>From: km1h@juno.com (km1h @ juno.com)
To: <topband@contesting.com>
>Date: Sat, 15 Nov 1997 10:05:48 EST
>
>Hi Eric,
>
>I had a somewhat similar tower setup at my old QTH including 3 VHF-UHF
>antennas, a 10-15-20M stack on the mast and another 15M down on a
>sidemount.
>It was not possible to run the 3/4" and 1" CATV hardline down the inside
>so they were all strapped to the outside of the legs.
RF wise, it will work OK as long as the feedline follows the
tower members to the ground. Effeciency and lightning protection
are both enhanced with the proper bonding at both ends and
internal routing. With the lines on the outside of the tower, I
would be tempted to bond more frequently than just at the top
(load end) and at the bottom of the tower. Inside the tower,
there is NO tendency for lightning energy to flash from tower to
feedline through the outer insulation.
Bottom line is that its a good idea to take whatever measures are
necessary to insure that the tower is carrying the vast majority
of RF and lightinig currents. And that the feed and control lines
are at potentials that are not radically different from the
tower.
We routinely run 7/8" hardline up the inside of towers as small
as Rohn 25. It isn't easy but it is worth it to us. Sometimes
the mountains are farther away than the Emperor. For example, we
have had sites in places like New Guinea and Liberia. Both sites
survived lightning OK but not politics. While they were
operational, if there was a fault, it cost us about $7,000 to get
to the site. I doubt that we could get 1 inch or larger line
inside a tower that small without damaging the feedline.
>Control cables for the rotators and relay switching of the 15M stack were
>unshielded and taped to the outside. This was all done a few years before
>I got interested in 160M and built the shunt feed.
>
I didn't mean to imply that no other alternative would work. I
was just recommending what I think is the "best" setup because I
know for sure that has the least potential for problems.
You apparently had a good "cold" ground to work against. That is
the majority of the secret to making towers radiate effeciently.
And it provides the basis for being able to keep the other
conductors out of the act.
73, Eric N7CL
--
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Eric Gustafson N7CL | The mountains are high and
6730 S. Old Spanish Trail | the Emperor is far away.
Tucson, AZ 85747-9498 |
| You can't work 'em
INTERNET: n7cl@mmsi.com | if you can't hear 'em.
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