The following is a summary of the replies I received following my request
for tower help along with a copy of my original posting. Many thanks to all
who replied!! By the way, you can request a copy of the Rohn engineering
catalog by sending a check for $10 US to:
Rohn
P.O. Box 2000
Peoria, ILL 61656
On Feb 8, 1996, I wrote:
>Hey Folks,
>I am in seriously contemplating putting up a tower here at my QTH in
Florida, >and was wondering were I could get information on how to make wind
survival >versus tower size tradeoffs, guy selection, etc. I am considering
a 60 to 70 >foot guyed tower with a something like a Force-12 C-3 Tribander
stacked under a >Cushcraft 402CD. Being in Hurricane country, I would like
to be able to do wind >survival comparisons between Rohn 25, 45 and 55 to
see if the heavier tower >sections are worth the added expense. I just got a
copy of Dave Leeson's book >"Physical Design of Yagi Antenna's", from what I
have seen so far, an excellent >book, but it seems focus mostly on antenna
and mast design - no too much about >towers. No sense putting up a antenna
and mast rated for 120 mph if the tower >is going to buckle at 95 - HI HI.
>Please respond direct to me at mtope@iu.net. I'll summarize and post the
>responses on the reflector.
>Many thanks!
>73 de Mike, AD4VH
Jerry, W4UKU wrote:
>MIKE, IF YOU CANNOT GET A COPY OF THE BELOW FROM ROHN, LET ME KNOW. I COULD
>POSSIBLY FIND MY OLD COPY AND XEROX JUST THE STUFF YOU NEED AND MAIL IT OUT
>(BUT SEE IF YOU CAN GET THE COMPLETE MANUAL FROM THEM FIRST). WHEN YOU CALL,
>TELL THEM YOU ARE TRYING TO DETERMINE WHICH OF *THEIR* TOWERS TO *BUY*.
>JERRY W4UKU
>A few years ago ROHN published a nice manual with engineering data on their
>tower line. Not only the ham stuff like the 25/45/55, but even the
>commercial stuff. It had their factory engineering data as well as guy
>design recommendations, concrete base specs, even dead-man design. I never
>used it for such, but I suspect copies of those pages would have overwhelmed
>the average county building permit clerk, provided you intended building to
>those specs. It also had maps showing what areas of the CONUS were rated for
>the different wind threat levels, so you could determine exactly which set
>of standards you should be constructing for. No guesswork, just good
>engineering-based design stuff.
>I don't know if it is still available, but it sure would be a worthwhile
>addition to any ham's library. It was free for the asking back then.
>Jerry W4UKU South Carolina flanders@groupz.net
Steve, K7LXC wrote:
>Hello, Michael,
> Yikes, what a challenge! According to my Atlas, you are in Brevard County
>which is a 105 MPH TIA-222-E wind zone. The first thing you have to do is
>get the Rohn catalog. The consumer products catalog has EVERYTHING up to 55G
>including drawings and specs for 110 MPH installations. If you follow their
>specifications and build it for 110 MPH, there is virtually no problem with
>the tower withstanding those winds. BTW, 100 feet of 25G will take 7.4
>sq.ft., 45G will take 7.9 sq.ft. and the 55G will take 15 sq.ft.at 110 MPH.
> That's pretty interesting in itself. The catalog can be obtained through
>most Rohn dealers or direct (309-697-4400, ask for Dana Lemmerman.)
> Antennas are another story. Physically robust antennas such as the TH7DX
>are rated from the factory at 100 MPH. The decision is "do I put up
>something strong enough (and expensive) or do I put up anything and let it
>blow apart and replace it periodically?" Either way, your homeowners
>insurance should cover it as personal property (you may need an additional
>rider.) A local ham has a "Big Bertha" that was designed to withstand 150
>MPH winds at which point the antennas would "shed" off the tower.
> Masts are pretty well documented so the crux decision would probably be
>antennas. Cushcraft's are not physically strong at all (you get what you pay
>for.) I'd probably get something suitable to begin with knowing that you may
>be making changes in the future!
> I have extensive experience in amateur and commercial tower construction
>and would be happy to provide you with my experiences. Give me a call if
>interested (206-485-7913). Good luck!
Kris, AA5UO wrote:
>Mike,
>Please seek the help of a Professional Engineer who has experience
>doing these calculations. It is the only way to be confident your
>installation is safe. Even at 10% of the tower cost it will be worth
>it. I paid $280 for a PE's expertise plus answering numerous after the
>fact questions. He prepared a plan that I submitted to the city that
>was accepted with no questions asked.
>73
>Kris AA5UO
>mraz@aud.alcatel.com
Gary K7FR wrote:
>Mike,
>Don't even consider for a nano-second putting up 25G. It's a good utility
>grade tower but for any serious antennas and wind it's a big loser. Use 45G
>or if you feel real generous 55G. You'll get a better/safer/more
>comfortable installation. I have 110' of 45G with a KT34XA and 40-2CD and
>find it to be the most comfortable to climb and work on. It doesn't wiggle.
