[TowerTalk] Drive on Mast support base - All ready homebrewed...

[Jim Lux]

At 10:11 AM 7/28/2005, ersmar at comcast.net wrote:
>TT:
>
>      Good solution, but guying may be needed depending on antenna load 
> (2M Yagi vs HF dipole wires vs UHF vertical.)  Concrete blocks could be 
> used as anchors at guy points in parking lots.  Be sure you clearly mark 
> the blocks, if used, as pedestrian hazards.
>
>73 de
>Gene Smar  AD3F
>
> > ----- Original Message -----
> > From: "Matt Patterson"
> >
> > > This thing would be super easy to homebrew...
> > >
> > > Then purchase one of those fiberglass masts you see on ebay all the time.
> > >
> > http://www.qsl.net/wb3gck/mast_support.htm
> >
> > Not as fancy, but still workable...
> > And AOL Ham keyword: CHEAP/EASY  to do....
> >

In all but the lightest of winds, guying is almost certainly needed, unless 
you're willing to tolerate a mast failure.  In lots of portable type ops, 
though, having the mast come down (or bend) if a big gust comes up is a 
perfectly acceptable way to operate.

I did some analysis on using a car to stabilize a vertical mast with 
windloading. I wanted to see if it would rip the rack off the car, for 
instance.

http://home.earthlink.net/~w6rmk/antenna/mastcar.htm

The calculations were fairly conservative (large mast diameter, 50ft high, 
80 mi/hr wind) but the forces get pretty big, pretty fast.  A concrete 
block isn't going to hold a 20 pound load without dragging, and even in a 
40 mi/hr wind, you only need about 5 sq ft of total area to drag the block