ground rod for antenna question

[scannerjim]

Hello, I live in centeral fla so lighting is a concern . I have a diamond discone antenna mounted just above the roof line. I put a ground rod (6 foot copper) down about 1 foot away from the base of the antenna. I ran the copper wire to the antenna mast and secured it about a foot from ground level . Also the mast is not sunk in the ground (earth).
My question is have I messed with or need to do anything else as I do not understand the gound plane bussiness of antennas.
thanks for any insite I can learn ,Jim

 

[digitalanalog]

I believe you Do Not Need to ground a Discone.

Just ground the mast if it's steel.

 

[ka5lqj]

"Ground", LOL!

Hi Jim,

Let me see if I can help. Having been in "radio"" since 1958 since I was 12 years old, having read numerous magazine and book articles on the subject (before Al "Bore" invented the Internet, LOL!) gives me some insight on this.

Now, I'll ask a couple of questions and answer them.

#1. Do you have any nearby trees taller than your antenna and not within say ten feet of the house or discone or pole?

If you do, don't worry, lightning would strike the tree or taller object before it would hit the antenna or pole. If you don't however, the deeper you could "plant" the ground rod (usually nowadays made from copper-coated steel) the better off you are. Copper is a good "ground" but it's hard to drive copper into the ground as it bends, even true copper rod.

#2. What type soil do you have at the ground rod? If you have a clay or loam (good soil) then there's no worry.

If you have sand, keep it wet, but not a puddle of water. To 'enhance' the soil dig a circular trench 4 inches wide and about 12" away from the ground rod about 12" deep. Fill the trench with rock salt ice cream salt, just below the grass roots and cover with soil. Wet the trench thoroughly before putting the soil back on top. About once a week, go out and water the trench just enough to get the soil good an wet. The salt will lower the soil resistance and make it more conductive to static runoff.

Where the coax comes into the house, you need to put a good lightning arrestor, a "Blitz Bug" comes to mind and the cartridges are replaceable. The downlead coax should screw into the arrestor. There should be a "drain-off" screw connection. Use as heavy a solid piece of copper wire, uninsulated, connect it to that screw, and take it to the ground rod connection. The leftover end has to have a matching connector, usually a PL-259 UHF plug that has 50 ohm coax that will attach to the BNC on the scanner. This should solve your concern and bring you many hours of enjoyment.

Now, having said that, there are "Acts of GOD" that DO happen, LOL! You can't always depend on Mother Nature not to do the 'unexpected'. :-( However, you can further reduce your chances of getting hit, by removing the coax from the back of the scanner, open the widow, when you hear lightning and thunder, and "throw that coax *snake* out the window, to the ground and away from the house. This is when you have further prepared. Now, you might consider having an inside groundplane for 2 meters to keep up with Skywarn and bad weather. The inside groundplane may also pickup the digitally-trunked and/or "encrypted" signals of your police and fire units.

Hope this helps,
Respectfully,
73,

Don/KA5LQJ

Grid Square: EM-32

 

[scannerjim]

thanks for the info , hope your weekend was great .
jim

 

[blueangel-eric]

I believe you Do Not Need to ground a Discone.

Just ground the mast if it's steel.

all antennas should be grounded for lightning protection. how could you not need to ground a discone? i've seen this misinformation on here before. lightning don't care what kind of antenna it is.

 

[W6KRU]

all antennas should be grounded for lightning protection. how could you not need to ground a discone? i've seen this misinformation on here before. lightning don't care what kind of antenna it is.

I'm not sure I understand your statement. Where are you talking about grounding the antenna? I can think of several antennas that can't be grounded. Are you talking about the feedline gnd at the shack end?

 

[reconrider8]

im thinking opf getting a dimond discone... so what are we going to do lol

 

[blueangel-eric]

I'm not sure I understand your statement. Where are you talking about grounding the antenna? I can think of several antennas that can't be grounded. Are you talking about the feedline gnd at the shack end?

if you read the origninal post the poster installed a ground rod to ground the antenna for lightning protection. it seems half this forum don't know the difference between grounding and antenna and a groundplane. grounding the feedline would be a good idea but you must ground the mast and antenna first.

