On Sun, 17 Oct 2004 16:41:41 -0500, "JerryMouse" wrote:
Edwin Pawlowski wrote:
"John Sullivan" wrote in message
...
Are you sure it is 3.5", my dish is mounted on 1.5" galvanized iron
pipe (available at most good sized hardware stores). If that is what
you're looking for, then yes Home Depot should have it (check in the
fence section,
chain link pole)

Did you see the type of dish he has? Yes, he need a large strong
pole.

No he doesn't. He should put the dish on the ground. Do you think 12 feet
out of 24,000 miles is going to make any difference?

How's he going to point it at the satellite when it is laying on the ground?
The flattest elevation angle in the mid-latitudes is 49 degrees for a bird
that's at the same longitude in the Clarke belt as the ground location,
and gets steeper toward either end of the arc. The lower lip of the dish
must clear the ground at minimum beam elevation (dish 90 degrees to
the Earth's surface) in order to cover the entire arc.

That means the mount point must be more than 5 feet above ground level
for a 10 foot dish. But that's not enough if he wants to maintain a reasonable
antenna noise temperature. To do that, the major dish sidelobes must
clear all terrestrial obstructions.

In flat terrain without a raised horizon, and assuming a typical 2 degree
half angle for the first major dish sidelobe, that means the bottom edge
of the dish needs to be at least 3 feet above ground level. For rougher
terrain, or locations where there are far field obstructions (buildings,
trees, etc) out toward the horizon, the dish will need to be higher.

So *at minimum* he needs a mount pole that sticks 8 feet out of the
ground. A 12 foot pole lets him do that, with 4 feet set in concrete in
the ground to resist the overturning moment.

Besides, putting a ten-foot circle of metal twelve feet in the air is a
disaster waiting for a victim.

That's why he needs a heavy pole. 3.5 inch diameter pipe is actually
a bit on the light side for this size dish. I have my "small" 12 foot dish
mounted on 6 inch pipe. The larger one (a 10m Scientific Atlanta dish)
is mounted on a 24 inch diameter heavy wall steel pedestal designed
for the dish.

The overturning moment on medium to large size dishes is very
high in even moderate winds. My big dish needs a mount capable
of withstanding over 250,000 foot-pounds in a 50 MPH wind.
You need a well engineered reinforced concrete base to withstand
the forces, and a heavy enough pole to avoid bending under the
load.

BTW, as a source of pipe for the pole, I'm using 6 inch oilfield well
casing, aquired as free scrap from a friend in the business, for my
small dish. The pedestal mount for the larger dish was custom
fabricated by Scientific Atlanta, and came with the dish. There's
7 yards of concrete in the base.

Gary