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[RFI] Tower/Rotor RFI ?

To: <rfi@contesting.com>
Subject: [RFI] Tower/Rotor RFI ?
From: Larry Kozal" <woowly@home.com (Larry Kozal)
Date: Sat, 18 Nov 2000 17:17:25 -0500
GA, Folks,

Posting this for a contester:

"I have been reading postings here on Towertalk for a year or so &
have not posted anything till now.  This one has me concerned and I
wonder if anyone has experienced a similar problem.

I have two towers, spaced about 125 ft, that run along a 35 degree
bearing line with a 3-stack of 5 el 20M yagis, a 3-stack of 4 el 15M
yagis, and a rotary 80M dipole on one tower and a 40M 3 el yagi and
3-stack of 5 el 10M yagis on the second.

The 20M yagis are mounted on TIC rings and two of the 15M yagis are
mounted using IIX side-arms.  The top 15M yagi and the 80M dipole are
stacked 10 ft apart on the mast at the top of the tower.  Each
antenna in the stack can be positioned independently.  This tower is
130 ft tall, and the 20M yagis are at 37/77/117 ft levels and the 15M
yagis are at 46/87/130 ft levels.  The 80M EF-180C is mounted at 140

The second tower has the 3 el 40M yagi at 140 ft and the 10M yagis
are at 83/50/22 ft levels.  The 40M yagi & the top 10M yagi rotate
independently and the bottom two 10M yagis rotate together on a mast
that runs along side of one of the tower legs.

Here is the problem:  When I aim the 40M yagi at the 20/15/80 meter
tower and key the rig at any power level I experience broadband
(covers the entire 20M and 15M bands) noise.  At 100W, the noise is
tolerable, but at 1500W it is S-9 on both bands, providing the 20M
antennas are pointed at Europe (roughly 45 degrees).  If the antennas
are rotated, no mater where they are pointing, the noise is there.
The noise disappears when the 20M antennas are pointed to Asia or to
the South.

It appears that some form of non-linear conduction is occurring in
the rotation mechanism and generating the RFI.  I have considered
using some sort of conductive grease on the gears of the rings, but
wanted to know if anyone else has experienced this sort of problem &
solved it first.  Additionally, I have no idea where to get
conductive grease at this point in time for the coming contest

Any ideas?  We need help!

>From Larry Kozal   K8PUJ

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