Rohn's data regarding the self-supporting capabilities of 25G (RH-25) is
based on well-established structural engineering calculations with a
significant safety factor thrown in. I wouldn't be surprised if they've
also performed some finite element analysis computer modeling in recent
years to back up their calculations.
With all due respect to Steve, his statements are not based on engineering
calculations or FEA modeling - nor is he a licensed structural P.E. He has
also stated often to do what the manufacturer says.
I'd say Radian/Rohn would have my vote for starters. You may also need to
have a structural P.E. licensed in your state do another set of calcs based
on your specific soil type and local windspeed zone classification, because
Rohn's calcs don't take every soil type into account.
[mailto:email@example.com] On Behalf Of Robin Midgett
Sent: Friday, May 12, 2006 11:02 AM
To: Dave Fuller; firstname.lastname@example.org
Subject: Re: [TowerTalk] Rohn Self Support Chart Says.......
Hmm...that's interesting, thanks for the file.
Given that Steve has maintained that 25G isn't self-supporting at any height
literally dozens of times on this reflector, I wonder if that document from
1987 has been superceded.
I know that the tower is now manufactured by others (not Rohn); is that the
reason you refer to it as RH-25, as opposed to the long tradition of 25G?
I agree..temporary guys are necessary at least for antenna & feed line &
tower installation purposes. The risk beyond that lies entirely with the
owner. Additionally, if this tower were erected and not guyed, anti-climb
panels should be installed without question.
Without the panels & guys, if some unwary person were to climb this tower,
he/she & the owner would be at terrific risk.
At 09:17 AM 5/12/2006, you wrote:
>I have the Rohn Chart that shows RH-25 can self support 1.5 sq.ft of
>windload at 70 MPH with no ice.
>For 90 MPH is self supports 1.7 sq. ft 30 feet of height (no ICE). The
>specs are for 3 - 5/8 feedlines and round antenna members.
>If I were doing this and had to climb it, I would install temporary
>rope guys and climb in no wind conditions.
>20 ft of RH-25 will self support 6.9 sq feet of antenna at 90
>mph. I am really comfortable putting up RH-25 sections with a Gin
>pole 2 or 3 sections above the temporary guys but not more... so this
>fits what I feel is safe when I am on the tower.
>Robin Midgett wrote:
>>Yes, I can tell you...No, absolutely not! 25G isn't self-supporting at
>>any height. Additionally, if you were to erect this 40' tower without
>>guying it, someone would have to climb it and install the
>>antenna...making for a very dangerous situation. The ice loading
>>situation that someone else mentioned is another reason not to do this.
>>Granted, hams have used this technique and gotten away with it for
>>years...but that doesn't justify doing it. You should either guy the
>>25G installation or use self-supporting tower.
>>At 05:32 AM 5/10/2006, you wrote:
>>>>[mailto:email@example.com] On Behalf Of Martin & Ann
>>>>Sent: Monday, May 08, 2006 8:37 PM
>>>>Subject: [TowerTalk] self-supporting rohn 25g??
>>>>Can anyone tell me if it's OK to install a 40' tower, made from four
>>>>10-foot sections of Rohn 25G, as a self-suppoting
>>> tower? The antenna that wpould be on the tower is a small
>>> omni-directional circularly-polarized FM antenna for 95.9 MHZ, so it
>>> is small with not much windload. How big does the cement base have
>>> to be? Locally, the minimum concrete order is 4 yards. We are
>>> located in upstate NY. 4 yards would be somewhere around a 4.5' X
>>> 4.5' X 5.5' foot base.
>>>>Thanks and 73...
>>>>Spirit And Truth Christian Radio WJIH-LP 95.9
>>Robin Midgett K4IDC
>>615-322-5836 office - rolls to pager
>>TowerTalk mailing list
>Robin Midgett K4IDC
>615-322-5836 office - rolls to pager
TowerTalk mailing list
TowerTalk mailing list