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[Towertalk] Steel vs Phillystran on a Roof Tower

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Subject: [Towertalk] Steel vs Phillystran on a Roof Tower
From: (Jon Ogden)
Date: Tue, 10 Sep 2002 13:33:10 -0500
on 9/10/02 10:08 AM, at wrote:

> You do NOT want any conductors over 12 ft long between
> insulators anywhere near an antenna for 10M.  Note that
> the first insulators must be less than 5 ft from the tower
> to meet this requirement since there is continuity through
> the tower.

That's not quite correct.  If you look in the ARRL handbook, you can find a
lengths of cable that will be fine.  In fact, the ARRL says that 25 feet or
so is about the ideal length.  As you get longer and longer, it gets harder
and harder to get a length of wire that is not resonant on frequency.

> I would use Philystran or some other NON-STRETCH
> non-conductor such as a rope that meets these requirements.

I have used regular steel aircraft wire (purchased from Menards or some
place like that) on my roof tower for the last 5 years.  It has worked great
and is still in excellent shape.

The anchor points in the house roof are green treated 2x4's about 2.5 feet
long that have been lagged into the roof.  I've withstood winds of at least
90 mph with that setup and no problems whatsoever.  N roof tower is a 14.5
foot tripod and until recently had by TA-33, a UHF beam and a 2m Ringo on
it.  The rotor was a Ham IV.  I am in the process of erecting some Rohn 25
for that stuff and the roof tower will hold my satellite antennas from now

> How much guy length could you possibly need on a roof top?
> How cheap do you need it to be?

I had a chat with the sales guy from Phillystran at Datyon this year.  It
was an enlightening conversation.  Kevlar guy wires are not any stronger
than steel.  I had thought you could always use a smaller diameter Kevlar
cable than steel - not true.  For the Kevlar cables, you will need to use
"big grips" and not cable clamps.

The main thing the sales guy told me was that if I was planning an
installation that I would have up for a long, long time - say more than 10
years, then I should seriously consider investing in his product.  But he
said that if I am not necessarily planning on having my setup for that long,
it wouldn't be worth it.  The advantages of Kevlar is that it doesn't rust
and is non-conductive.  It is about 4 times more expensive.

For a roof tower application, there is no reason why you shouldn't be able
to find a wire length that is not resonant at HF and guy your tower with
that length.



Jon Ogden
NA9D (ex: KE9NA)

Life Member: ARRL, NRA
Member:  AMSAT, DXCC

"A life lived in fear is a life half lived."

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