Re: [TowerTalk] Shields

["Tower (K8RI)" <tower@rogerhalstead.com>]

VR2BrettGraham wrote:

> <snip>
> 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)
www.rogerhalstead.com


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