> That study is on www.yagistress.com
I get "Invalid link" and "not found" for the above so I can not get to their
study or conclusions, but I do have first hand experience with both EHS and
Phillystran of similar ratings for comparrisons.
You are talking very little stretch for Phillistran against almost none for
EHS. So, yes the phillystran has many times the stretch of EHS and it's
still not much. I have not had to retighten my guys since I put them up
(over 3 years) which says a lot. on a heavily loaded 100 foot 45G and I do
mean heavily loaded. http://www.rogerhalstead.com/ham_files/Tower29.htm I'm
working at 100 feet while the top antennas are at 130 feet.
http://www.rogerhalstead.com/ham_files/tower.htm
Do a comparrison, stretch versus the give in the catenary. The give in the
catenary for 130 feet of EHS is many times the stretch and catenary give
added together for Phillystran, at least that has been my first hand
experience.
I'm making the assumption that the phillystran is pre-tensioned before
installation, or at least properly tightened after the Big Grips are in
place.
Something to keep in mind is the natural resonance of the guying system.
While the EHS will tend to be a very low frequency, the Phillistran will be
considerably higher which may or may not be a good thing.
If you are ever "up there" you will note the antennas tend to oscillate back
and forth. This also translates to twisting in the tower. I would expect
to see less twist with Phillystran as there is much less give than with EHS
when stretch and catenary give are taken into consideration. The deep
catenary of the EHS will have a low resonant frequency and depending on the
moment of the antenna system *might* resonate with the swing of the
antennas. Conversely I would expect to see the high natural resonant
frequency and very shallow catenary of the Phyllistran dampen out the
rotation.
I've been up in winds strong enough to bounce me around a bit and I feel no
movement of my 45G, yet I've been up on similar towers guyed with EHS and I
could feel the movement in similar winds.
>From following the thread I agree that there is both a twisting moment and a
hinging/compression moment. I also agree that neither is going to cause a
base failure in a properly rigged tower. Tubing is very strong in linear
compression, so it's most likely to fail where there is the most actual
bending in conjunction with the compression. There is almost no bending at
either the top or bottom of a tower, unless the guys are loose. Torque is
not normally a problem either, but a heavily loaded tower in comparrison to
its rating AND a lot of compression added to the torque of an oscillating
antenna system will greatly increase the stress. This increased stress
comes at a point where the tower is both tending and twisting which reduces
it's ability to maintain the load. It's bending which reduces the
compression strength and it's twisting which further reduces the strength in
pretty much the same area.
Another thing to take into account is the added compression on the base due
to both the tension AND weight of the guys. That is a very good reason to
always use the proper guy and tension and never use over size guy lines.
Having said all this and prefering the Phyllistran for less give than EHS,
I'd most likely go with EHS with a rotating tower. The reason being the EHS
is far less prone to physical damage. It is tough, and has little stretch
with much less catenary give than EHS, but it's just not that tough.
73
Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
www.rogerhalstead.com
>
> 73, Pete
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