[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: US Towers



>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

Jon, all:

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
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!

----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home