Gary Schafer wrote:
>
>> -----Original Message-----
>> From: towertalk-bounces@contesting.com [mailto:towertalk-
>> bounces@contesting.com] On Behalf Of Nick Pair
>> Sent: Monday, July 03, 2006 8:35 PM
>> To: ersmar@comcast.net; bthorson@4smps.com; towertalk@contesting.com;
>> n6ry@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
>
>
>
>
>
Thanks for all the great replies. As far as the immediate need, that
problem is likely solved by a somewhat low tech solution for the time
being, though the problem will arise again in the future, and I'd sure
like to hear more on the subject. The contractor who actually does the
installation work proposed a solution that is somewhat wasteful in the
frequency domain, but is one that I didn't consider in my fascination
with the problem itself. That is, use two different frequencies, one
each for communication with stations on either side of the tower. That
way, we don't have to worry about interaction between the two radiation
patterns and we can mount on the catwalk.
The end cost is probably a bit lower with this solution since we don't
have to spend time tuning and modelling etc. But it would have been more
fun the other way :-(
Ben
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