On Sun, 25 Sep 2011 20:28:15 -0500, dave wrote:

I'm not sure I'd want to hang a TVRO dish on one. Have you ever been on
the upper levels inside the Post Office building on Mt. Wilson?

http://www.cellsiteanalysis.net/cell_site_analysis_images/Cell_Site_Mast_Loaded.jpg
(It's not Mt Wilson. It's in Turin Italy).

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

On 9/25/2011 8:28 PM, dave wrote:
I'm not sure I'd want to hang a TVRO dish on one. Have you ever been on
the upper levels inside the Post Office building on Mt. Wilson?

As the other Jeff pointed out, there's reasons to NOT use wood,
but it's not because wood is bad. Purely a dimensional change
problem.

Although, I suspect that the original poster is thinking of
strapping a 2x4 across two legs of the tower and using just enough
"arm" to get the dish to clear the tower. It may work, and it may
be a nightmare trying to accurately align it.

Jeff


--
"Everything from Crackers to Coffins"

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

"Jeff Liebermann" wrote in message
...

snip


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

Unistrut is wonderful. About 20 years ago, I used to engineer installations
in a big government lab in San Diego and it was the customer's preferred
method for anything structural that didn't involve concrete. :-)

I learned you could do anything with Unistrut. It's the Erector Set / Lego
Blocks for grown-up kids.

"Sal"

On Mon, 26 Sep 2011 22:08:23 -0700, "Sal" wrote:

"Jeff Liebermann" wrote in message
.. .
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

Unistrut is wonderful. About 20 years ago, I used to engineer installations
in a big government lab in San Diego and it was the customer's preferred
method for anything structural that didn't involve concrete. :-)

I learned you could do anything with Unistrut. It's the Erector Set / Lego
Blocks for grown-up kids.

"Sal"

Agreed. However, you have to be careful using Unistrut for outriggers
on towers. Unistrut doesn't do well when twisted (in torsion) by a
top heavy antenna. The only way that seems to work well on a tower
are two 1 1/2" channel Unistrut outriggers, with a connecting pipe for
mounting the antenna, dish, or whatever. A single outrigger usually
results in a the antenna twisting around in the wind. (1 1/4" will
work with light antennas).

Something like this:
http://i668.photobucket.com/albums/vv44/ahwwwjeah/My%20Tower/DSCF6120.jpg
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Thanks for all the info

I am going to ground out the satellite dish to the tower.

Now it is grounded to my new plazma and I would feel more comfortable with
it grounded to the tower. Don't want nothing happening to that new plazma.
Now of course if it ever got hit by lightning I would imagine the receiver
would get fried, maybe not the tv, the coax goes into the receiver, then
into the yamaha sourround sound then into the tv. A jolt has to stop
somewhere along that line.





"Jeff Liebermann" wrote in message
...
On Mon, 26 Sep 2011 22:08:23 -0700, "Sal" wrote:

"Jeff Liebermann" wrote in message
. ..
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

Unistrut is wonderful. About 20 years ago, I used to engineer
installations
in a big government lab in San Diego and it was the customer's preferred
method for anything structural that didn't involve concrete. :-)

I learned you could do anything with Unistrut. It's the Erector Set /
Lego
Blocks for grown-up kids.

"Sal"

Agreed. However, you have to be careful using Unistrut for outriggers
on towers. Unistrut doesn't do well when twisted (in torsion) by a
top heavy antenna. The only way that seems to work well on a tower
are two 1 1/2" channel Unistrut outriggers, with a connecting pipe for
mounting the antenna, dish, or whatever. A single outrigger usually
results in a the antenna twisting around in the wind. (1 1/4" will
work with light antennas).

Something like this:
http://i668.photobucket.com/albums/vv44/ahwwwjeah/My%20Tower/DSCF6120.jpg
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

" Tuuk" wrote in message
...
Thanks for all the info

I am going to ground out the satellite dish to the tower.

Now it is grounded to my new plazma and I would feel more comfortable with
it grounded to the tower. Don't want nothing happening to that new plazma.
Now of course if it ever got hit by lightning I would imagine the receiver
would get fried, maybe not the tv, the coax goes into the receiver, then
into the yamaha sourround sound then into the tv. A jolt has to stop
somewhere along that line.

I know what an opto-isolator is. (Provides a signal path with a short-range
modulated light beam -- no copper connection) I don't know if any have been
designed/sold for lightning protection.

Anybody?

"Sal"
(KD6VKW)

On Tue, 27 Sep 2011 07:53:06 -0400, " Tuuk" wrote:

Thanks for all the info

Y'er welcome. Now, if you want a usable answer to your question, it
might be helpful if you describe the tower, what manner of DBS dish,
and some of the distances involved.

I am going to ground out the satellite dish to the tower.

If your unspecified type of tower is properly grounded, the tower will
protect the dish from a direct hit. Still, it's a good idea to ground
everything to reduce the effects of induced currents from a nearby
hit.

Grounding the dish is probably a good idea. Grounding the LNB at the
dish is a bad idea. Depending on model of LNB, many of them have no
DC connection between the LNB case and the dish ground. This is not
for lightning protection but to prevent ground loops. In general, you
want to do it the way the installation manual suggests and the NEC
electrical code demands, which is a grounded barrel connector
somewhere close to the utilities ground.
http://www.dbsinstall.com/whatis/Whatisgood-5.asp
Such a ground is NOT to protect against lightning, but to protect
against getting electrocuted if the satellite receiver magically loses
its protective AC ground and leaks some 117VAC onto the coax.

This discussion has some good comments on DBS dish grounding.
http://www.dbstalk.com/showthread.php?t=16300

Now it is grounded to my new plazma and I would feel more comfortable with
it grounded to the tower. Don't want nothing happening to that new plazma.
Now of course if it ever got hit by lightning I would imagine the receiver
would get fried, maybe not the tv, the coax goes into the receiver, then
into the yamaha sourround sound then into the tv. A jolt has to stop
somewhere along that line.

The general idea is to give the current a better path to ground than
through your expensive electronics.

Incidentally, I just found this on using wood for mounting:
http://www.dbsinstall.com/diy/GroundPostInstallation.asp

What's inside a Polyphaser cellular lightning protector:
http://802.11junk.com/jeffl/pics/lightning/index.html
Note the 4 ceramic spark gaps in series. You get 4 hits, and then it
shorts out.

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