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[TowerTalk] 40 meter rotary dipole

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Subject: [TowerTalk] 40 meter rotary dipole
From: (L. B. Cebik)
Date: Tue, 30 Sep 1997 06:47:05 -0400 (EDT)

A rotatable dipole is very useful, and you will get directional--actually
bi-directional--effects so that you can null some QRM to the side.  At 60'
up, which is over 0.4 wl, the pattern will be not a true figure 8, but
more like a peanut with good signal strength reduction off the sides
(dipole ends).  If the antenna is loaded to shorten it, it is unlikely
that the pattern will change and the gain reduction is unlikely to be
noticed.  However, the ability to null signals off the end will come in
handy very often.

I have used many an upper band rotatable dipole for portable and field
work over the years, often hand rotating the antenna (in olden days,
called the Armstrong method).  It often made the difference between a QSO
and lots of futile trying.

A fixed dipole with drooping wires tends to lose some of its side nulls
the more the ends droop toward a true inverted V configuration.  Patterns
tends to oval-ize, with less nulling off the ends.  Hence, if mechanically
feasible, I would encourage use of the new antenna.  But keep the old
dipole for a while, as both an emergency antenna and to make some A-B

Hope these notes help.



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