Q on grounding for cell phone antenna

[Mamba]

I am installing a cellphone antenna at a country cabin. The cabin has a steep "A" frame roof (metal) with dormers that stick out about 10' below the peak. In addition, the cabin has metal siding all around the base, to a height of about 12'.

I will install a vertical pole at the end of one of the dormers, with a 30" Yagi cell phone antenna mounted on it. The pole will be attached to the side of the dormer, with clamps screwed into the side of the facia and trim boards, and will rise about 3' over the roofing of the dormer (also metal). The antenna height will still be 7 or 8 feet below the peak of the roof. Coax will run from the antenna to a signal booster inside the cabin.

While looking at the antenna installation instructions, I noted that grounding is recommended for all installations. Trying to determine the best way to do this, or if it is necessary at all. The cabin is in a canyon in WA state. Lightning is a rarity, it's in a canyon about 200' below adjacent ridge, and the metal roof of the cabin is a lot higher than the antenna.... I anticipate using a wooden pole for the mounting of the antenna, if that has bearing as well.

Q's on this project:

1. Is wooden pole optimal? Would metal or fiberglass be better? I only need to elevate the antenna about 3' off the dormer. I was avoiding metal because I thought it would generate further grounding issues. The protected location makes wind a non-factor for pole material choice - i.e. doesn't need to withstand high winds.

1. If I do run a ground wire, it would have to run down the side of the cabin to (I presume) a big metal rod in the ground. The wire itself would have to be attached to the side of the cabin, which is also metal. Would this be just increasing a risk of electrifying the place if a strike was to occur? Or would the wire need to be held away (via insulating material?) from the metal siding?

Advice appreciated.

[trader4]

Normally antennas like this come with a u-bolt clamp intended to be fastened to a metal pole. That pole is then part of the ground system and connected to the ground wire. That's how I would do it.

I only

It doesn't.

The protected

I would think running the ground wire to a proper ground rod along the outside metal siding would not be a problem. If the antenna takes a strike, the path of least resistance is going to be straight down the ground wire. And you already have the possibility of a lightning strike hitting the metal roof or siding right now, with or without the antenna. I don't see insulators doing you any good. A lightning strike is huge volts/amps. Any reasonable insulator, even a dry one let alone one exposed and wet, is going to be easily overcome. You should minimize the bends/turns in the ground wire. And the cable should have a grounded lightning arrestor connected to it where it enters the building.

[John McGaw]

At the very least you will want to have a grounding block connected to a proper earth ground as close to the building entry point as possible. Depending on what sort of coax you are using a block such as used for satellite antenna or cable TV may be suitable (and cheap). Otherwise you may have to hunt for a suitable block but you _really_ do need one. If you do have any sort of an insurance claim that might be even vaguely related to the antenna installation you can be sure that the insurance company's investigator will be looking for one.

[Mamba]

This posting gives me pause. The coax I have purchased is a special ultra-low loss 20' length with special proprietary connectors for the antenna and the cell phone amp at each end. I would need to cut it to add generic connectors at both sides of a grounding block. Darn, I expect the extra noise introduced by adding connections to it would degrade the signal to the point where it would be unusable - the improvement I get with my tests using the antenna just barely gives me enough signal for cell calls.

[tnom]

Just mount the yagi on a metal mast and run a clamped on wire from the bottom of the mast down to a rod driven into the ground. If you want to use a wooden mast then just clamp a wire to the boom or the mount of the antenna and run the wire perpendicular to the boom and away from the antenna down the wooden mast. The ground driven rod is ideally eight foot long but it is unlikely you'll be able to use the full length. If possible drive the ground rod close to grounded plumbing like your outside water spigot. Attach a short jumper to the plumbing also.

[hallerb]

connect ground wire to main house ground if there is one, or install ground rod, and run ground wire from antenna to new ground rod and main house ground and plumbing, assuming outdoor plumbing is metal

[hallerb]

i would NOT mess with the ultra low loss coax under any circumstance!

[Bob M.]

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.

[hallerb]

OP can add a amplifier too for greater range and power..........

[Mamba]

This is the ticket. I'll do it this way. Best compromise between safety and signal quality.

Couple of more questions then....

I'll be running the wire down the outside of the house, over metal siding. Will need to bolt/clamp it to the side of the house since it will be a 10' + run. Do I need special clamps to try to keep the wire off the wall?

Also, what gauge wire is recommended? Is there a special designation for grounding wire that the folks at the supply store will know (and obviously I don't).

Thanks again

[trader4]

Not according to the NEC, which requires an arrestor on the cable and doesn't have a compromise. What you are proposing grounds the antenna mast, but leaves the antenna itself with no protection. If there were even a nearby lightning strike, the antenna could wind up with thousands of volts and that energy is going to go down the coax and into your cell phone.

Every outside antenna installation picture from manuals and similar I've ever seen shows both grounding the mast and using an arrestor on the cable where it enters the building. Did you look in the instructions for the antenna you have?

[hallerb]

se between safety

look for practical purposes its impossible to ground a yagi cell antenna properly unless you can find a grounding block designed specifically for cell phone antennas, I have never seen one =2E not only that but keeping the ground wire away from the metal siding is meaningless too.

a nearby lightning strike will electrify everything, and fry all the electronics too.

sometimes there just so much you can do. I wouldnt recommend taking on the cell phone during a electrical storm, I would unplug the phone from the antenna.

but you should never talk on a regular phone during lightning either.

[trader4]

mise between safety

=BD =EF=BF=BDIf

Just because you have never seen one doesn't make violating NEC and not using an arrestor OK. I'm sure suitable arrestors exist. Also there are a variety of adaptors that can adapt various coax to various connectors.

That I agree with.

It likely will if the antenna is not properly grounded or there is no arrestor on the cable. Otherwise, if the antenna, power, utilities, etc are properly grounded and protected, it's unlikely a nearby stike will electrify everything and fry all the electronics inside a house.

That still leaves the antenna high on the roof with a cable with no arrestor going into your house. You may be OK with that, but the NEC isn't. Also, I'm not sure what an insurance company might do come claim time if the house was burned down from a lightning strike attributable to a homeowner install that clealy violates NEC.

e quoted text -

[tnom]

Wrong. A Yagi by design is DC grounded. Boom and elements.

[Jim Yanik]

[e-mail] wrote in news: [e-mail]:

but is what the Yagi *mounted on* grounded? (not the cable shield,a REAL ground.) if you bolt an antenna tripod or chimney mount on your roof,they will need a proper ground wire.

just depending on a cable "ground" will channel lightning into your receiver and home.

[trader4]

Show me where in the NEC code it says that no arrestor is required on a Yagi like the OP is proposing to install.

Every antenna install sheet I've ever seen requires it, as done NEC.

[tnom]

Didn't what I said aboveground the mast or boom?

[tnom]

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.

[Jim Yanik]

[e-mail] wrote in news: [e-mail]:

Not necessarily. Uninformed homeowners might not know to ground the mast/boom/antenna mount,or figure they can get by without it.

[tnom]

snip

Grounding just the mast would automatically ground the whole system regardless of a home owners understanding of the system. Why? Because the boom, mount, coax outer shield, and mast are all electrically the same. Grounding the mast as I stated, would automatically ground everything. It's dummy proof.