K9YC has done us an amazingly generous service with these publications,
which may be of use to you:
<http://www.audiosystemsgroup.com/RFI-Ham.pdf>
<http://www.audiosystemsgroup.com/CoaxChokesPPT.pdf>
On 7/21/2010 3:00 PM, rfi-request@contesting.com wrote:
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> Today's Topics:
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> 1. Tower Intermod - Control Lines (Ed Richardson)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 21 Jul 2010 06:38:30 -0500
> From: "Ed Richardson"<Ed_richardson@shaw.ca>
> Subject: [RFI] Tower Intermod - Control Lines
> To:<rfi@contesting.com>
> Message-ID:<52C4018D66D14D7F89C796637607445C@radioroom1>
> Content-Type: text/plain; charset="us-ascii"
>
> Installed a 50' Supertitan self support tower a couple years ago. It is
> outfitted with Optibeam Yagis for HF and 6m along with a Foce12 2
> element 40m yagi. I also use quarter wave slopers for 80m and 160. The
> tower foundation is connected to a UFER ground in the foundation as well
> as each tower leg is connected to a ground rod and all 3 rods are
> connected by a ground ring. There are than 3 long radials away from the
> tower as well as a connection to a ring around the house.
>
> The remote antenna switch has 6 positions and when not selected, all
> inputs are grounded.
>
> The problem is that 80m is very noisey and I have AM band
> intermodulation ever 10 kHz from 1.8 to almost 4 MHz. The AM intermod is
> caused by something in the antenna/tower system and is not something
> happening in the receivers. I hear it in the shack when the antennas are
> connected and can receive it on a portable SW receiver when it is
> brought close to the tower.
>
> With a portable SW receiver, I foud that the control lines used for the
> Rotor and remote antenna switch seem to carry this AM intermod and also
> a lot of noise in the lower HF band. Placed a couple chokes on the
> control line (5 turns through five 2.5" ferrites) at the base of the
> tower and it reduced the AM intermod detected around the base of the
> tower. The antennas on top still hear it.
>
> My question(s) - Amyone else experienced this problem? Is there a
> preferred method to shield/choke/bypass the rotor and control lines?
> Should unused antenna ports be left open or grounded? Is tehre a way to
> quiet down this stack of metal?
>
> Thanks for the help and bandwidth.
>
> Ed VE4EAR
>
>
>
>
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> End of RFI Digest, Vol 91, Issue 7
> **********************************
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>
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