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Roof Top Antenna

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WQOQ867

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Im looking to mount a 48 inch fiberglass VHF antenna on my roof atop my tv antenna post.

Will it need to be grounded for lightning?
 

12dbsinad

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Yes, it should be grounded. Usually most commercial fiberglass antenna's are DC grounded through the support pipe, so grounding the support structure would be the way to go.
 

mmckenna

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As 12db said, yes.

National Electric code requires it. If you have any sort of home owners insurance that you would want to use at any point, you need to make sure your install meets the National Electric Code requirements.

That means it needs to be grounded per code.
Support structure needs to be grounded, straight down to a ground rod giving the easy path for lightning. That also needs to be bonded to the same ground as your homes electrical system.
In addition:
Coax shield grounded to the mast near the antenna.
Coax Shield grounded before it enters the home.
You'll also want a product like a Polyphaser where the coax enters the house.

Direct lightning strikes are not the only concern. Even a nearby strike can induce enough energy in the antenna or feedline to cause damage.

Might sound like a lot of work, but using the right materials for the job, such as grounding kits designed for the exact coax you are using, having the right connectors on everything, etc. makes it easy. If you can mount the antenna near your existing electric meter, you should have a ground rod there. That'll make interconnecting everything easier.
 

WQOQ867

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ok, thank you. I have a pole off the side of the house (about 20 feet away), its metal straight into the ground. Used to be used for a dish, if i mount it on there and run my coax under ground to the house will i still need to meet national electric code? The antenna should ground being attached to a pole that goes right into the ground correct? Its not as high but i sit on top of a big hill looking into town were I'm looking to transmit to.
 

lmrtek

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You should drive in a ground rod and bond it to the pipe.

And you should install a lightning arrestor on the coax where it enters the house

Buried coax still isn't grounded and it becomes a perfect path for lightning to travel into the house.
 

mmckenna

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ok, thank you. I have a pole off the side of the house (about 20 feet away), its metal straight into the ground. Used to be used for a dish, if i mount it on there and run my coax under ground to the house will i still need to meet national electric code? The antenna should ground being attached to a pole that goes right into the ground correct? Its not as high but i sit on top of a big hill looking into town were I'm looking to transmit to.

No, it's not suitable for grounding.

The support structure needs to be properly grounded. A random amount of galvanized mast in the ground or in concrete isn't suitable. You need to have a ground rod near the base and properly connected to the mast.
That ground rod needs to be bonded to the house system. All your grounds need to be connected or you can get a difference in potential, and that's a bad thing

Cable underground isn't safe. All that energy hitting the ground will dissipate, but not before finding various paths. That would include your cable. I've had it happen at work. Back in the early 90's we had a strike hit the ground. It induced enough energy into a copper cable to blow out a terminal server system that fed multiple buildings.

Your install has to meet NEC. If it doesn't, you might get away with it. In the event of a strike, or even nearby strike, that does any damage to your home, the insurance company is going to look for ways that would result in them not having to pay out on your claim.

It's your house, your radio, your cable, your insurance policy. The decision is up to you. If you like to gamble, then have at it. If you want to do it right, NEC.
 
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