Topband: Fw: 25G insulators

[Pete Smith]

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
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