[VHFcontesting] Masting . . .

[Fred Lass]

Note that water pipe has a rated yeild strength of 30,000 PSI.  Most mast materials are rated at 80,000 PSI.
 
When you buy pipe, 2 inch pipe is 2 3/8" OD; 1.5" pipe is 1.9" OD wall thickness of .145, but 2" tubing is really 2" OD.
So, in round numbers, a real 2" mast with .25" wall is ten times as strong as a 1.5" schedule 40 pipe. 
Normal wall thickness of pipe is schedule 40, thicker wall is schedule 80.
 
So, pipe is fine for small antennas that are not too far above the top of the tower.  That's why you often see 6 meter antennas lowest on the mast.  For stacking 6 meter beams, a real mast is necessary.
 
My friend Saul, K2XA, didn't believe me and bought a 1.5" schedule 80 pipe and mounted a 6 element 10 meter beam 20' above the top of the tower.  I refused to install it for him, so he did it himself.  It bent in a 50 MPH wind.  Removing the bent mast was the hardest tower job that I ever did.
 
73,  Fred K2TR  


"S.J.Swanson" <swanson at ticon.net> wrote:KC8QVO, Steve said:

" . . . Also, what does everyone recommend as a mast? Array Solutions sells some REALLY NICE PE certified masts, but they are VERY expensive. I was thinking about going to the plumbing supply store and getting a 2" galvanized steel pipe. . . . " 

In a direct communication to Steve I had suggested 2 inch o.d. galvanized pipe which is 1.5 i.d. inch water pipe. The 2 inch nominal is actually 1 and 7/16 inches which means that the walls are 1/4 inch or 7/32 inches. The stuff is bullet proof and a 15 foot spliced piece with two VHF and two HF beams survived a wind event that pulled my tower away from the house and twisted the two lower sections of tower. The antennas, top two sections of tower and the mast are still pristine and in use. 

I use this pipe because 26 years ago, HyGain used it as their "gold standard" when describing the process for shimming a mast in the Ham IV rotator. I do not use the new stuff --I priced it today, it is $33.00 per 10 foot section. I go to a salvage yard and get used 1.5 inch pipe. It may have rust on the inside but I have found that pipe with no external pitting or rust is as strong as new and only runs 40 cents per foot. It is sold by the pound at the junk dealer. 

When it is necessary to splice in order to get a desired length, I take the pipe to a hardware store and have them extend the threads beyond the standard for a water seal. This in conjunction with a standard coupling gives plenty of purchase to give a strong joint. Once assembled I drill through the coupling and pipe and install tension pins (roll pins) to prevent the joint from unscrewing. (It did happen once!) 

The down side is that the stuff is heavy. However, I have a Glen Martin Hazer on each of my towers and I am working from a roof top or from the ground. Easy enough to use a block and tackle on the tower to lift the mast above the Hazer and lower it into the bearing. Of course once it is in place, weight is a non issue. 

73, Sherm KB9Q, (EN52vv)

swanson-KB9Q at ticon.net
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