Barry Kutner wrote:
> Perhaps a knowledgeable person can answer the following:
> Every time there is a thunderstorm, why don't the commercial stations
> (radio and TV) shut down their xmtrs and unplug their coax?
> Do they do a grounding job so far above and beyond the Polyphaser
> standard (ground rods, bulkhead, surge suppressors, common point
> ground, etc.) that it's OK to stay connected? Or, do they just keep
> replacing equipment as it blows up?
> Bottom line, what does it take to stay connected? How about something
> like a Top Ten box that automatically switches all lines to ground
> when off the air? (is this feasible Dave or George?)
> 73 Barry
> Barry Kutner, W2UP Internet: email@example.com
> Newtown, PA FRC alternate: firstname.lastname@example.org
> FAQ on WWW: http://www.contesting.com/towertalkfaq.html
> Submissions: email@example.com
> Administrative requests: towertalk-REQUEST@contesting.com
> Problems: firstname.lastname@example.org
Finally someone asked the right question.
You keep the lightning outside the station. You don't go off the air.
You don't hide under a tree. You don't play golf in a thunderstorm.
But you have two effective choices. Choose the approach you prefer. You
can prevent the static buildup which allows the strike. There are seveal
companies that sell the equipment and monitors/alarms. Basically they
sell or install a good ground system, and a static dissipation system. It
is typically a spike ball, really a bundle of sharp spikes/wires, bent so
the tips are at different angles, looks like a ball at a distance. When
the static charge between cloud and ground starts to build the corona
from the spikes prevents the charge for rising to a level which would
support a strike. The charged cloud passes over the protected area
without a strike. Chris is absolutely correct that a cone of protection
is provided by providing a high strike point to create a desired spot for
a strike, but preventing a strike may be more desireable. I think the
noise from the corona is unacceptable to a DXer though. There is a
company in Boulder, CO (I've don't remember the name) that manufacturers
the prevention equipment. That have sufficient proof that it works.
I use the cone of protection coupled with bleed off the charge. I have
the 2 in chrome moly mast well above the highest yagi, the mast, tower,
yagis are at DC ground, tower well grounded to several 8 ft ground rods,
#4 solid copper tower to ground system, I have a lightning arrester in
the coax line where the hardline to the top of the tower connects to the
flexible coax to the driven element. Static buildup is shunted to the
tower at the top of the tower. I coil the hardline outside the house. At
the freq of lightning or EMP rise the Xl should be large enough to keep
the pulse going to the ground system not down the coax.
I HAVE been hit by direct lightning strikes MANY times. In Hawaii, New
Hampshire, Colorado that I and family and neighbors have watched. It does
impress the neighbors! One came running over saying "thank you thank you,
you've protected our homes, put it as high as you can." It sounds like a
dynamite blast, the strike hits the top of the mast, the ball of fire
flows down the tower and into the ground. The TV set (in Hawaii) 10 ft
from the tower when from full screen to a dot to full screen. Impresses
Don't disconnect. Keep the strike outside where it belongs.
And Surge Protectors will NOT protect you from a power line strike. Have
insurance. I've been there too.
73 John K1ER
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Administrative requests: towertalk-REQUEST@contesting.com