Antenna Installation Design

[Ravenvalor]

I was wondering, if I were to find a local antenna installer in say a state like North Carolina to install a 20' high TV antenna for me would I have to worry about lightning protection or would the installer be well versed in that part of antenna installation? I currently have an antenna mounted to an old brick chimney that I am taking down so the antenna needs a new home.
Thanks...

 

[gar]

201018-1546 EDT

Ravenvalor:

What is the difference between an antenna on a chimney, and on a tower?

In either case my opinion is you need lightning protection.

20 ft seems like a low tower. I expect your tower may be on some concrete base, or other type of base. That may be adequate earthing of the tower, or you may want to add grounding electrodes. Consider this: your earth resistance tower to remote earth is 10 ohms, low for many areas. A 1000 A lightning bolt hits the tower. 1000 * 10 = 10,000 V. Probably for 10 microseconds. You want very little of this current to actually get into your home, wiring, and TV set and other things.

Ideally you want spark gaps, MOVs, other transient limiters, before a filter going into your home. DC isolation might be good. Practically no one does this. A large gap RF isolation transformer might also help.

Years ago there was a person on the Internet discussing his methods. Long gone. He was in Florida and worked at a TV station.

.

 

[hbiss]

I was wondering, if I were to find a local antenna installer

If you lived where I am 50 years ago that would be me. I was the only game in town for both residential and large commercial systems.

Then cable came along...

-Hal

 

[suemarkp]

DC isolation can be a problem if the antenna requires power because of built in amplification (e.g. GPS antennas, some TV antennas with built in amps). DC power is sent up the coax to provide that power to the antenna. I got tired of swapping antenna lightning arrestors when we had AC ones and someone placed an antenna that meeds DC up the wire. Now I just put in ones that pass DC too.

 

[hbiss]

If the antenna uses coax directly (IOW no 300-75 ohm matching transformer on it) the braid is connected to the antenna so all you need to provide is a grounding block to bond the braid to your GEC where it enters the house. And even if it does use a matching transformer, that's all that's required also.

Don't overthink this.

And it would probably be a good idea to figure on a new antenna. Rarely does anything that's been out in the elements very long survive moving, even the heavy duty commercial ones.

-Hal

 

[suemarkp]

Yes, I've changed to using feed thru connectors on a grounded metal plate for our antenna arrays. The first few installs, people pointed me to EMP and lightning arrestors with the glass capsule inside them. They cost too much money so I stoped using them and we don't have EMP requirements. But good feed thru's aren't cheap either especially the higher frequency ones (4GHz or higher).

 

[hbiss]

Yes, I've changed to using feed thru connectors on a grounded metal plate for our antenna arrays. The first few installs, people pointed me to EMP and lightning arrestors with the glass capsule inside them. They cost too much money so I stoped using them and we don't have EMP requirements. But good feed thru's aren't cheap either especially the higher frequency ones (4GHz or higher).

This is just a TV antenna.

Oh, and I forgot to mention in my post above the ground for the mast. Ground clamp on the mast, #6 as directly as possible down to the GEC also.

-Hal

 

[tom baker]

Rules for antennas are in art 810
Coax is 820.
Simply put, for the antenna, put a ground rod at the base of it, bond to the mast, then run a bonding conductor to the Intersystem bond. Min is 10 copper, I would use a 6 AWG. Read thru the rules in 810.21. If you can't hit the intersystem bond, then use a split bolt and go the GEC. If you don't make this bonding connection, you won't have a single point ground and run a huge risk of equipment damage from lighting

For the coax, install a listed lightning protector at the building entrance , bond it to your bonding conductor.
The antenna man has good info here https://www.antennamanpa.com/index.html

Mike Holt just sent out a newsletter with PDF on Art 810 and 820. Here is a link to his video.

I have done in the past some 50+ antennas for telemetry, it took me a while to work thru the rules but in the process I made and had accepted a code change to Art 810 (810 didn't reference art 250 for the connection of the GEC to the ground rod, meaning it could of been made with a hose clamp)
Most antenna installs are done incorrectly. The HAM radio folks are the worst.

 

[synchro]

Most antenna installs are done incorrectly. The HAM radio folks are the worst.

I would argue CB'ers instead, although there aren't too many of those around anymore especially with a base station.

 

[GoldDigger]

If you are counting on over the air digital TV, and have a long coax run it might be a good time to install a low noise preamp at the antenna.

Sent from my Pixel 4a using Tapatalk

 

[Ravenvalor]

All great info.
I will probably just bolt the antenna's 2 - horizontal support arms to the wall of the house at the gable side of the house and then run the coax cable plus a #6 sol cu bonding wire through the attic (50') to the service intersystem bonding bar. I would prefer to put it closer to the service but this is as close as I will be able to get it.
Thanks for the help.

 

[mikeames]

Can someone explain why a ground rod is needed to earth the mast assuming its bolted to a concrete base that's already earthed?

 

[hbiss]

I would say that if the concrete had rebar that was brought out so it could be bonded to the tower or mast (ufer) then yes.

But just sitting on concrete wouldn't do it.

-Hal