At 02:23 PM 9/12/96 -0400, you wrote:
>Hi,
>
> I have a friend who has a very small lot, and would like to put
>up a tribander on his roof. Instead of a roof mounted tower, he would
>like to have a carpenter put the mast through the top of his roof
>(somewhere in the peak), and secure the bottom of the mast to hist attic
>floor, which will undoubtedly involve some special bracing.
Dave, I don't recall the article but I have three personal experiences with
roof mounted beams.
When I was a student at the University of Missouri I mounted a 2L quad
on a mast that project through the peak of the roof (well, it was offset a
couple of inches to miss the main board that ran along the peak). The
mast was about 20 ft long and the old house had a pretty high ceiling
in the attic, above the second floor. I bolted the HAM-M to the floor
(which was the ceiling of some of my house mates' rooms) and used a pretty
simple wooden bearing in the roof. The mast went about 12 ft above the
roof to the center of the quad. I just recall working EP on 20M long path
every morning--breaking big pileups with the thing. (circa 1964) I put some
grease around the mast and then built up some roofing tar to make a little
mound around the mast (the tar did not stick to the mast due to the
grease). I then made a funnel/umbrella around the mast to protect the
tar and shield the gap from the rain.
The only drawback was the noise from the rotator annoyed my roommates
a bit. I would do it again, but with the rotator mounted on something that
acoustically insulated it from the floor of the attic. Such as bolting it
in the
center of a long 2x12 and securing the ends of the 2x12 to the attic
structure with some sort of acoustic dampening material. The attic was
accessible with a stairway making rotator work an easy, indoor job.
One further note--the house was condemned after we moved out! (Well it
was 85 years old and the University wanted it for a parking lot.)
My second experience with a roof mounted antenna was when I was at
the University of Colorado in Boulder in the late 60s. I was the manager
of a girls rooming house (!) and the owners in Nebraska said I could
put up an antenna if I made no holes in the house. I took the challenge
seriously and built a Vee shaped base of 2x12s and angle iron for the
mast that would sit on top of the peak of the roof to provide the torque
resistance for the mast and padded the underside of the thing with carpeting to
eliminate any chance of roof damage. The house roof came to a peak that
was only about three feet long (almost a point) and had dormers on all
four sides. I placed a pipe underneath the overhang of the roof on each of the
four dormers that was held up into place by the tension from the mast guy
wires that were installed on each end of each pipe. This resulted in 8 guy
wires for the
12 ft mast but no attachment to the roof or house at all.
Boulder is famous for their 140 mph winds and this system came through
a lot of wind in fine shape. The antenna was a Mosley Classic 33 and the
rotator was a HAM-M mounted just under the antenna. When I left it was
easy to remove the system and not a single hole was made in the roof or
house. Of course it did require a unique house with four dormers at 90 degree
spacing.
Guying to the roof requires significant understanding of the forces involved
but can be done with the right reinforcement techniques to spread the
load over a wider area than what a single guy point might do. My two
installations
were each only up for a year or so, but it does point out that with a little
ingenuity what can be done with roof mounted antennas.
My third installation was done for a ham who had received permission to install
an antenna when he built his house if there were no ground mounted towers.
He (AD0I) designed his multi-story house with a very large wooden chimney
structure that housed the insulated chimney pipes in one part and the
Rohn 45 tower in the other part. The tower was installed with a concrete
base on the floor of the basement so that climbing the tower involved
going down to the basement, opening a closet door and climbing about
35 ft, while still inside the house! At the top of the chimney structure
was a trap door installed on the roof. You just had to pop open the
trap door to continue the climb on up the tower to about 10-15 ft above the
top of the chimney. I don't recall what make of tribander was installed but
this installation has been up for a couple of decades in Boulder's famous
winds.
Hope this helps trigger the imagination.
73 John
John Brosnahan W0UN
24115 WCR 40
La Salle, CO 80645
"Radio Contesting IS a Contact Sport"
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