Hi Brian,
I don't think you are asking for trouble per se. But you are
asking for a requirement that you exercise somewhat more care in
the design of the ground system.
Only you know what the value and vulnerability of the stuff in
and around the barn is likely to be. If it is an abandoned
facility which is unlikely to have animals or personnel in or
near it during a storm, that is one set of circumstances. If it
is an active dairy operation which is likely to have people and
livestock working in the vicinity and valuable production
equipment in operation, that is another.
The "rule of thumb is ok if no lightning protection effort can be
tolerated. But it doesn't mean that a tower cannot be safely
located adjacent to a tall conductive antenna structure.
Buildings located next to towers are routinely lightning
protected to the degree that the radio station inside the
building can and does operate right through a direct hit on the
antenna structure without any damage to the building, equipment,
or personnel in the vicinity or even any interruption in service.
There is an FM transmitter south of town here (Tucson, AZ) that
gets hit an average of twice a day during our monsoon season.
Probably, the safest possible place in the entire valley for a
person to be during a summer thunderstorm here is inside that
transmitter building. It is all a matter of how much attention
is paid to the lightning protection system requirements.
Start with the PolyPhaser book "Grounds for Lightning and EMP
Protection". And get a (free) copy of MIL-HDBK-419A Vols. I and
II. This is by far the best reference on this subject I have
ever seen. It has both the theoretical basis and practical
instruction relating to lightning protection. Do some reading.
Don't stop until you understand the concept of "step potential"
and how to control its magnitude. Then decide on where you want
your tower based on the ground system effort required for your
situation and what you are willing or financially able to do.
73, Eric N7CL
>From: "Brian Smithson" <brian_smithson@vds.com>
To: <towertalk@contesting.com>
>Date: Mon, 11 Oct 1999 09:54:34 -0400
>
>Uh oh,
>
>> Regarding tower placement, the rule of thumb is a minimum of
>> 50 feet away from the nearest person or structure. A tower
>> will tend to attract lightning, so you don't want to attract
>> it right near your home
>
>I've marked out a spot for the base of my 2nd Trylon
>self-supporting to be close to a barn in our backyard. The barn
>is >300' from the house, but the tower will (was going to) be
>less than 10' from the barn. I'm planning a pretty extensive
>ground system - am I still asking for trouble?
>
>-Brian n8wrl
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