Re: [amsat-bb] US Towers

["Dr. Jim Akers" <jakers@xxxxxxxxxxxxxxx>]

Dr. Jim Akers
Dept. of Electrical 
and Computer Engineering
Miss. State Univ. 


On Mon, 22 Oct 2001, Edward R. Cole wrote:

> >Be VERY careful with crank up towers and wind loads.  All of the US Towers
> >models are rated at 50 MPH winds.  An 18 to 24 sq foot load at 50 MPH is cut
> >about in half at 70 MPH.  So at 70 MPH, it will only handle around 9 to 12
> >sq feet.  If you have higher winds that that, be ware.
> >
> >I know this because I have just gone through deciding on whether or not to
> >purchase a crank up tower from a ham I know.  We sometimes have 90 MPH wind
> >gusts here and I decided it was just not safe.
> >
> >Your winds may be lower.  I think you can usually get wind profiles from
> >county offices, weather service, etc.
> >
> >Fortunately, VHF/UHF and Microwave equipment has less wind loading than HF
> >antennas (OK, big arrays excluded).  Keep in mind also, that if you live in
> >an area where you have ice storms that you increase wind load as well.  BBQ
> >dishes have a lot of surface area for ice to attach to.
> >
> >For more information on crank-up towers, look at the Tower-Talk archives on
> >www.contesting.com or join the Tower-Talk reflector.
> >
> >73,
> >
> >Jon
> >NA9D
> 
...snip...
 
I have a 72 ft. US Tower crank-up.  I leave it "hunkered down" most of the
time unless I anticipate HF ops.  It recently withstood 95-100 mile/hr
winds with a large KLM tribander, a 2m yagi and a Diamond 500 on the top.
It was at the 21 ft. level.  Lots of trees in the area went.  Some that
were many years old.

...snip...

> Good points to ponder.  I use a 40-foot Rohn-25 tower to support my 2m-eme
> array of four 21-foot crossed yagis with wind area of 16-18 sq. ft.  I
> decided to use a Hazer lift system to enable me to work on the equipment at
> any time by lowering it to ground level [reachable from a 10-foot step
> ladder].  Also, if high winds are predicted, I can lower the array to avoid
> the tower loading as well.
> 
> A sidenote:  Winter has arrived up here and we have 20-inches of snow on
> the ground...and on the AO-40 antennas.  I went up on my {flat} roof and

Man, I hate it when that happens.  It is 81 degrees here in Mississippi:-)

> removed the snow from the antennas and dish feed yesterday.  I removed the
> snow from my ku-band TV dish also since my reception totally went away with
> snow covering the feedhorn!  I leave the AO-40 dish at a low elevation
> {zero-20 deg} stowing position facing south to catch noon sun.  Little snow
> accumulated on back side of the dish in this position.  Since the dish is
> offset fed, it points downward below 23 deg elevation and snow cannot
> accumulate on the dish face.
> 
> Well anyway I put the lawnmower away and got out the snowblower ;-)
> 
> Ed
> PS:  bought a new rover machine Saturday - 2002 Toyota Tundra pickup!

Sounds like you may need it!!

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73...Jim...W5VZF.

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