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[TowerTalk] k90m's rf problem

To: <towertalk@contesting.com>
Subject: [TowerTalk] k90m's rf problem
From: "Jim Jarvis" <jimjarvis@comcast.net>
Reply-to: jimjarvis@ieee.org
Date: Sat, 14 May 2005 05:50:32 -0400
List-post: <mailto:towertalk@contesting.com>
Problem summary:  tribander @ 50' on self-supporting
tower, 3' from house trailer.  Tower grounded w/ 4 gnd rods.
#2 cable runs from that gnd 14' to house electrical panel gnd.

Suggested solution:
(Dick...this expands slightly on my private comments to you...
caffeine kicked in, and I thought of something else.)

1)  Remove the 14' "ground" cable to the electrical power box.
        8' is a quarter wave at 10m, and no longer ground.  16' is
        no longer ground @ 20m.  It's an antenna.  Likely, the whole
        electrical ground system is radiating.
2)  Make sure coax and rotor cables are run along one leg of the
     tower, and exit the base-gnd area at ground level.
3)  Visit Radio Works online, obtain an appropriate grounded line-isolator,
        and install it in the feedline, grounding to the tower base.
4)  While at Radio Works, obtain some # 73 ferrite clip ons...use
        a series of them...6 or more...on the rotor cable, where it
        exits the tower/base/gnd area.
5)  route both coax and rotor cables on-ground to the house entrance.
        consider adding length.  It wouldn't hurt to have 25-50' coiled up,
        on ground.  
6)  You don't mention the entry-system for the cables, but I would
        come in via the shortest possible internal path...up through
        the trailer floor at the shack, if possible. If you could
        install a ground rod directly beneath the shack...reached by
        a 3-4' run of that #2 cable from the equipment...I'd do that, too.  
7)  If you STILL have some RF getting in, add clip ons to both coax
        and rotor cables, where they come into the shack.  

8)  after trying all of the above, only THEN would I attempt to
        tie the trailer frame to the tower gnd system, using a 3 or 4'
        run of #2.  I would expect this to make things worse. Separating 
        the station from the metal trailer is probably the solution. 
        If it has no effect, it probably means the frame and skins have
        no electrical connection.   

Note:  I am not involved with Radio Works, other than as a customer.  
Merely suggesting what has worked for me, in the past.

n2ea
jimjarvis@ieee.org 

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Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions 
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