Back yard tower advice??/
 

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

My question is should i ground that? 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?

Thanks for any advice.

Back yard tower advice??/
 

" Tuuk" wrote in message
...
Hi,
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, this will work great
just screwing them to the wood and it will squeeze itself to the brackets
and support nicely. 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.

My question is should i ground that? 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?

Thanks for any advice.


Thre can never be too much grounding when it comes to lightning. You want
to bond everything together. That way any near by discharges gets grounded
and all the equipment goes up and down with the dishcharge at the same time.
Voltage does not hirt the equipment ,it is just the differance in the
voltages that does.

I think I would ground the dishes/coax to the tower and then atleast once
more just before it comes into the house. Grounding at the bottom of the
tower would also be good if the coax goes all the way to the ground.

Back yard tower advice??/
 

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

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

My question is should i ground that? 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?

Thanks for any advice.

I would [hah!] try to avoid using lumber. Have you ever played with
Unistrut?

Back yard tower advice??/
 

On 9/25/2011 4:11 PM, dave wrote:
I would [hah!] try to avoid using lumber. Have you ever played with
Unistrut?

Figures.

Several commercial tower sites I used to service used wooden
cross supports between telephone poles. The antennas were
bolted directly to the wood cross pieces.

And no, there was no grounding straps/bonds across the supports.
The only grounds the antennas saw was the "ground window" going
into the building.

Jeff

--
"Everything from Crackers to Coffins"

Back yard tower advice??/
 

"Jeffrey Angus" wrote in message
...
On 9/25/2011 4:11 PM, dave wrote:
I would [hah!] try to avoid using lumber. Have you ever played with
Unistrut?

Figures.

Several commercial tower sites I used to service used wooden
cross supports between telephone poles. The antennas were
bolted directly to the wood cross pieces.

And no, there was no grounding straps/bonds across the supports.
The only grounds the antennas saw was the "ground window" going
into the building.

Jeff

The thing with lumber is that it can hold moisture and cause the tower to
rust where the wood is.
Also if it is treated wood, the chemicals may cause the same thing only
faster.

Back yard tower advice??/
 

On 9/25/2011 6:29 PM, Ralph Mowery wrote:
"Jeffrey wrote in message
Several commercial tower sites I used to service used wooden
cross supports between telephone poles.

The thing with lumber is that it can hold moisture and cause the tower to
rust where the wood is.
Also if it is treated wood, the chemicals may cause the same thing only
faster.

Each cross brace has about a dozen 2" diameter galvanized stubs to
attach the antennas to. They are bolted directly to the cross braces.

All the wood was treated with Creosote just like the poles themselves.
The site was at least 40 years old the last time I was up there in 2005.

The stubs didn't look any worse than the usual stubs bolted to metal
tower assemblies.

Jeff

--
"Everything from Crackers to Coffins"

Back yard tower advice??/
 

"Jeffrey Angus" wrote in message
...
On 9/25/2011 6:29 PM, Ralph Mowery wrote:
"Jeffrey wrote in message
Several commercial tower sites I used to service used wooden
cross supports between telephone poles.

The thing with lumber is that it can hold moisture and cause the tower to
rust where the wood is.
Also if it is treated wood, the chemicals may cause the same thing only
faster.

Each cross brace has about a dozen 2" diameter galvanized stubs to
attach the antennas to. They are bolted directly to the cross braces.

All the wood was treated with Creosote just like the poles themselves.
The site was at least 40 years old the last time I was up there in 2005.

The stubs didn't look any worse than the usual stubs bolted to metal
tower assemblies.

I think Creosote is mostly a form of oil. Probalby helps iron not to rust.

The newer treated wood needs special screws depending on the chemicals used.
Thank the EPA for that.

Back yard tower advice??/
 

On Sun, 25 Sep 2011 18:24:01 -0500, Jeffrey Angus wrote:

On 9/25/2011 4:11 PM, dave wrote:
I would [hah!] try to avoid using lumber. Have you ever played with
Unistrut?

Figures.

Several commercial tower sites I used to service used wooden cross
supports between telephone poles. The antennas were bolted directly to
the wood cross pieces.

And no, there was no grounding straps/bonds across the supports. The
only grounds the antennas saw was the "ground window" going into the
building.

Jeff

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?

Back yard tower advice??/
 

On Sun, 25 Sep 2011 18:46:17 -0500, Jeffrey Angus
wrote:

Each cross brace has about a dozen 2" diameter galvanized stubs to
attach the antennas to. They are bolted directly to the cross braces.

