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40 meter rotary dipole

(Dennis Schaefer)875587822Tue, 30 Sep 1997 02:50:22 +0000 (UTC)
I have always used wire antennas and verticals on 40 meters with good
success.  I recently acquired a KLM 40M-1 "dipole module".  This is
essentially a 47 foot single element antenna which is intended to be placed
above another HF beam.  I've never used anything like this before.

I only bought it because the price was irresistible, but now I'm thinking I
might want to use it above my KT-34XA.  I know it should be mounted in line
with the XA's boom.  

 Will I get better DX performance with this antenna at about 60 ft. than a
full size dipole  at about 50 feet (which generally ends up with the ends
drooping down to 30-35 feet)?  Will I notice the directive effects as I
rotate this antenna?

I have lots of 50-55 foot pine trees to hang wires in, but this antenna
seems like it might work.  On the other hand, my XA will load the 25G/Hazer
and Ham IV rotator pretty well, so had only planned to top it with a
2-meter beam.   (This isn't much bigger than a 2M beam - just 2 sq ft. )

What do you think?  Send to me and I'll summarize for the group.
Thanks, 73,
L. B. Cebik @b.>875616425Tue, 30 Sep 1997 10:47:05 +0000 (UTC)

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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