[TowerTalk] TowerTalk Digest, Vol 72, Issue 43

[John Lyles]

Donald 
Thats a lot of questions. I will attempt to reply to the ones I know the answers too. More experts on this list may have more opinions. I am installing a similar tower right now, so this is my experience being shared. 

1) not sure if you CAN straighten it if the foundation has tilted. If you try to force it with guy wires, you will destroy that 25G tower, put undue stresses in the lower sections below your guys, esp above the concrete. That cubic yard of concrete, if it has shifted, is not going to respond to the guys tension before the tower deforms. It might be worthwhile to just cut it off the base, and either make a new concrete foundation adjacent to it, or try place a pier pin anchor on yours, by drilling to place studs. 

2) Yes, if you can replace it with the thrust bearing flat section, better. You can stand on the 25AG rungs just as well, when working up at the antenna. 

3) 30' guy horizontal spacing is about the minimum you'd want for that tall a tower. It loads the tower with a lot of down thrust. Normally try to get the guy anchors out at 70-75% of the height at minimum. Your upper guy will be somewhere below the top probably, like 42 feet. The lower guy will be down in the 20-25' range I suppose. That heavy pipe, will it withstand the constant 800 lbs of tension that you need for each pair of guys on it, as well as the additional wind-driven tension? You need structural analysis before you can decide this. You need to know what the wind load of your planned antennas will be, as well as the max wind and ice loading that your county experiences. You get this on the web. Mine is 75 MPH and 10 sq ft of aluminum up top, with little icing. 

I am finishing up a 25G install at QTH this weekend, and it is 46 feet tall. It has 2 sets of guys, out at 32-33 feet from the base. I used Hubble Bust-type anchor rods and plates, which are sunk 6 feet into a diagonal hole 45 deg. With good soil, they are rated for up to 10,000 lbs, and are only $25 an anchor. Power company uses them for guying poles. I trusted these, but using pipe and concrete like you are suggesting, hmmm, you better have an expert comment on this. I would be afraid of having the concrete shift for those too, in the wind, esp if your ground is that soft. Best to do a real concrete dead load deep in the ground with the force pulling directly in line with the anchor rod (not pipe). 

4) sorry no comment on the coax. 


> From: Donald Hofmann <electroubleshooter at hotmail.com>
> Subject: [TowerTalk] rohn 25g questions
> 
> I installed 30' of Rohn 25G in the early 90's. It is self supporting with 3' of the base in concrete (3x3x3'). I had two Channel Master antennas on it.
>  
> Now that I am into ham radio, I want to heighten the tower to 50' (actually 47') guy it and put a beam or two on it.
>  
> Here are my questions:
>  
> 1. Over the years, the tower has started leaning- probably from the shifting of our soil. When I guy it, how much should I try to straighten it? I would guess that it is leaning about 5 degrees, as it is visible with the naked eye.
>  
> 2. I will have to replace the current 25ag top section so as to use a 2" mast. I am looking at the 25ag4 flat top and tb-3 thrust bearing instead of the 25ag2. My reasons being- the flat top has tabs for guys avoiding the need for me to buy a star bracket or other assembly and two, the flat top will be a good place to stand while attaching antennas. Also the bearing makes less work and strain for the rotor. Comments?
>  
> 3. Due to space restrictions I can set the guys 30' from the tower base. They will be attached to 7' of heavy pipe with 3' in the ground in concrete. Is this adequate? I will use two guys per side. 4' high for the guys should help increase the guy angle as well as increase their height to keep things from hitting them.
>  
> 4. I plan on running the coax down the tower to about the 15' level then across the air into the gable end of my shack. I will run a piece of guy wire to support it and then loosely tie the coax and rotor cable to it with cable ties (like a clothes line). It is about a 40' run so I am sure that it will sway some in the wind. Should I use LMR400 or LMR400 flex so that it will not break in the wind? The total run will be about 125', is LMR400 adequate or should I run something better?
>  
>  
> Thanks
>  
> W5DWH
> _________________________________________________________________