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Re: [TowerTalk] Shields

To: VR2BrettGraham <>
Subject: Re: [TowerTalk] Shields
From: "Tower (K8RI)" <>
Date: Wed, 13 Oct 2004 20:01:32 -0400
List-post: <>

VR2BrettGraham wrote:

With all the energy floating around hilltops, any diode action anywhere is
bound to bring grief. Certainly sounds like the mechanism here & going
to better shielded cable might have simply gotten rid of a bunch of diodes
& not really improved things because of the greater amount of shielding.

Speaking of diode action:
Quite some years back we had the Midland (MI) repeater in my garage. It eventually moved to the basement where the temperature was a bit more stable. <:-))

At any rate, running a tad over 100 watts into the Heliax with the base of the antenna at roughly 90 feet, you could walk up to any of the guy lines near the anchors and completely wipe out a 50 watt mobile 3 to 5 miles away by just sliding a 10" screwdriver up and down the steel guy line.

You couldn't hear the nose on FM, but you sure could on a regular receiver. The repeater would just go deaf. Even flexing the silver plated, double shielded coax at the cans would create substantial noise/desense.

The cans had set without being adjusted for several years. After that long you could hear the bearings during a tune up. <:-)) We used a set of 6 Band pass/band reject (notch) Wycoms. You could get the things within 3 to 6 db by ear with luck, but a spectrum analyzer turned that into a piece of cake. Of course a sweep generator was even nicer. I could always get at least 3 db better with the spectrum analyzer than by ear.
Unfortunately there was a noise problem in the neighborhood that acted like desense. We finally gave up and moved the repeater as we never did find the source.

Roger Halstead (K8RI ARRL Life Member)
Worlds Oldest Debonair (N833R S# CD-2)


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