Q on grounding for cell phone antenna

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On Tue, 20 Nov 2007 15:54:02 -0800 (PST), snipped-for-privacy@optonline.net 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 guarantee.
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.
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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?
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Get Motorola's R-56 Standards book.
It describes proper installation and grounding methods for communication antennas.
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).
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snip

You are correct about straight runs being better. I don't know if I would use the metal siding as a conductor. Doing that may increase the likelihood of stray current branches entering the house.
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snipped-for-privacy@mucks.net wrote in

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.
--
Jim Yanik
jyanik
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On Tue, 20 Nov 2007 17:05:09 -0500, snipped-for-privacy@mucks.net wrote:

Improper generalization. Directors and reflectors, yes. Driven element(s), not always. I have a tri-band amateur yagi that has a floating driven element.
--
Art Greenberg
artg at eclipse dot net
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wrote:

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 from lightning.
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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.
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OP can add a amplifier too for greater range and power..........
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Mamba wrote:

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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