Rob Atkinson, K5UJ
k5uj at hotmail.com
Thu May 22 00:41:23 EDT 2003
For most hams it's unrealistic to attempt a professional lightning
protection system. This does not mean nothing should be done--it simply
means there are some things broadcasters can do that most hams are unable to
do because of location, funds and space. Medium wave broadcasters have
towers that are insulated from ground. at the base across the insulator are
johnny balls (spark gap electrodes) so a hit can jump to ground. Most
everyone [on this list] knows the typical mw bc tower is in a field of 120
radials but these aren't 14 gauge wires--one engineer told me they bury
heavy braid to do double duty as dissipaters. 120 1/4 w. radials right
below grade will get rid of a lot of strike energy.
Most broadcast tx sites are unmanned most of the time. Personnel are
therefore insulated from lightning by remote control.
Commercial sites are built from the ground up for communications. Single
point entrances, perimeter grounds, single point grounds etc. are all easy
when you have $$$, are in non-residential zoning, can plow a field, bring in
a backhoe and put down gravel when you are done. Most hams in houses don't
have all these options and disconnecting everything isn't real expensive.
Again, this isn't meant to advocate giving up and doing nothing, it's just
to make the point that these extensive, extremely thorough techniques seem
to come from folks who aren't in touch with every day ham life.
Re the story about lightning coming under a house and back up to smoke the
gear via ground rods, the last time this was told on tower talk, I stupidly
asked if this was a legitimate concern and was told that once lightning is
in the ground, it stays there. duh.
>BC stations have always had to deal with this problem. It's not at all
>practical for them to disconnect, yet they have an outstanding track record
>of being able to stay on the air even when lightning storms are in their
>vicinity. The technology exists, if you are prepared to do it right.
k5uj at hotmail.com
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