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RE: Antenna Dish

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THANKS so much for all the input.  This helps me to remember why we have
this list, and how valuable it is to me.  I am currently working on getting
a copy of the ANSI/TIA/EIA-222-F-96 standard, which I THINK I can get
electronically from Global Engineering something or other (thanks James
Cohen from NJ). I think that will give me the insight I need, although many
if not all of the suggestions/opinions furnished by listserver members has
been very helpful.

Thanks also to John Maclean for the faxing offer - I may take you up on it
if I can't get the standard mentioned above.

If anybody wants to know, this isn't the first dish put up here - it is
going to be one on a sort of "farm" that we have down at the
central/southern part of the island.  Some of the other dishes are even
larger, and are used by MCI among others for telecommunications.  This
particular dish will be used for satellite tracking.

In answer to Roger's questions below - I believe it is standard practice to
put these dishes in a locked "typhoon" position prior to storms.  My bet is
they cost plenty, and the poor sap who forgets to lock it down will be
paying out the you know what for a long while.  I don't believe it is
possible to (economically) construct a dish that will withstand our winds
(recorded at 155mph+ on a number of occassions in the last 30 years or so),
so locking it in position is the only way to go.

I am going to get the standard, and see if it offers any concrete data wrt
to design approaches.  If not, then I will take the manufacturer's OTM,
bring it up a bit, then take the make it stout approach.  What makes it a
bit easier is that the UBC94 calcs, crude as they are, come pretty close to
the manufacturer's OTM. In all likelihood, I think the antenna will be
ripped apart before it overturns, which from my perspective (since I didn't
design the antenna itself) is my main concern.

Thanks again all.

T. Eric Gillham PE


-----Original Message-----
From: Roger Turk [mailto:73527.1356(--nospam--at)compuserve.com]
Sent: Thursday, March 08, 2001 12:12 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Antenna Dish


Eric,

The questions that I have are:

At what conditions (wind speed, etc.) will the antenna be pointed straight
up?

Are the locking pins inserted manually or remotely?  If manually, what is
likelihood of nobody willing to mount the antenna in an approaching typhoon
to
insert the pins?

Are the people using the antenna constantly aware that the antenna should be
pointed up when a typhoon approaches?  What are the chances that they would
forget?

I think that the answers to these questions would indicate how the antenna
should be positioned for design.

I have been asked in the past to provide design calculations for small, roof
mounted parabolic (satellite) antennas.  I have requested the manufacturers
to
provide me with the projected wind area and center of pressure locations for
the antennas and never received any information.  Without this information,
I
would be hesitant to design supports for antennas subjected to wind loads.

Hope this helps.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona