[TowerTalk] Ice Bridges

[wowly]

Gents,

My experience is that Andrew Corp. SOP for heliax/coax runs is shield
bonding to tower at antenna end of line, at bottom end (ice bridge height),
and to a grounding plate at building entrance. Grounding kits might also be
seen in the middle areas of the line on 200' plus towers.

Larry Kozal   K8PUJ




-----Original Message-----
From: EUGENE SMAR <SPELUNK.SUENO@prodigy.net>
To: Greg Fox <fox@obsolete.org>; towertalk@contesting.com
<towertalk@contesting.com>
Date: Saturday, July 22, 2000 2:32 AM
Subject: Re: [TowerTalk] Ice Bridges


>
>Greg:
>
>     Read the Polyphaser book, <The Grounds for Lightning and EMP
>Protection.>  In it their engineers recommend bringing ALL coax cables down
>to ground level (both physically and electrically).  Where a commercial
>installation uses an ice bridge to support the coax lines, there exists the
>possibility that the coax shield will be raised to lethal voltages above
>ground at the point it departs from the tower leg.  Bringing the coax to
the
>bottom of the tower and connecting it at this point brings the coax
shield's
>potential very close to that of the buried ground conductors, i.e., much
>less than higher up the tower.
>
>     What I take from reading Polyphaser's book is that all coax cable
>should be bonded to and run away from the tower at or very close to ground
>level where possible.  Most ham installations (except, possibly, for
>repeaters at commercial sites) will be able to follow this design
guideline.
>
>73 de
>Gene Smar  AD3F
>-----Original Message-----
>From: Greg Fox <fox@obsolete.org>
>To: towertalk@contesting.com <towertalk@contesting.com>
>Date: Thursday, July 20, 2000 12:08 PM
>Subject: [TowerTalk] Ice Bridges
>
>
>>
>>
>>Hi there,
>>
>>While working around large broadcast and celluar towers I've noticed
>>one signifigant feature on these towers which the amateur equivelents
>>don't have -- ice bridges.
>>
>>An ice bridge consists of a grating held up by two to three inch steel
>>piping. The purpose is to protect the hardline/waveguide runs from the
>>falling ice which is expected to break off the tower. More or less it
>>creates a "bridge" from the tower to the shelter/cabinets which the
>>lines run underneath of, and are protected.
>>
>>Is this important for an amateur radio installation?
>>
>>In most cases the towers are much smaller, the transmission line isn't
>>in the 1 5/8" - 2" range, and there are not SHP microwave dishes atop.
>>However, I still think it might be a issue with all the alluminum up
>>in the air, due to the nature of HF beams.
>>
>>Any opionons/stories?
>>
>>
>>73s de Greg/KE9R
>>
>>
>>--
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>>
>
>
>--
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>




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