At 09:06 PM 8/30/03 -0400, Tom Rauch wrote:
The most benign place is the middle of the tower, where a Faraday cage is
formed by the structure itself. That's where the sensitive cables should be
routed, and they should be inside shields or metal conduits bonded to the
tower at tower exit points. Feedlines should at least be grounded to the
tower at the top and bottom, or better yet inside the "cage" and grounded
where they enter and exit.
I'm not sure what you're saying here, Tom -- do you mean this is the place
where there is least likely to be voltage induced in the cables? In my
case, all coax and control cables run inside the tower until they reach
ground level, wherever they enter it -- two coax and one rotator at the
top, one control at 84 feet, and one coax and one rotator at 69 feet. The
antenna relay switchbox is at the bottom.
I have been remiss in not grounding the shields of the coax top and bottom,
and of course I don't have that luxury with Romex or twisted-pair control
cables. Rigging metallic conduits or shields around all control cabling
would be prohibitive. It now looks as if one rotator motor winding may be
OK, but both rotator position pots are shot for sure, and there are no
relay coils evident from the shack end of the control cables for the
Stackmatch and antenna switch. I think the only viable approach is
probably to replace everything but the antennas on the tower, do the coax
shield grounding next time, and regard a certain level of losses of
ancillary on-tower equipment as a cost of doing business when lightning's
around.
73, Pete N4ZR
The World HF Contest Station Database was updated August 30.
129 stations were added or updated.
Are you current? www.pvrc.org/wcsd/wcsdsearch.htm
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