All the wood was treated with Creosote just like the poles themselves.
The site was at least 40 years old the last time I was up there in 2005.

You mean like this?
http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/LoopMtn02.html
http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/LoopMtn03.html
We had similar derrangements at 3-4 other sites. Telephone poles and
lumber were about 20% of the cost of a galvanized steel tower.

Lightning protection was at the entry point to the building with a
metal plate with some PolyPhasor feed through protectors. The end and
highest antennas were also grounded with a undersized #4 copper wire
running down the pole to a ground rod at the base. We didn't get any
lightning hits because there was an all metal forestry lookout at the
highest point on Santiago which took all the hits.

The stubs didn't look any worse than the usual stubs bolted to metal
tower assemblies.

We used the same hardware that was used the Ma Bell. Thick galvanized
and loose fitting steel hardware. Same as what the typical steel
tower is made from these days. It works nicely on both metal and
telephone poles.


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

Back yard tower advice??/
 

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

Back yard tower advice??/
 

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

Back yard tower advice??/
 

On 9/25/2011 9:06 PM, Jeff Liebermann wrote:
On Sun, 25 Sep 2011 18:46:17 -0500, Jeffrey
wrote:

Each cross brace has about a dozen 2" diameter galvanized stubs to
attach the antennas to. They are bolted directly to the cross braces.

All the wood was treated with Creosote just like the poles themselves.
The site was at least 40 years old the last time I was up there in 2005.

You mean like this?
http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/LoopMtn02.html
http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/LoopMtn03.html
We had similar derrangements at 3-4 other sites. Telephone poles and
lumber were about 20% of the cost of a galvanized steel tower.

Been on Loop Mountain too. And Oat, Lukens and Mt. Wilson.
The "tower" I was referring to specifically though was Hollywood
Hills.

Lightning protection was at the entry point to the building with a
metal plate with some PolyPhasor feed through protectors. The end and
highest antennas were also grounded with a undersized #4 copper wire
running down the pole to a ground rod at the base. We didn't get any
lightning hits because there was an all metal forestry lookout at the
highest point on Santiago which took all the hits.

The grounding inside and outside the building was your typical "Amateur"
installation. 3/4" water pipe with 90 degree elbows soldered together.

Our real protection was the water tank owned by the DWP slightly up
the hill from us. Similar to ranger tower protecting Santiago.

The stubs didn't look any worse than the usual stubs bolted to metal
tower assemblies.

We used the same hardware that was used the Ma Bell. Thick galvanized
and loose fitting steel hardware. Same as what the typical steel
tower is made from these days. It works nicely on both metal and
telephone poles.

Yup. Works moderately well until you get some clown in the building
that runs an 8-way receive antenna and 8 bandit taxi cab repeaters.

Jeff

--
"Everything from Crackers to Coffins"

Back yard tower advice??/
 

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"

Back yard tower advice??/
 

On Sun, 25 Sep 2011 22:11:11 -0500, Jeffrey Angus
wrote:

http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/LoopMtn02.html
http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/LoopMtn03.html

Been on Loop Mountain too. And Oat, Lukens and Mt. Wilson.
The "tower" I was referring to specifically though was Hollywood
Hills.

There were plenty of telephone pole antenna "towers" in the Hollywood
Hills during the 1960's and 70's. Most are probably still there. A
steel tower required an elaborate ordeal process compliments of the
planning department. Telephone poles were deemed to be something akin
to a tree, and were easier to permit.

During the 1960's, Ken Sessions (SK) had a GE outdoor box mounted on
top of a telephone pole just below Loop Mountain. His problem wasn't
lightning hits. It was hits from .22, .38, and larger. He reinforced
the inside of the box with armor plate, which worked until someone
used AP ammunition. We offered him cheap space in Gene Clothier's
site on Loop, but Ken refused for some unknown reason.

The grounding inside and outside the building was your typical "Amateur"
installation. 3/4" water pipe with 90 degree elbows soldered together.

Lousy cross sectional area. Hopefully, they left one end open. If
the copper pipe were sealed at both ends, and it took a lightning hit,
the air inside would get rapidly very hot and probably turn the pipe
into a fragmentation bomb. If they really want to blow out the wall,
fill it with water.

Our real protection was the water tank owned by the DWP slightly up
the hill from us. Similar to ranger tower protecting Santiago.

