Antennas on tripods - how tall?

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obsolete changed to k0fe:
We are preparing to put a vhf/uhf omni (vertical) antenna on our roof using a tripod. I'm wondering how high up it is safe to go with either a 3ft or 5ft tripod. We will probably use a 5ft or 10ft mast. The antennas we are looking at range from 6'(3lbs) to 17ft(6lbs).

We've even considered using a 30ft telescopic mast instead of the 5ft mast/pole with the tripod, but have no idea as to what would be safe/practical.

Recommendations or pointers to guidelines for this type of mount?


Chris J. Smith:
If you use a tripod to put an antenna on a roof you have to realize that the the wind loading factors multiply the higher you go.  Even if the mast height is short, a tall antenna puts excess strain on the attachment point of the tripod to the roof.  The only combination that may not require guy wires is the short antenna on a five foot mast.  

The danger of having the tripod torn out of the roof if heavy winds come along almost make it imperative that you use guy wires, even on installations that aren't too tall.  Guy wires are cheap insurance if you look at the cost of roof repairs and a replacement antenna/tripod assembly--and you may have a hard time with an insurance claim (improper installation) if you don't use them.  There are guy lines available made out of both aluminum wire and kevlar rope.  Three way guying is the minimum, four way provides extra support and safety in an area where winds could be a problem.

Guying is strongly recommended at a height of ten feet even with tripod mounting.  If you use an extendable mast to go higher, guying is necessary.  On a thirty foot mast, two sets of guy lines are needed.

You state the installation is to be on a roof, so I gather it is to be semi-permanent.  The only time guying isn't really needed (but still recommended) is on a temporary, low installation.  

Chris J. Smith:
Oops, I forgot to say where to attach the guy wires--just below where the antenna is attached to the mast, and on a thirty foot mast, approximately ten feet below the first attachment point.  Also, the further out you can go with the guy wires, the better off you will be, but it should not be necessary to go out more than twenty or twenty five feet (horizontally) from the bottom of a thirty foot mast.

Guy wires do not have to be very tight--that puts excess downward pressure on the mast assembly, they just have to be snug.  If the mast does sway a little in heavy winds, it isn't a problem.

obsolete changed to k0fe:
Thanks for the reply. I found several other posts recommending the GME 4 leg roof tower. I think I'm going to go that route just to be on the safe side.

Bob Lewis:
For years I've put yagi type TV antennas on the roof using inexpensive 3-foot tripods and 5-foot masts and never had a problem. I had one on my own roof for 20 years without an issue. It even went thru a hurricane.

I've seen people put 10/15/20M yagis and a rotor on a heavy duty tripod (unguyed) with no issues. Such a large installation needs some reinforcement under the roof at the attachment points - not just screws into the plywood.

Unless your antenna is very long you shouldn't need any guying as long as the tripod is properly attached to the roof. It's not a bad idea to put some pieces of 2x6 under the roof at the tripod leg points and attach them to the rafters to provide a solid mounting point for the tripod.

To prevent leaks, put roofing tar on the bottom of the leg mounts before setting the tripod in place. Then run galvanized lag bolts thru the holes in the leg mounts, thru the roof, and into the 2x6 supports under the roof. Then put a good coat of roofing tar over the entire foot of the leg mount.


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