[TowerTalk] Station Ground

[Pete Smith]

Just a sidelight on this.  As a legacy of the past, I have a bus-bar system 
connected to my single point ground bulkhead, but alas, the distance to 
actual ground from my second floor window is several meters and the ground 
lead cannot be straight.  Despite my use of copper tubing for the bus bar 
and heavy copper ground leads from every piece of equipment, I found that 
when I tried to use my sound card for contest "voice keying" I had fairly 
severe AC hum on the audio, apparently the result of a few millivolts 
potential difference between chassis.  I finally cured it by experimentally 
connecting the chassis of the computer and radios directly to one another 
with heavy copper (not through the bus bar).

As for lightning, given my technical limitiations, I am very uncertain 
about getting the chassis of all the equipment to rise and fall together 
during a strike.  I have opted for disconnecting all conductors from the 
tower to the shack at the window bulkhead instead.  During a direct hit on 
the tower in 2003, the only units damaged in the house were computers 
connected to a CAT-5 network cable running downstairs (~75 feet long) -- 
everything on the tower itself, 200 feet away, was fried.

73, Pete N4ZR

At 11:19 PM 1/14/2005, Ward Silver wrote:

>One thing has been overlooked in the discussion of grounding with respect 
>to lightning and ac safety.  I don't disagree with anything W3LPL had to 
>say, but I would like to point out that it is important to keep all of the 
>equipment close to the same RF potential as possible.  This prevents RF 
>feedback and circulating current between pieces of equipment.  Connecting 
>all of the equipment together with a low-impedance strap is a good way to 
>accomplish this.
>
>Note that you probably can't make that RF potential equal to zero because 
>of the length of the connection between the strap and earth.  That doesn't 
>matter, you just want the radio, the tuner, the audio mixer, whatever, to 
>be at the SAME potential to prevent current flow between their 
>chassis.  This is a particular problem with "second story" shacks where a 
>connection to true ground may be meters long.  At multi-position stations, 
>it's also impossible to keep all the equipment at the same potential and 
>so you have to settle for keeping the equipment at each position at the 
>same potential, even though that may be many volts different than one of 
>the other positions.
>
>73, Ward N0AX
>
>_______________________________________________
>
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>Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with 
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>
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