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[TowerTalk] shack shielding

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Subject: [TowerTalk] shack shielding
From: (Steve Sawyers n0yvy)
Date: Thu, 10 Jul 1997 22:10:05 -0500
Most of the screen rooms that I am familiar with are actually two
separate layers of screen, one inside the other. The outer one is
grounded to earth and the inner one is grounded thru the filtered AC
Ground ie a single point. 

All power and feed lines go through filters. I think the feedline
filters are DC blocked. The door has a double layer of screen also and
it has two continuous strips of finger stock that mesh with two sets of
copper flashing in the door jam and sill to maintain the double
envelope. Even the door latch has an electrically separate inner and
outer shaft with finger stock around the rotating shaft on each side.

I was told by the lab techs that getting one of these to hold 70 dB of
isolation in daily use is a bit of a trick and requires cleaning of the
finger stock on a weekly basis.

I have been very interested in shielding because I am 1300 feet from a
5000 watt AM station at 600KHz. I have a measured filed strength of 1 to
3 Volts per Meter all over the place.

I have three screen rooms stored out in my shed. I got the panels, but
they threw the copper assembly hardware away, so I need a source of
copper wood screws that aren't going to cost me an arm and a leg. I have
checked Granger and McMaster-Carr and had local Fastenal dealer check to
find a source, but could only get offers to have the wood screws custom
turned from bar stock - $$$$!

de n0yvy steve

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