondering about the effect of height.  (Note:
this array would be for receiving ONLY).

Rick N6RK

Tom Rauch said:
>> Quite by accident I discovered that the 40 meter
> inverted-vee
>> was an excellent topband receiving antenna, but only if
> the
>> coax running to the 160 meter shunt-feed was shorted-out
> in
>> the shack by the BW coax switch which shorted its unused
>> inputs (this must have detuned the tower). The
> inverted-vee
>> 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
> directivity.
>
> 73 Tom
>
>
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