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Proper Antenna Grounding

Antenna grounding lightning electricity

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#1 JeremyM

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Posted 28 May 2013 - 12:16 PM

OK, being new to base station and repeater building I have a very important question. What is the best way to ground a fiberglass antenna?

 

To explain my setup: I will be installing a gable antenna mount which has a 6' extender pole on my single story home. The antenna is 3.7ft tall for an overall height of approximately 24.7ft above ground level. My location is 177ft above sea level which puts my antenna 201.7ft above sea level. I am on a hill which is at a higher elevation than a lot of the surrounding area. There are nearby trees which will extend to higher altitudes than my antenna.

 

The antenna itself is grounded with a DC ground, but I need to know how to tie this in and create a proper ground. I do not wish to damage my home or radio equipment because I ignorantly installed my ground.

 

Any and all help/recommendation is appreciated.


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#2 JeremyM

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Posted 28 May 2013 - 12:40 PM

I might add that my antenna will be on the same side of the house as my power company box, so their grounding rod is available to tie into. Would this be advisable? If so, what is the best way to connect my antenna to the grounding rod?


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#3 PastorGary

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Posted 28 May 2013 - 01:27 PM

It is against the electrical code in most jurisdictions to tie anything into the power company grounding system. Don't go there.  If a 'meter reader' walks by and sees that tie-in, it could be a bad situation financially with fines, etc.

 

One accepted method to ground your antenna system is to run a 4 gauge ground cable with lugs on both ends from a U-BOLT where the antenna attaches to the mast, and then down to the standoff gable mount bracket U-Bolt. Tape the 4 gauge cable to the mast.  Then continue with another length of 4 gauge cable from the gable mount U-Bolt down to an 8 foot ground rod that is out by at least 1 foot from your foundation.  It should also be a minimum of 10 feet away from the power company ground rod. This is necessary to distribute a lightning hit into the power company equipment away from a lightning hit at the same time into your antenna structure. Having ground rods too close together may create a high electrical pressure wave against your foundation or slab during a strike and cause cracking or an actual failure. I have witnessed this personally in Michigan.

 

There is also an OLD SCHOOL amateur radio idea that may or may not be a good idea, but I'll explain...

 

Some older hams have refused to ground their antenna systems at all. The thought behind this is that a bolt of lightning is going to seek out the best and easiest path to ground. Grounding an antenna structure makes it into a lightning rod and may actually attract lightning. Some old school hams also remove the antenna connector from the radio and place that connector inside a GLASS Mason jar so it will not contact a metal surface in the room during an electrical storm.   There have been countless discussions about this over the years, and it just may continue here now that I have mentioned it.


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#4 JeremyM

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Posted 28 May 2013 - 02:16 PM

That sounds plausible for a base station where you will only connect it when you use it, but eventually my antenna will be used for my repeater. Since I will be leaving the repeater on most of the time (and I live in Florida close to the lightning strike capital of the country) it would not be advisable to use this method. I should go ahead and ground the system properly now so I don't have to go back and do it in a few months anyway.

 

I think I will take the advice to run the 4 gauge wire to the grounding rod. Its going to be difficult to get a grounding rod that distance from the house (and the other grounding rod on this side of the house) without getting it in lawnmower territory. Would hate to forget my grounding rod is there and run over my wire with the mower. Thats something I will have to figure out.

 

Also, the ground wire needs to run directly to the grounding rod without any sharp turns correct? That could cause some issues if trying to run it underground right?


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#5 PastorGary

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Posted 28 May 2013 - 05:45 PM

Underground would be fine for a relatively short distance and you can do a large radius bend where necessary to change directions.  Before you dig, contact your equivilent to "Diggers Hotline" to have current underground utilities marked. Then, when you are finished with the digging and routing of the ground cable, take the little color coded flags that they usually stick in the ground to mark gas, water, electric, phone and cable lines, and mark the location of your ground rod with one of the flags. Spray the flag danger orange with no printing visible and it instantly becomes a warning for the lawn mower.   You CAN actually bury the ground rod completely if the flag idea won't fly, but make a detailed measurement map with landmarks as to where it is burried and place that map with your critical household papers for future reference.


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#6 JohnE

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Posted 28 May 2013 - 08:13 PM

not every one will agree w/me on this but I'll put it out there anyway.

in my 30 yrs of doing RF I have found that grounding an antenna  just makes it a better "target".

I have 6 major sites in NYC all above 400' asl none have any real antenna grounding system and I can count on one hand how many times I have had to replace an antenna from a hit.

on the other hand there is a customers site that was properly grounded and every 2-3yrs i have to go change an exploded cigar, not too fun.

now towers are a completely different animal altogether.

again this has been my experience in the north east, where you are in FL is probably a completely different matter. for a control station w/antenna 15' above the roof line I wouldn't sweat it too much.

what in the immediate area will be higher than that,light pole ,phone pole,ect..... you get where I'm goin' w/this.

some things to look at.

https://www.tessco.c...433&eventPage=1

I may have some of these around, if you want one let me know I'll send one down.

you can pick up an 8' ground rod at home depot.


