On Sun, 25 Sep 2011 09:45:19 -0400, " Tuuk" wrote:

I have a big self supporting tower in the yard, it is grounded by grounding
rods and of course itself. I am attaching two satelite dishes to the tower.
The most practical way is using 2x4 wood,

It won't work. The problem is that wood towers move. If the
satellite dish just happens to have a very narrow beamwidth, such as
with a point to point link or DBS dish, that movement is going to
misalign the dish. I had a (non-paying) customer with such a
derrangement. Instead of a steel pipe and concrete filled hole
mounting as recommended, he installed it on top of a 20ft 4x4. I was
asked to align the dish properly, which turned into a exercise in
futility. The wood was still fairly green. Every time the sun shined
on one side of the 4x4, it would contract on that side only. I bought
a MEMS inclinometer and setup a laser pointer to measure the changes.
My guess is about a 3 degree max change at the top. Note that the
beamwidth of the common 24dBi 2.4Ghz dish is about 5 degrees, which
means you have to be accurate to at least +/- 2.5 degrees.

this will work great just screwing
them to the wood and it will squeeze itself to the brackets and support
nicely.

Using a piece of 2x4 as a yard arm will probably not produce as
drastic a change. It will be somewhat less, but it will still be
present. In addition, you'll have the never ending problem of
securing the 2x4 properly with bolts. As the wood dries out, you'll
be tightening the bolts, and re-tweaking the dish alignment.

I am wondering about the connection to the tower because there will
not be grounded to the tower. There wont be any connection (metal to metal)
form the satelite dish and the tower, that leads me to believe that the only
grounding would be the shielded cable which gets grounded to the nice new
50" plazma.

OK, it's a DBS dish. The typical 18" pizza dish has a beam width of
about 4 degrees. If it's a multiple LNB dish as used to get HDTV
channels, about 3 degrees. That means you'll need to be accurate to
about +/- 1.5 degrees. Wood won't work.

It will also be rather amusing to watch you try to align a dish to 1.5
degrees accuracy at the end of the 2x4. The usual method of
pre-setting the elevation, and spinning the dish for max signal to get
the azimuth will work only if the mounting pipe is absolutely
vertical. That's not easy to do or adjust with a 2x4 hanging out away
from the tower.

My question is should i ground that?

Running a heavy copper wire up the tower and across the 2x4 might be a
problem. That's because of the right angle turn at the tower.
Lightning doesn't like to make right angle turns and will probably
jump to the tower. I don't really know if this should be a concern.

The local DBS installers just use a #10 copper wire to the nearest
earth ground. The cable guys just ground the F connector at the
building entry. They're not really designed to take a lightning hit,
just to bleed off any static electricity that might accumulate or to
deal with an indirect hit.

Should the satelite dish itself be
grounded to the tower? Is there any reason for this? Safety wise or
interference wise? It would be very simple to do, but not sure if I should
or want to. Please give me advice as to either ground the dish to tower or
not to. Does anyone think there will be issues? Should I or shouldn't I?

Well, if you're going to go through all that trouble to install a
proper ground, you can do as well using Unistrut instead of a 2x4.
http://www.unistrut.us

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558