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Author Topic: Best Practice for Grounding a Roof Mounted Vertical Antenna?  (Read 5069 times)
KD5YZQ
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Posts: 7




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« on: December 24, 2012, 10:10:44 AM »

Greetings,

Advice appreciated please...

I intend to mount a vertical antenna (10m) on my house using a gable mount and a 10 ft. steel mast, with the coax entering the house through the gable vent.  What is the best way to ground this sort of setup for lightning protection? The location is above the entry for all my utilities so I intend to run probably a #8 insulated stranded copper wire (because I have a bunch available) to a central ground where everything is tied together.  Where should I connect the top end though?  Would it be sufficient just to ground the gable mount or should I run the ground wire all the way up the mast to the antenna mount itself?
Also, I'm thinking I should also put a Polyphaser (or similar suppressor) grounded to the base of the mount, as the coax will enter the house very close to that point.  Does this sound like a good approach?  If not, what would you suggest please?

Regards,

Mike
KD5YZQ
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K1CJS
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Posts: 6034




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« Reply #1 on: December 24, 2012, 12:08:43 PM »

You're going to get so many suggestions that your head is going to spin!  There are so many different opinions to something like this that are worthless that it isn't funny.  Well, to start off....

What kind of a ground are you looking to install?  There are three basic types, lightning/static discharge grounds, electrical safety grounds, (probably not applicable to this) and RF grounds.  The basics of those systems are different, and there is practically no way to install a proper ground system unless you're prepared to spend a little money.

For a lightning/static ground, the best way to do it is to run a ground cable from the base of the mast straight down to a ground rod, then bond that ground rod to the house electrical ground rod.  Use number six cable minimum to comply with the National Electrical Code.  If you insist on running the antenna cable in thru the gable, put the polyphasor unit in the coax line at the entry point.  That isn't recommended--running the coax cable down the side of the house and putting the polyphasor unit near the ground rod is.

RF grounding is different, and probably isn't feasible for your particular installation.  The typical RF ground system involves a set of radials out from the base of the antenna, something that you would have a hard time doing in your case.
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KD5YZQ
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Posts: 7




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« Reply #2 on: December 24, 2012, 12:37:25 PM »

Right.  Just simple/basic lightning/static grounding.  I'd intended to say that in my post, but neglected to do so.

The reason for wanting to take the coax in through the gable vent is to stay out of trouble with my wife.  She likely won't appreciate too many wires running down the outside of the house.

THANKS for your reply.

Mike/KD5YZQ
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VK2WF
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Posts: 5




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« Reply #3 on: December 25, 2012, 12:31:32 PM »

He already clearly stated what type of earth hes was after.
And why can the question with - "There are so many different opinions to something like this that are worthless that it isn't funny"


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KA7NIQ
Member

Posts: 258


WWW

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« Reply #4 on: December 25, 2012, 06:26:43 PM »

Greetings,

Advice appreciated please...

I intend to mount a vertical antenna (10m) on my house using a gable mount and a 10 ft. steel mast, with the coax entering the house through the gable vent.  What is the best way to ground this sort of setup for lightning protection? The location is above the entry for all my utilities so I intend to run probably a #8 insulated stranded copper wire (because I have a bunch available) to a central ground where everything is tied together.  Where should I connect the top end though?  Would it be sufficient just to ground the gable mount or should I run the ground wire all the way up the mast to the antenna mount itself?
Also, I'm thinking I should also put a Polyphaser (or similar suppressor) grounded to the base of the mount, as the coax will enter the house very close to that point.  Does this sound like a good approach?  If not, what would you suggest please?

Regards,

Mike
KD5YZQ

WHY ground it, at all ? Is not that kind of like ASKING for a lightning strike ?
I live in Tampa, we get a lot of lightning here. Plenty of ungrounded verticals on chimney mounts down here, never heard of any ungrounded verticals ever getting hit.
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N8CMQ
Member

Posts: 362




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« Reply #5 on: December 26, 2012, 05:07:53 PM »

A simple 10 Ga. aluminum or copper (preferred) wire running down
as direct as possible to your meter box ground rod is all you need.
The wire can be bare or PVC covered in a color that provides
the best stealth on the roof or wall.
Use the pipe clamp on the ground rod for a good connection.
An antenna that is 'ungrounded', will have the majority of
current flowing into the shack, rather than to ground, where
do you want it to go?
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AE5QB
Member

Posts: 269




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« Reply #6 on: December 27, 2012, 07:17:07 PM »

OK I'm confused.  My understanding is that elevated radials should not be electrically connected to the mast because the mast then becomes part of the radial system which we don't want.  So does not connecting the radial system to a ground wire make the ground wire part of the radial system also?  My understanding is that for an elevated vertical, we don't ground the antenna at all. When the antenna is not in use, the radio can be disconnected and the antenna grounded directly, but for normal operations, there should be no ground from coax shield or radial system to earth ground.  No?
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N4CR
Member

Posts: 1666




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« Reply #7 on: December 27, 2012, 07:37:47 PM »

OK I'm confused.  My understanding is that elevated radials should not be electrically connected to the mast because the mast then becomes part of the radial system which we don't want.  So does not connecting the radial system to a ground wire make the ground wire part of the radial system also?  My understanding is that for an elevated vertical, we don't ground the antenna at all. When the antenna is not in use, the radio can be disconnected and the antenna grounded directly, but for normal operations, there should be no ground from coax shield or radial system to earth ground.  No?

Tuned radials are low impedance. The tower isn't tuned, nor is the ground wire (except by accident). The current will flow to the lowest impedance. Yes, some of it flows on the mast or the ground wire. And it radiates from there. That's what we want, right?

The point here is, if it doesn't turn into heat, it radiates. The biggest problem would be that it might not be the same polarity as your radiator. And the more tuned radials you have, the more low impedance loads are in parallel making any other path unattractive. This is the same principal as the Fan Dipole. Most of the current flows on the tuned elements. Some of it does flow on the untuned elements, but it radiates so it's reinforcing.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
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