Bowmont water tank, off Mullholland between Laurel and Coldwater
Canyons?


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

Back yard tower advice??/
 

On 9/25/2011 10:53 PM, Jeff Liebermann wrote:
On Sun, 25 Sep 2011 Jeffrey wrote:
The grounding inside and outside the building was your typical "Amateur"
installation. 3/4" water pipe with 90 degree elbows soldered together.

Lousy cross sectional area. Hopefully, they left one end open. If
the copper pipe were sealed at both ends, and it took a lightning hit,
the air inside would get rapidly very hot and probably turn the pipe
into a fragmentation bomb. If they really want to blow out the wall,
fill it with water.

Of course the end wasn't open. And there was a pair of Tee's in
the middle so it could zig zag across the ceiling. There was a
second ground pipe running around the outside of the building.

Other sites had a decent ground using #4 solid copper wire and
exothermic connectors. This, obviously, was not one of them.

Our real protection was the water tank owned by the DWP slightly up
the hill from us. Similar to ranger tower protecting Santiago.

Bowmont water tank, off Mullholland between Laurel and Coldwater
Canyons?

I don't think so. This one was off of Cyprean Dr. Via Hollywood Blvd.
http://g.co/maps/dw5py 2050 CYPREAN DR. LOS ANGELES, CA

If that link works properly, you can see a nice clear picture of the
antenna rack.

Jeff-1.0

--
"Everything from Crackers to Coffins"

Back yard tower advice??/
 

On Sun, 25 Sep 2011 20:53:24 -0700, Jeff Liebermann wrote:

On Sun, 25 Sep 2011 22:11:11 -0500, Jeffrey Angus
wrote:

http://802.11junk.com/jeffl/pics/Old...eaters/slides/
LoopMtn02.html
http://802.11junk.com/jeffl/pics/Old...eaters/slides/
LoopMtn03.html

Been on Loop Mountain too. And Oat, Lukens and Mt. Wilson. The "tower" I
was referring to specifically though was Hollywood Hills.

There were plenty of telephone pole antenna "towers" in the Hollywood
Hills during the 1960's and 70's. Most are probably still there. A
steel tower required an elaborate ordeal process compliments of the
planning department. Telephone poles were deemed to be something akin
to a tree, and were easier to permit.

During the 1960's, Ken Sessions (SK) had a GE outdoor box mounted on top
of a telephone pole just below Loop Mountain. His problem wasn't
lightning hits. It was hits from .22, .38, and larger. He reinforced
the inside of the box with armor plate, which worked until someone used
AP ammunition. We offered him cheap space in Gene Clothier's site on
Loop, but Ken refused for some unknown reason.

The grounding inside and outside the building was your typical "Amateur"
installation. 3/4" water pipe with 90 degree elbows soldered together.

Lousy cross sectional area. Hopefully, they left one end open. If the
copper pipe were sealed at both ends, and it took a lightning hit, the
air inside would get rapidly very hot and probably turn the pipe into a
fragmentation bomb. If they really want to blow out the wall, fill it
with water.

Our real protection was the water tank owned by the DWP slightly up the
hill from us. Similar to ranger tower protecting Santiago.

Bowmont water tank, off Mullholland between Laurel and Coldwater
Canyons?

K-Joy site? You must know Western Technical Services if you used to play
in Orange County. They build steel towers. If you order a mesh dish they
send an unmarked vehicle.

Back yard tower advice??/
 

On Mon, 26 Sep 2011 07:59:44 -0500, dave wrote:

K-Joy site? You must know Western Technical Services if you used to play
in Orange County. They build steel towers. If you order a mesh dish they
send an unmarked vehicle.

Never heard of them, but that was 40 years ago. We did our own
antennas all of which were on wood poles. Same with everyone else on
Santiago Pk in the late 1960's. Even the Air Force building used
multiple short telephone poles, with one antenna per pole, a really
bad idea. I worked for PMC (Pacific Mobile Comm) in Stanton CA at the
time.
http://11junk.com/jeffl/pics/Old%20Repeaters/slides/PMC02.html

Why would they send an unmarked vehicle to install a mesh dish?

I think (not sure) that I found a recent (4/2009) photo of the PMC
building on Santiago:
http://images.summitpost.org/original/503620.jpg
Note the large number of wooden poles and outriggers that are still in
use. I was going to mumble something like "nobody mounts dishes on
wood poles", but it seems that there are two in the photo. Sigh. The
wood structure looks much the same as it did 40 years ago minus the
wall of far too closely spaced, intermod generating, antennas.

