[TowerTalk] Rohn Spec's - 45G Side Arm Mounting Hardware

[Kurt Andress]

Greetings to all,

Remnants of a recent thread....

Due to a question posed to me last week, I spent some more time looking
at the Rohn 45G tower configuration drawings and found something that
may be of interest to some of the folks on this reflector.

The relevant drawings are the 45G configurations:
C870401 R2
C870417 R1
C870478 R1
C870479 R1
C902042 R1

They appear in the latest Ham & Commercial catalogues.

The specific point of interest is Note 4, concerning the possible
allowance we can use, to our benefit, when we consider a tower that does
not use the P/N SA253UA (DWG C821662) side arm mounting assemblies.

At first blush, and as discussed on the TT reflector in the past, it
appears that Note 4 says we can add 8.0 SqFt to the allowable antenna
load when we don't use these side mount assemblies.

Well, it turns out that this is not correct.

After chasing the issue for a while, I figured out how these devices
were treated to arrive at the 8.0 SqFt of "Effective Projected" area
stated in Note 4.
The nomenclature used may have posed part of the problem.

Note 4 is talking about the "effective area" of the assemblies,
including drag coefficients, when looking at their projected areas, when
symmetrically placed about the tower.

To convert this to the simple projected antenna area figures used in
Note 2 (that have not yet applied the drag coefficients), we have to
look at the details of the assemblies, what is comprised of angle stock
and what is comprised of tubing (the EIA spec uses different drag
coefficients for each), the exposure of each component of each assembly,
placed as described.....etc. 

The result is:
Taking the three side arm mounts off our amateur tower allows us to add
6.7 SqFt of round membered yagi to the value that appears in the oval
outline in Note 2.

Not a big deal, but offered for the sake of accuracy. 

Since, I used the 8.0 SqFt adjustment in the guyed tower study
presented on my website, I have corrected all of the information therein
to reflect this change, and revisited the entire presentation.

No late breaking news there, still tells the same story with different
numbers and coments. 

Thanks to N4KG for posing the original question!


-- 
73, Kurt, K7NV 

YagiStress - Software for Yagi Mechanical Design
Visit http://www.freeyellow.com/members3/yagistress/

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