roof mounting help

[K7LXC@aol.com]

In a message dated 96-09-21 15:12:01 EDT, you write:
>	1. Has anyone had any experience with this particular brand of 
>	   tripods?  I believe I've heard good things about some of the 
>	   products made by Glen Martin, but I have no experience with
>	   roof tripods.  (The wind ratings he read to me will be more 
>	   than adequate for this antenna.)

Hi, Charlie --

    I just put one of the 8 footers up yesterday (my second roof tower
installation) with a C-3 on it and they seem to be adequately strong.  They
are actually a pretty good option for antenna mounting.  Hy-Gain offers a
whole package of roof-mounted tower, antenna and rotator for about $800.00. 
      The only thing I don't care for is that the instructions for the Glen
Martin towers want you to anchor them with lag screw into the roof joists.
 That means that you have to mount them EXACTLY in the right place and assume
that your roof has exactly 24 inch centers.  I prefer to re-drill the
mounting foot with one hole big enough to take 3/8 inch allthread and then
run it through 2X4 stringers, or backing boards, that go across 2 or more
trusses.That spreads the forces out over a bigger area.  The result is a nice
sturdy reliable little tower.
>
>	2. Is it possible for him to safely mount the antenna on such a 
>	   long mast above the top of the tripod?  Intuitively this seems 
>	   like it will put too much of a strain on the tripod.  (I also
>	   don't have any idea how the antenna can be safely installed
>	   by the worker.)  It would seem to me that the tripod will need
>	   some sort of guying if the antenna sits very high above it.
>
      The LXC Prime Directive is "DO what the manufacturer says"; they
probably don't recommend it.  Installing any antenna up a mast is a simple
matter of installing temporary steps on the mast.  Guying the tower will
certainly add some strength to the installation but these need to be strong
and well-engineered, not just an eyescrew screwed into a joist.  I'm sure our
more engineering-oriented members will have more to say on that.  Take a look
at Tony's, K1KP, recent article in QST on a house-bracket installation to see
what real live engineering involves.

73,  Steve  K7LXC

    TOWER TECH -- professional tower supplies and services for amateurs

--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 K7LXC@contesting.com
Sponsored by Akorn Access, Inc & KM9P