I guess since the thread is still alive, and because I use my Elecraft rigs with said tower :) I'll wade in here, because I spent a fair amount of time researching this two years ago before reinstalling my Wilson TT-45, which is very similar. Everyone is right, one way or the other. The tower wind curve I have shows 3 square feet of wind load for a total tower height of 43 feet in a 78 mph wind. Another 50 mph curve supplied with the rotating base is done at 50 mph, and says 12 square feet at a total height of 45 feet. But both curves, as well as the more recent US Tower data, rely on the use of a house bracket in the analysis. A much more recent US Tower doc shows 4.8 square feet of wind load, for 85 MPH 3 second gusts, but with the tower at a height of 21 feet. This was from a California PE analysis, and it also referenced the house bracket. So the answer, "it depends" depends on at least wind speed (or gust) used, what base, the use of a house bracket, height of the mast in the top section, and what the current sq ft numbers for your antenna happen to be, which seem to be changing in some cases :). After crunching some numbers, I decided to limit my use to 34 feet self-supporting with a hex and a rotating base . It's definitely worth doing the math. I'm happy to share PDF's of the reference stuff with anyone that needs it. Scott ka9p (sorry Eric) In a message dated 7/13/2016 5:08:53 P.M. Central Daylight Time, [email protected] writes:
Hi Mike, I don't know where the 3 SQ-FT comes from. US Tower does not publish ratings for the MA series any longer. I have had an MA-40 since 1982 and at that time the rating was 10 SQ-FT @ 50 MPH winds fully extended. I have confirmed this with US Tower in the past. I was also told at that time that they do not rate the tower retracted. There have been some new regulations concerning tower ratings in the past couple which is probably why they do not list it now. I have had a 3 Element SteppIR on this tower since 2006. The HRO website still lists the rating at 10 SQ-FT. That being said, I do retract the tower if winds of 50 MPH are predicted or if I am leaving for any length of time. My base is 3 X 3 X 5 which was recommended at that time and I have the drawings for that. I think the 3 SQ is indicating the size of the extended portion which is 3 inches square. Date: Wed, 13 Jul 2016 04:01:47 -0700 (MST) From: Mike K2MK<[email protected]> To:[email protected] Subject: Re: [Elecraft] Need advice on Small Tower Message-ID:<[email protected]> Content-Type: text/plain; charset=us-ascii Hi Terry, I'm moving and I've just sold my MA40 with the MARB40 tilt over/rotator base. It's a fine tower for small loads. Be careful, it's only rated at 3sqft load when the tower is cranked down to the 21 foot level. I had a 2 element SteppIR yagi on it and I would crank it down if winds over 20 or 30 mph were forecasted. Cranking it up and down is very easy on the arm. It cranks easily but requires 100 cranks. Tilting it over and cranking it down and back up requires much greater effort until the mast is at the 45 degree angle. I would have liked to have a power driven winch for that operation. The foundation for this mast is substantial with lots of rebar. I'm selling my house and just had the top 12" of concrete removed so that I could replace it with grass. It took a crew longer to remove the 12" then it did for the crew to dig and pour the foundation in the first place. I'm thankful I didn't have to any of the work. This mast can actually be handled by one person if you have moderate equipment to help. I had a wheeled lawn cart for rolling it around and a Harbor Freight 1 ton shop crane for taking it off of the flat bed delivery truck and helping to engage and dis-engage the mast into the MRB40 unit. With two people it's a very simple job. All of my experiences were good and given the opportunity I would not hesitate to purchase another one. I have a personal website with lots of photos. Contact me directly if you want the link. k2mk at comcast dot net 73, Mike K2MK ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
