[TowerTalk] Radian/Rohn availability

[Jim Lux]

----- Original Message -----
From: "Daron J. Wilson" <daron at wilson.org>
To: "'TowerTalk Post'" <towertalk at contesting.com>
Sent: Wednesday, January 26, 2005 7:55 PM
Subject: [TowerTalk] Radian/Rohn availability


> Hey folks,
>
> Anyone had any VERY recent experience with the 'new Rohn' and their
> ability to produce product?
>
> I have a customer who wanted a 100' self supporting tower for 2 - 2.4Ghz
> reflectors.  During the pricing and submittal stage, Rohn's ability to
> deliver was in question so we provided specs for a Trylon TSF which was
> available.  Now that they accepted it and are ready to pour, the
> customer heard Rohn was back in business and wants the original Rohn
> tower.
>
> Why?  They have been led to believe that there is a 'twist' factor to be
> considered, and they believe that these larger sections of Rohn Tower
> (6N,7N,8N,9NH,10NH) will provide very little twist.  Of course, it
> should be sturdy, but I have a hard time buying into the fact that these
> 2.4Ghz antennas with a 3 degree beam width are enough wind load to cause
> this thing to twist, nor do I think the path is going to care if the
> tower twists a small amount in the wind.  However, they had a better
> salesman :)

3 degree beam width is pretty narrow...
Well.. we can run some quick numbers..
For reasonably directive antennas 3dB Beamwidth = 70 * lambda/diameter

. 3 deg beam width and 12.5 cm wavelength implies

BW = 70 * lambda/diameter   (ballpark for uniformly illuminated circular
aperture)
d =  70/3 * 12.5
d = 2.9 meters... (that's about 9.5 feet...)
That's for 100% efficiency...   real antennas with 3 deg beamwidth will be
bigger.

I'd say an 10foot dish has a pretty good sail area... 80 square feet...

If the tower twists much more than 3 degrees, you'll be eating into your
link margin pretty substantially.  Do they really need a 37 dBi antenna?