>We get 80-100mph winds every spring and I've not noticed ANY movement in the
>tower. I've even worked on it in 40+ winds. It's more expensive and
>heavier per section and also requires a little more skill to erect but it's
>worth it.
>73 Gary K7FR
>Antenna Farms
Ray, ND8L wrote:
>Hi Mike...
>I'm probably the 50th guy to suggest this...but I would look at the
>C4XL...which gives you a little more oomph than the C3 and two elements on 40
>on a 32' boom.
>I've got a C4 that started out as a C3 and it works real well on
>20/15/10...so so on
>17/12 and domestically pretty well on 40.
>If money is no object :-) I'd take a look at the 5BA and one of Force 12s 40
>meter beams. But hey...it's real easy to spend YOUR cash.
>73, Ray
Stan, W7NI wrote:
>Hi Mike,
>I can certainly sympathize with your desire to know how to correctly design
>your tower installation so it won't fail. We had quite a thorough
>discussion here a couple of months ago where it was pretty much concluded
>that all of the engineering design expertise needed to do this job right
>could be put into a software program that could be used by the average ham
>much the same way as antenna design software is used today. The problem is
>that anyone who writes such a program is assuming a massive amount of
>liability in the event that one of the tower systems designed using the
>program fails. When a tower comes down, real damage can occur to people and
>property. If an antenna blows apart, the pieces are generally light enough
>that nothing gets hurt (except the antenna!)
>It turns out that there actually IS a place where you can get the
>information you seek. The Rohn tower company offers various services to
>their customers regarding evaluating designs using their towers. Here are a
>couple of examples of the services they provide and what they typically
>charge for them:
>Product review of Standard Catalog Towers (for other than catalog antenna
>loads): $1000 per tower.
>I believe this is the service you are asking for. What you need to do is
>get ahold of a copy of the "Rohn Ham Tower Catalog", determine the square
>footage of the antennas you plan to use, and see how your installation
>compares to those published in the Rohn catalog. Once difference I noticed
>is that Rohn never talks about stacking any antennas on a mast above the
>tower. Their loads are always shown to be at one place -- right at the top
>of the tower. $1000 may seem like a lot to pay for this information, but it
>just reflects the cost of Rohn's liability insurance which they MUST have if
>they are going to pass out this kind of information.
>Here is another service you might need if your city requires it before
>issuing a building permit:
>Foundation Drawings and Calculations (Soil analysis by others) (Anchor
>Blocks, Base Piers, Pier & Pad, Caisson, Mat): $1,500 per type.
>I am not aware of any ham who has ever taken advantage of this service from
>Rohn. It just costs too much. Besides, I suspect you won't really be able
>to get a good picture of the "tradeoffs" without having Rohn submit a bunch
>of different designs for $1000 EACH . . . Oh yes, the above prices are
>DEALER PRICES and you will have to pay considerably more unless you are a
>Rohn dealer . . .
>Probably the real way to get this done is to cultivate a personal friendship
>with a qualified structural engineer and offer to swap him an equally
>valuable service if he will design your tower. You could give him a free
>heart transplant, for example, if you were a cardiovascular surgeon . . . or
>perhaps a new Ferrari if you are a car dealer . . .
>Stan W7NI@teleport.com
Bill AB5YG wrote:
>I have 70ft of Rohn #25 with a cushcraft 4elm 10M beam (16ft boom) at 83ft
>(on 20ft mast), 10ft below that is a Force 12 4elm 15M Beam (24ft boom) and
>10ft below that mounted on a Tic-Ring a Force 12 4elm 20M beam (30ft boom).
>I have three sets of guys on the tower With the Rohn Torque Bars and guy
>equalization plates. Rohn 25 is know to twist down! Even with all the guys
>I have the torque of all the beams twist the tower. I thought I was going to
>loose the tower & beams this fall during the "close call" hurricanes. It
>stood up well to close to 70MPH winds - I'm pretty sure it would have been
>blown away (twisted down) if the winds reached 100MPH.
>I feel that I should have spent the extra money and gone with Rohn 45 - This
>is what all my "tower" friends recommended - I was looking at saving bucks
>--- There is also a big difference in the "feel" of climbing the 45 --- Feels
>solid!!!
>Got to run ------ 73's Bill AB5YG
Pete Smith <n4zr@ix.netcom.com> wrote:
>Mike, if you don't already have it, you should get the Rohn catalogue. For
>$10 they give you a lot of information that bears on your problem. I am
>told (by a ham who is also a commercial Rohn tower installer) that the wind
>load numbers they give (70 and 90 MPH) are quite conservative. I don't know
>what your EIA zone number is, but somebody will doubtless tell you. There
>is an awful lot of good conservative engineering practice in the catalogue,
>in any case.
**************************************************
** Michael Tope, AD4VH (ex KD8NS, KA8ESD) **
** 200 Easy Street **
** Melbourne, FL 32934 **
** Tel: (407) 259-7494 **
** Email: mtope@iu.net **
**************************************************
"It is the empty space inside the vessel that makes it useful" - Lao Tzu
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