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#7 JeremyM

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Posted 29 May 2013 - 02:34 AM

You guys make 2 very good points. On one hand proper grounding is a good idea, while on the other hand ground provides a path of least resistance. If I ground the antenna properly then I would surely be saving radio equipment if a strike were to happen, but at the same time I would be making my antenna a target since the lightning would have least resistance if it hit my antenna versus the tree 40ft away.

 

If the lightning were to strike the antenna when grounded it would almost surely take out the antenna while providing that path of least resistance. The antenna when grounded would also become a veritable lightning rod. If I do not ground the antenna then it would be less likely to get hit, but more likely to damage radio equipment if a strike were to occur.

 

Looks like I need to weigh the pros and cons of this situation. Do I turn my antenna into a lightning rod, safeguarding my equipment but increasing risk of strike and possibly more frequent antenna replacement? Or do I go ungrounded, thereby reducing the risk of a strike but in the event of a strike significantly increasing the chances of equipment being damaged?

 

Depending on what I decide to do I might take you up on that arrestor offer John. If I do not ground the system that arrestor would be a bit of insurance for my equipment.

 

Going back to the days of EE in college this makes sense but this is just from experiments and electrical theory from books, not real world experience. Anyone else have experience/ideas?


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#8 PastorGary

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Posted 29 May 2013 - 07:52 PM

Just an add-on....

 

If you have a GROUNDED antenna and support structure and take a direct hit, your repeater and/or radio equipment will take damage nearly 100 percent of the time.  Even with an arrestor "protecting" the center conductor of a feed line, the line itself is being subjected to millions of volts and exceptionally high relative current in microseconds.  That energy has to go someplace and even a grounded support structure and feedline arrestor will not prevent stray voltages and currents from entering the radio room. The type of device that was mentioned is OK for indirect hits, but will physically melt internally in a direct hit, spraying the room with lots of nasties.

 

I realize that this won't make your decision any easier, but weigh everything before you start construction and the very best of luck to you in whatever you decide.


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#9 Billy

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Posted 30 May 2013 - 08:50 PM

not every one will agree w/me on this but I'll put it out there anyway.

in my 30 yrs of doing RF I have found that grounding an antenna  just makes it a better "target".

I have 6 major sites in NYC all above 400' asl none have any real antenna grounding system and I can count on one hand how many times I have had to replace an antenna from a hit.

on the other hand there is a customers site that was properly grounded and every 2-3yrs i have to go change an exploded cigar, not too fun.

now towers are a completely different animal altogether.

again this has been my experience in the north east, where you are in FL is probably a completely different matter. for a control station w/antenna 15' above the roof line I wouldn't sweat it too much.

what in the immediate area will be higher than that,light pole ,phone pole,ect..... you get where I'm goin' w/this.

some things to look at.

https://www.tessco.c...433&eventPage=1

I may have some of these around, if you want one let me know I'll send one down.

you can pick up an 8' ground rod at home depot.

 

I have often thought about this myself.   I have asked many people a question and nobody has been able to answer me.  How much voltage/amperage can the average piece of coax actually carry.   Say in a lightning strike or close proximity.  Is the coax capable of transfering enough of that electrical currently to cause major damage inside the house.  I am sure it is enough to damage a radio or similar piece of electronics but I would think that the coax would actually be the week point in the transmition.   #4/6 wire is usually recommended for grounding, that little wire in the middle of the coax surely cannot transfer that much. 

 

I have seen lightning damage a few times and from what I have noticed the damage is generally restricted to the point of impact on the outside.  

 

I have my system grounded with #4 stranded (I know solid is recommended) wire into a 8' home depot ground rod.   My antenna does not require a DC ground but I do have my coax on a switch that has a center off in case a storm is real bad and I remember to put it in this position.  I sometimes feel this is overkill.



#10 PastorGary

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Posted 31 May 2013 - 06:06 AM

Most flexible and semi-flexible transmission line is only rated for a maximum internal voltage breakdowm (arc-through center to shield) averaging 5 to 7 KVDC. Lightning strikes are thousands of times more intense than that rating.  The feedline in it's entirety becomes a path to the closest ground and once the cable is compromised, the lightning strike will follow the original path to ground through the ionized air, even though parts of the coax have been vaporized.  This all happens in microseconds.

 

Having a coaxial switch with a no-connection position selected during storms is ineffective and will not prevent a strike from reaching the closest ground in a room - electrical wiring in walls, boiler or copper plumbing, etc.

 

Many persons who have been in the industry for years and years have chosen not to ground antenna structures, other than full blown commercial broadcast facilities, because of the statistical probabilities that elevating "ground" up into the sky creates a lightning rod and is ATTRACTING a strike.  If your antenna is the highest thing in the neighborhood and is GROUNDED, it's eventually going to get hit.  If your antenna is the highest thing in the neighborhood and is NOT grounded, the lightning won't "see" that structure very well because it is electrically neutral as compared to everything else around it.  But, you have to do your part in disconnecting the indoor connector from a radio in order to prevent "splash" from a close or indirect hit that produces voltages inside and outside the coax by induction.  That's why some older 'hams' disconnect the coax and place it inside a glass mason jar - to keep the end of the coax from touching or being close to anything metal that could tell the waiting lightning strike that there is a path to a ground.

