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Antenna Support

Jul 7th 2012, 21:33

KD6MZC

Joined: Apr 4th 1998, 00:00
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I am interested in information on the mechanical design of antennas and their support. Of specific interest is the basis for calculating wind loads and deflection criteria.

In my professional life I am a Structural Engineer so I would appreciate all information from the basic to detailed technical.

Given that aluminum is used a lot I would also be interested in what grades of aluminum are typically used in antenna structures.


Mark
KD6MZC
Jul 8th 2012, 01:00

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Hi Mark,

The Electronic Industries Association publishes EIA-222F
Structural Standards for Steel Antenna Towers and Antenna Supporting Structure

David Leeson W6QHS published an excellent book, Physical Design of Yagi Antennas, but it is now out of print and relatively expensive on the used market.

Array Solutions has a useful page on wind load
http://www.arraysolutions.com/Products/windloads.htm

Yagi Antennas are typically built using 6061-T6 or 6063-T832 aluminum tubing.

Zack Lau W1GT
ARRL Senior Lab Engineer
Jul 8th 2012, 05:13

KD6MZC

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Zack

Useful references. There is much to learn.

Some of the references are dated in that the building code provisions have recently changed and the way wind loads are calculated are different. The final result may not be much different in most cases still one wants to comply with the current provisions.

The EIA/TIA 222-G standard is expensive.

Lack of discussion regarding need to get building department approvals, where they enforce the building code.

Some of the information I found reflects engineering knowledge while other information suggest that the author is passing along "conventional wisdom" some of which is wrong or simplistic.

Mark
KD6MZC
Jul 8th 2012, 20:15

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

http://www.antennazoning.com/
Here is an excellent site by Fred K1VR, on the topic of Antenna Zoning

http://www.arrl.org/shop/Antenna-Towers-for-Radio-Amateurs/
An excellent book on the practical aspects of putting up a tower by someone who does it professionally.

As I understand it, the current legal climate makes it very hard to get someone with the appropriate credentials to write a book on tower engineering for hams.

Zack Lau W1VT
ARRL Senior Lab Engineer
Jul 9th 2012, 01:24

KD6MZC

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
I will look further at the court rulings posted but it is my impression that the focus is on zoning issues. My focus is on the structural engineering of the antenna and any supporting structure.

Where there are building codes it is necessary to comply with the technical requirements in the building code. These requirements go beyond TIA/EIA 222G.

In many states for anything beyond a small to moderate size antenna a professional engineer registered in that state is supposed to prepare the drawings and any calculations for submission to the building department. My impression is that very few professional engineers have the necessary expertise. This is a niche specialty.

What probably happens is a local engineer who is not very familiar with towers prepares the calculations. This is probably not a problem in most cases unless the tower is very tall, wind loads are very high, or icing is an issue.

In many parts of the country the building codes are loosely enforced and this is especially true for antennas which many building officials are not familiar with. This goes a long ways towards explaining why this isn’t an issue in most cases.

It will be interesting to understand the ability/willingness of tower manufacturers to satisfy the requirement that the tower was designed by a professional engineer in the state it is sold. Are their engineers licensed in all states they sell towers and if they are do they take responsibility for the design of the bracing wires and the foundation structures. This gets messier when you move an antenna to a new site and the original professional engineer is not available.

I believe the liability issues of a book are manageable. Because the situations where there is a real need for the book have to do with situations where a professional engineer is involved the secret is to aim the technical portion of the book at professional engineers with a portion advising the purchaser of the tower. The book could be used by both the local engineer and the purchaser of the tower. Maybe what is needed are two booklets.

At the root of this discussion is the question of what your average ham can reasonably do and when he/she needs other expertise. There are no simple answers.

While there are a lot of nuggets of useful information in the posted information some of the “conventional wisdom” by those who have erected towers is questionable.

Mark
KD6MZC
Jul 9th 2012, 02:01

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
http://www.arrl.org/locate-a-vce

Here is a database of engineers with expertise in tower design.
Jul 17th 2012, 13:17

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0

What hams really need help with is the mixing of trees and towers--in many communities it is politically wise to keep as many trees on the property as possible. Yet you also need to remove trees, as a common failure mode of towers is to have a tree fall on a guy wire, pulling the tower down. An analysis of how optimally mix the two would make a great article.

Last year was a bad year for trees in New England--we had a tropical storm that dumped enough rain for pine trees to topple over. Then we had an heavy wet snow that covered fully leafed out deciduous trees--they weren't designed for such heavy loads--which ultimately resulted in numerous power failures--took ten days to restore power in some neighborhoods.

Zack Lau W1VT
ARRL Senior Lab Engineer

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