Recent structures are all steel.
http://images.summitpost.org/original/503619.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

Back yard tower advice??/
 

On 9/25/2011 7:06 PM, Jeff Liebermann wrote:
The end and
highest antennas were also grounded with a undersized #4 copper wire
running down the pole to a ground rod at the base. We didn't get any
lightning hits because there was an all metal forestry lookout at the
highest point on Santiago which took all the hits.


#4 is plenty big enough for lightning grounding. The current is high,
but the duration is short. You see larger lightning conductors for
mechanical reasons (e.g. where it might get damaged, or where it has to
move repeatedly).

Back yard tower advice??/
 

On Mon, 26 Sep 2011 12:04:21 -0700, Jim Lux
wrote:

On 9/25/2011 7:06 PM, Jeff Liebermann wrote:
The end and
highest antennas were also grounded with a undersized #4 copper wire
running down the pole to a ground rod at the base. We didn't get any
lightning hits because there was an all metal forestry lookout at the
highest point on Santiago which took all the hits.

#4 is plenty big enough for lightning grounding. The current is high,
but the duration is short. You see larger lightning conductors for
mechanical reasons (e.g. where it might get damaged, or where it has to
move repeatedly).

One of the neighboring towers took a direct hit. The #6 AWG he was
using literally exploded, spraying melted copper everywhere and
blowing pieces of concrete block all over the building.

http://en.wikipedia.org/wiki/American_wire_gauge#Table_of_AWG_wire_sizes
Fusing current (32msec) for #4 is 34,000 Amps. The average lightning
hit is about 20,000A but can go up to 200,000A.
http://www.lightningsafety.com/nlsi_info/media.html
Other references offer averages from 5,000 to 50,000A. I would call
#4 marginal but probably adequate for California, which doesn't get
much lightning.

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

Back yard tower advice??/
 

"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"

Back yard tower advice??/
 

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

Back yard tower advice??/
 

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

Back yard tower advice??/
 

" 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)

Back yard tower advice??/
 

On 9/26/2011 3:45 PM, Jeff Liebermann wrote:
On Mon, 26 Sep 2011 12:04:21 -0700, Jim
wrote:

On 9/25/2011 7:06 PM, Jeff Liebermann wrote:
The end and
highest antennas were also grounded with a undersized #4 copper wire
running down the pole to a ground rod at the base. We didn't get any
lightning hits because there was an all metal forestry lookout at the
highest point on Santiago which took all the hits.

#4 is plenty big enough for lightning grounding. The current is high,
but the duration is short. You see larger lightning conductors for
mechanical reasons (e.g. where it might get damaged, or where it has to
move repeatedly).

One of the neighboring towers took a direct hit. The #6 AWG he was
using literally exploded, spraying melted copper everywhere and
blowing pieces of concrete block all over the building.

http://en.wikipedia.org/wiki/American_wire_gauge#Table_of_AWG_wire_sizes
Fusing current (32msec) for #4 is 34,000 Amps. The average lightning
hit is about 20,000A but can go up to 200,000A.


One might want to check a different source for fusing current. The
standard test lightning stroke has a 2 microsecond rise time (10% to
90%) and a 50 microsecond fall time (to 50%) typically represented by a
double exponential (1-exp(-t/a))*exp(-t/b), so when you used the
Onderdonk equation, you want to use a 50 microsecond pulse

In general, fusing goes as a function of the "action", I^2*time.

The equation from Onderdonk is usually used for this kind of thing (as
shown in the table you cited). Onderdonk's equation assumes a
rectangular current pulse, but that works for the most part and for
lightning, it would be a conservative estimate.

For a 50 microsecond pulse, the fusing current is 22 amps/cmil (vs .87
A/cmil for the 32 ms pulse)

AWG4 is 42kcmil, roughly, so the fusing current is well over 8000kA

Another approach to analysis might be to consider the energy dissipated
in that wire. It's a bit tricky, because as the wire heats up, the
resistance increases. (by a factor of 4 or 5 at the melting point, as I
recall)

But let's consider a meter of that wire which is 5.189mm in diameter.
it has a resistance of 0.82 milliohm (at 25C). Let's round up to 5
milliohms.