 

What you may wish to do is see if your homeowner's insurance company has REQUIREMENTS regarding this topic and follow their guidelines, whether you agree with them or not. Forum participants can not tell anyone what to do regarding this overall situation - it has to be your own decision based upon all available info and statistics...............

 

 



#11 JeremyM

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Posted 31 May 2013 - 11:15 AM

I took your advice and contacted my insurance agent (mother in-law). She looked it up and spoke directly with the insurance company. If I do not tie into any electrical equipment or build a structure taller than 30' then I am fine if I go ungrounded.

 

If I ground the antenna or put it on a structure where the elevation is 30' or more above ground (requires grounding) then a licensed electrician must come out and inspect it. I already tried the argument that I have an EE degree but that doesn't mean diddly when it comes to state regulations and certifications. Plus a licensed electrician or master electrician probably knows more about the real world applications than I do or is at least more up to date.

 

I have an aluminum 1.25" OD aluminum EMT conduit as my mast. I ended up using a gable mount to get the base of the mast off the ground approximately 13.5 - 14' and extending 4' above the ridge vent. The antenna is mounted with 0.5" of the support pipe above the mast and the bottom mounting bracket is 0.25" from the bottom of the support pipe. Total height is approximately 25' which brings the tip of the antenna to about 202' above sea level.

 

This puts me under the 30' mark where I would need permits and an electrician to come out. I do not have it grounded and the LMR400 is in a mason jar (luckily I have plenty of those). Since I will be running it as a base station for a while before reconfiguration as a repeater this will do for now. I can just disconnect the LMR and put it in the jar when not in use. I will figure out something down the road closer to time for the repeater configuration.


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#12 PastorGary

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Posted 31 May 2013 - 12:21 PM

Glad that I remembered the insurance company input on things like that... nearly forgot about their requirements.

 

Sounds like y'all are in good shape, now.

 

When you get the mobile (base) that you were thinking of, let us know what kind of simplex range you are getting to an on-foot or bicycle 4 watt portable or another vehicle mounted mobile with a center loaded 5.4 db gain mobile antenna. I'd imagine about 3 miles to a portable and perhaps 9 to 11 for a mobile (25 watt with a 52 watt ERP).

 

Keep us posted and thanks.

 

 

P-G

 

=======



#13 JeremyM

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Posted 31 May 2013 - 12:28 PM

Absolutely! The mobile unit I am looking at touts a 40 watt output so I should see somewhere around 35 watt actual output plus the antenna gain. So it might be a little better. I should be ordering my mobile in 2-4 weeks, won't be too long.


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#14 PastorGary

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Posted 31 May 2013 - 12:41 PM

cool !! :D


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#15 Billy

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Posted 31 May 2013 - 07:36 PM

Most flexible and semi-flexible transmission line is only rated for a maximum internal voltage breakdowm (arc-through center to shield) averaging 5 to 7 KVDC. Lightning strikes are thousands of times more intense than that rating.  The feedline in it's entirety becomes a path to the closest ground and once the cable is compromised, the lightning strike will follow the original path to ground through the ionized air, even though parts of the coax have been vaporized.  This all happens in microseconds.

 

Having a coaxial switch with a no-connection position selected during storms is ineffective and will not prevent a strike from reaching the closest ground in a room - electrical wiring in walls, boiler or copper plumbing, etc.

 

Many persons who have been in the industry for years and years have chosen not to ground antenna structures, other than full blown commercial broadcast facilities, because of the statistical probabilities that elevating "ground" up into the sky creates a lightning rod and is ATTRACTING a strike.  If your antenna is the highest thing in the neighborhood and is GROUNDED, it's eventually going to get hit.  If your antenna is the highest thing in the neighborhood and is NOT grounded, the lightning won't "see" that structure very well because it is electrically neutral as compared to everything else around it.  But, you have to do your part in disconnecting the indoor connector from a radio in order to prevent "splash" from a close or indirect hit that produces voltages inside and outside the coax by induction.  That's why some older 'hams' disconnect the coax and place it inside a glass mason jar - to keep the end of the coax from touching or being close to anything metal that could tell the waiting lightning strike that there is a path to a ground.

 

What you may wish to do is see if your homeowner's insurance company has REQUIREMENTS regarding this topic and follow their guidelines, whether you agree with them or not. Forum participants can not tell anyone what to do regarding this overall situation - it has to be your own decision based upon all available info and statistics...............

PastorGary, thank you!   An excellent answer.   My antenna is at the 32 foot mark.  Not the highest structure in the area and just clearing my roofline. There are other non grounded satelite dishes and tv antennas in the area that are higher.



#16 JohnE

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Posted 02 June 2013 - 07:08 PM

I put up a couple of pics of my control antenna in my gallery


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#17 JeremyM

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Posted 03 June 2013 - 08:26 AM

Very nice, looks like a fiberglass omni atop a yagi? Using the yagi with a motorized mount?


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