On Tue, 20 Nov 2007 15:54:02 -0800 (PST), firstname.lastname@example.org wrote:
A lightning arrestor is different than grounding the antenna.
Grounding the antenna may stop a house fire from starting. That is
the idea. It's suppose to direct a lightning strike to ground without
going through your house. It may or may not do this. There is no
Grounding is also suppose to drain static to the ground an possibly
stop noise on a receiver.
Grounding will also reduce surge currents from going down the
coax center lead and damaging your electronics if a lightning strike
hits near your installation but misses it. An arrestor is inline with
the coax center conductor and shunts the same surge current to the
outer conductor during a near miss lightning strike.
No amount of arresting or grounding will protect the receiver or
amplifier with a direct hit. If you get a direct hit you'll be tossing
the electronics into the trash. The best scenario during a direct hit
is to just protect the house from starting on fire. That can be
accomplished with grounding, not arresting.
The route for a grounding wire in this application is somewhat complex. The
dormer described sticks out from the bottom of the "A" roofline about 12'
off of grade, so a ground wire from the mast would need to follow down the
outline of the dormer wall, back about 4' to the exterior wall (with metal
siding), then down vertically about 12 to a grounding rod.
As I understand it, non-vertical ground wires are less effective than
straight runs down. Curious to know if I could simply ground the mast to
the metal siding, and have a short grounding wire from the bottom of the
metal siding to the grounding rod? Use the siding as part of the ground?
Get Motorola's R-56 Standards book.
It describes proper installation and grounding methods for
Using your siding as a component of the grounding system is
NOT a good idea.
The way I would do it is to connect up your antenna using
say 1/4" superflex, use a transmission line outer ground sheathing
kit, bond that ground to an external ground bus bar, also ground
to that bus bar, your Polyphaser (lightning arrestor), then use a
cadwelded ground cable from the bus bar to a ground rod (or site
perimeter ground - your main AC & telco grounds should also be
connected to that same point). You will have to pay for the "N"
connectors and superflex to use, as well as the copper bus bar.
It's more expensive than a typical "ham" or scanner enthusiast
setup. If you really want to go all out, get 7/16" DIN connectors
to alleviate passive intermod issues (or so they say).
That is the proper "industry standard" way of accomplishing the
grounding of a communications antenna.
Install it to the standards of the cellular companies and
mission critical communication sites, and you'll be fine.
May cost a bit more upfront, but it'll be done right. I've
had several of my sites take direct lightning hits in lightning
alley (FL), and the communication systems kept on working
without missing a beat. Some Polyphasers became high Z after
the hit, setting off VSWR alarms, but the on call techs got
to the site and replaced them, and the equipment was fine.
(mind you this is a multi million $$ site built from the
ground up with lightning protection in mind).
I suspect it is against electrical code to use the siding as a "ground"
in ANY manner,and a superlatively DUMB move.
there's no guarantee that each siding panel(being painted or coated!!) is
connected electrically to the adjacent panels,and there's a VERY good
chance of corrosion or high resistance,negating any grounding ability.
Most likely,any lightning strike would jump over to the nearest electrical
wiring inside the walls,or any nearby metal plumbing.
and burn down your home.
Some do float, but that would be rare. Assuming it floats the driven
element on a cell phone director is how long? It is barely a target.
If the structure around it is grounded (boom,mount ect.)then the
antenna is mostly protected in as much as you can actually protect it
Your metal roof and siding may actually get in the way. I'm not talking
lightning here, but cell phone signals. They may bounce them all over the
place. Look up ham radio sites related to yagi antennas in the 800-1000 mHz
range. Also, any leafy trees nearby? They're RF sponges.
Hopefully you're not trying to hook up to an analog system. The FCC has
given the OK to cell co's to turn off analog systems on 2/18/08. They're not
required to, just allowed to.
Wrong place for the booster. It'll boost signal Plus any noise induced
by coax and connectors. Shop for an antenna with built-in booster.
They're typically powered by 12 volts dc applied to the coax from
your 'cabin' end of the run. (The single piece of coax carries the
DC power to the antenna-mounted amplifier as well as the signal
from the antenna).
You might expriment with raising the antenna above the metal
roof for best signal strength.
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