Let's say our lightning stroke has an RMS current of 50kA (peak current
would be higher), so we have (50E3)^2*5E-3 = 12.5 MW. But that lasts
for only 50E-6 seconds, so we deposit 12.5E6*50E-6 = 625 Joules into the
meter of wire.

That wire has 21 sq mm cross section so the one meter length is about
21E-6 cubic meters or 21 cc. Copper has density about 7 g/cc, so we've
got around 150 grams of copper there. At a specific heat of 0.385 J/g
every 58 Joules will raise the temperature 1 degree. Since we're
dumping in about 600 joules, that lightning stroke will raise the
temperature around 10 degrees.

In practice, a typical lightning strike has several strokes, so you
probably dump 4-6 times that amount of energy into the wire. But still,
you're talking maybe a 50-60 C temperature rise, which is LONG way from
the 1000 degree rise you need to melt the copper.


Your observation of total destruction of a copper conductor was probably
from some other mechanism. The electromagnetic forces are the best
candidate. I used to do some quarter shrinking, and a few thousand amps
in sub millisecond pulse would destroy a AWG10 coil from the magnetic
forces.

An unsupported turn of AWG 4 or 6 wire would probably be destroyed by a
20kA pulse with a rise time of 2 microseconds. The di/dt is 400E9 A/sec,
so the flux is pretty spectacular.

The other source of disaster in high power pulse discharges is if there
is a loose connection or a gap in the conductor. The several tens of
volt cathode drop in an arc at 20kA gets the peak power up pretty high,
and unlike in the example above where the 12MW is distributed over a
meter of length, you get that megawatt dissipated in a few cm, so the
energy density is much higher.


http://www.lightningsafety.com/nlsi_info/media.html
Other references offer averages from 5,000 to 50,000A. I would call
#4 marginal but probably adequate for California, which doesn't get
much lightning.

Back yard tower advice??/
 

On 9/27/2011 1:10 PM, Sal wrote:
" 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.



Typical optos can stand off 5kV or so. Speed is a problem There are off
the shelf opto isolator widgets for things like RS232 and phone lines
that are fairly inexpensive. Get to RF, though, and the price goes way up.

If you need more, you go to a fiber optic link of some sort.

Back yard tower advice??/
 

On Tue, 27 Sep 2011 13:10:30 -0700, Sal wrote:

" 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)

These fine folks make a heavy duty 75 Ohm protector:

http://www.alphadeltacom.com/

Back yard tower advice??/
 

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

Back yard tower advice??/
 

On Sep 25, 7:46*pm, Jeffrey Angus wrote:
On 9/25/2011 6:29 PM, Ralph Mowery wrote:

"Jeffrey *wrote in message
Several commercial tower sites I used to service used wooden
cross supports between telephone poles.

The thing with lumber is that it can hold moisture and cause the tower to
rust where the wood is.
Also if it is treated wood, the chemicals may cause the same thing only
faster.

Each cross brace has about a dozen 2" diameter galvanized stubs to
attach the antennas to. They are bolted directly to the cross braces.

All the wood was treated with Creosote just like the poles themselves.
The site was at least 40 years old the last time I was up there in 2005.

The stubs didn't look any worse than the usual stubs bolted to metal
tower assemblies.

Jeff

--
"Everything from Crackers to Coffins"

Same here Jeff, creosote poles and cross arms 30 years old with hot
dipped galvanized hardware. No sign of deterioration.

Jimmie

Back yard tower advice??/
 

On Tue, 27 Sep 2011 20:32:28 -0700, JIMMIE wrote:

On Sep 25, 7:46Â*pm, Jeffrey Angus wrote:
On 9/25/2011 6:29 PM, Ralph Mowery wrote:

"Jeffrey Â*wrote in message
Several commercial tower sites I used to service used wooden cross
supports between telephone poles.

The thing with lumber is that it can hold moisture and cause the
tower to rust where the wood is.
Also if it is treated wood, the chemicals may cause the same thing
only faster.

Each cross brace has about a dozen 2" diameter galvanized stubs to
attach the antennas to. They are bolted directly to the cross braces.

All the wood was treated with Creosote just like the poles themselves.
The site was at least 40 years old the last time I was up there in
2005.

The stubs didn't look any worse than the usual stubs bolted to metal
tower assemblies.


Same here Jeff, creosote poles and cross arms 30 years old with hot
dipped galvanized hardware. No sign of deterioration.

Jimmie

Ask John Franklin in Santa Barbara how his telephone poles are doing on
Gibraltar these days...