In a message dated 97-01-06 14:03:20 EST, k1vr@juno.com (Fred Hopengarten)
writes:
>>This allows me to disconnect the cables from the boxes within
>>seconds (easy slip in - slip out connectors) anytime I am leaving
>>the operating position or whenever I hear distant rumbles of
>>thunder heralding an approaching storm.
>>
>>The coax is buried in the yard for 250 feet from the hamshack to
>>the tower base, providing a relatively low impedance/resistance
>>path to ground for lightning.
>>
>>Not perfect, but cheap and effective.
>
>K1VR adds:
>
>I too use connectors at the rotators and buried coax (all other lines are
>also buried). So add another vote for these techniques.
>
In order for these aforementioned cables to provide a "low impedance
path to ground", they would have to be CONNECTED to the ground (earth).
Simply burying the cables does nothing to prevent transient damage from
either conducted or induced lightning strikes. That's because they are not
at the same voltage potential as other elements of the ground system (stuck
record, stuck record, etc.).
If you really want your cables to be protected, they should be grounded
at the top of tower where the cable run begins, grounded at the point at
which they leave the tower and turn towards the building and then grounded at
the building entry where your Single Point Ground System bus resides. THEN
you can consider your cables protected. Note: I'm skipping the part about
the rest of the ground system.
Merely disconnecting your cables is a false hope. An average direct
lightning strike won't think twice about jumping from the end of your
disconnected cables to another convenient place that offers a lower
resistance path to ground. It could be the adjacent radio, telephone,
computer, the cable on your TV, etc.
The main thing that you're trying to do is to keep the lightning
transient OUT OF THE HOUSE in the first place. If you do a good job of that,
it really doesn't matter what you do IN the house. By having your cables in
the house unprotected but disconnected, you're still inviting that massive
voltage and current into the house.
Did I mention that I have a "Grounding For Hams" reprint available free
for an SASE? TOWER TECH, Box 572, Woodinville, WA, 98072, is where you can
get it.
73, Steve K7LXC
TOWER TECH -- professional tower supplies and services for amateurs
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