[TowerTalk] Rotating a dipole on a side-arm

Gene Smar ersmar at verizon.net
Tue Nov 24 19:35:50 PST 2009


Scott:

     I have a Cushcraft D40 (compact) rotatable dipole at the top of my 
tower's mast at 78 feet.  I find that it is pretty much non-directional, 
that is, I can't seem to find a null or even a measureable drop in RX levels 
when I rotate it.

     My point being is that on 40 and probably 60 meters, the SteppIR dipole 
will probably not have to be rotated at all.  If you intend to operate on 
the higher freqs during an emergency, then you might see some directionality 
that will have to be overcome by turning the antenna.  But under what 
circumstances would you be using freqs above 7.3 MHz during an EOC 
activation?  The EOC's mission should have a major influence on your choice 
of frequencies and hence antennas.


73 de
Gene Smar  AD3F


----- Original Message ----- 
From: "Scott Honaker" <scotthon at pilchuckvet.com>
To: <towertalk at contesting.com>
Sent: Tuesday, November 24, 2009 6:15 PM
Subject: [TowerTalk] Rotating a dipole on a side-arm


>
> Our county is building a new Emergency Operations Center and tower.  We
> have had notoriously bad luck with our roof-mounted wire HF antennas.  I
> have been considering using an HF multiband dipole (like a SteppIR) on the
> tower.  There will be a microwave video downlink at the top so I am left
> with a side-arm mount.  I see the Tessco catalog lists 72" side-arms.
>
> The next question is how to I rotate it and not whack the tower.  I need a
> rotor or controller with adjustable stops.  Does such a thing exist?  I
> can't trust simply marking the display with a "don't turn here sign".  The
> rotor needs to not go there.
>
> We expect to use a free-standing 3-legged tower so I anticipate I can get
> at least 90 degrees of rotation.  That should let me cover any bearing and
> hopefully let me reduce the effect of local noise.
>
> What should I be considering?
>
> Thanks,
>
> Scott N7SS
>
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