[TowerTalk] Water tower omni

[Nick Pair]

Gary,
   
  My assumption was that the coax shield had been grounded prior to conduit which removes the voltage build up due to choke effect of conduit. Bonding at each end of conduit would eliminate current choke effect of conduit.
  Standard practice is to bond shield at point of flexible to heliax connection and again at bottom of tower where coax does a 90 degree turn. This usually puts the conduit on the supply side of the bend, horizontally to the shack.This makes a higher impedance on the branch than the bond drain to the grid and controls the current flow.
   
  Nick
  WB7PEK

Gary Schafer <garyschafer at comcast.net> wrote:
  

> -----Original Message-----
> From: towertalk-bounces at contesting.com [mailto:towertalk-
> bounces at contesting.com] On Behalf Of Nick Pair
> Sent: Monday, July 03, 2006 8:35 PM
> To: ersmar at comcast.net; bthorson at 4smps.com; towertalk at contesting.com;
> n6ry at arrl.net
> Subject: [TowerTalk] Water tower omni
> 
> I vote for the 4 pole folded dipole with the dipoles spaced 90 deg.around
> a mast horizontally and phasing harness distance vertically. The
> commercial type where the dipoles are welded to arm on half opposite feed
> point. They have survived many a strike in commercial installations. You
> would want to use discharge devices above them on support mast and have
> everything well bonded together and to lightning down wire to whatever
> ground is present at tower base. There should be a grid if this is a
> community water system and access to this is important. The individual
> patterns on these are great enough that you get pretty good omni out of a
> set of four. Use factory spacing from support for best omni.
> Also if you can run the feed line horizontally from the support pole
> base through a grounded run of metal conduit just big enough to
> accommodate the coax will choke the large current surge down to a less
> than melt down level. About 20 feet will do it.
> That's my $.02 worth anyway,
> 
> Nick WB7PEK

Running coax through metal conduit without grounding it at each end of the
conduit is asking for a large arc between the coax and conduit, not
recommended.

73
Gary K4FMX




 				
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