 

[W6KRU]

if you read the origninal post the poster installed a ground rod to ground the antenna for lightning protection. it seems half this forum don't know the difference between grounding and antenna and a groundplane. grounding the feedline would be a good idea but you must ground the mast and antenna first.

Ground the mast, Yes. Ground the antenna? How would you ground a yagi, or a dipole, a g5rv, etc. ?

 

[digitalanalog]

all antennas should be grounded for lightning protection. how could you not need to ground a discone? i've seen this misinformation on here before. lightning don't care what kind of antenna it is.

You DO NOT Ground the antenna....................................

 

[kb2vxa]

Why every time the issue of grounding comes up and it does all too frequently (people too lazy to read) is there so much DANGEROUS misinformation? Frankly these guys need a jolt from a bolt to either wake them up or in some cases put a bit of chlorine in the gene pool, some are so dang stupid they don't deserve to be left alive!

Can't ground the antenna? You DO NOT ground the antenna? Lightning will always strike a taller object? What are you NUTS??? My own experience says lightning HAS missed several taller objects and struck an antenna only 18' above the ground and beyond that I am speechless, utterly speechless. <sigh>

 

[blueangel-eric]

Ground the mast, Yes. Ground the antenna? How would you ground a yagi, or a dipole, a g5rv, etc. ?

Ok i'm meaning grounding the mast which essentially grounds the antenna as far as lighting is concerned. if the lightning hits the antenna it can jump to the mast and down the rod. but if the mast is nonmetallic then i have no idea how approach that.

I remember a thread just like this erupted few months ago.
http://www.radioreference.com/forums/showthread.php?t=110732&highlight=grounding

 

[petey_racer]

Let me tell you. I know other LICENSED electricians who don't even have the concept of grounding & bonding down.
It truly is scary!

 

[W6KRU]

Ok i'm meaning grounding the mast which essentially grounds the antenna as far as lighting is concerned. if the lightning hits the antenna it can jump to the mast and down the rod. but if the mast is nonmetallic then i have no idea how approach that.

I remember a thread just like this erupted few months ago.
http://www.radioreference.com/forums/showthread.php?t=110732&highlight=grounding

OK. That's what I thought you meant. Some antenna designs rely on the mast being grounded and others don't.

 

[rfradioconsult]

Of all subjects posted on RR grounding is perhaps the most mis-understood of all. To effectively provide lightening protection requires more than a ground rod driven into the earth with a piece of zip cord wrapped around it and the antenna mast. Anyone that has designed a grounding network for a commercial radio site can tell you the steps necessary to protect the equipment. The one key concept is LOW IMPEDENCE connections throughout. Motorola has a publication that addresses radio site grounding; this is a good starting point. If your scanner antenna is hit and you burn down your house rest assured your insurance company will take a close at your grounding scheme to determine if its up to code.

Most if not all VHF,UHF antennas are ground independent they do not depend on a ground connection for their operation.

Here is some basic antenna information.
http://www.electronics-tutorials.com/antennas/antenna-basics.htm

 

[jaolson101]

So if you have a solid grounding rod in place, is it suitable to use this as a grounding point for both the feedline as well as the antenna mast - or would two grounding rods be desirable?

 

[kb2vxa]

The key is SINGLE POINT GROUND in commercial and broadcast installations, that's what the NEC specifies. About the best thing you can do is run the coax to the earthing rod and insert a suitable arrestor there. You can get an extremely high, often lethal potential between separate earthing rods and even equipment that isn't properly bonded because a lightning discharge typically carries a current of about 50,000 amperes. That's a staggering amount of current and when you multiply it by a X number million volts you can say one bolt discharges in a tenth of a second what it takes a whole day for a major power plant to produce, think about it.

If you want a good idea of what sort of materials to use when grounding a mast take a look at the wire coming down a power pole and the rod driven in next to it. If you want an even better idea talk to a power company lineman, he may just have some hardware on the truck to show you.

 

[prcguy]

The single point ground recommendation is for equipment inside the building not for lightning protection. A single point ground can help eliminate ground loops and hum on equipment but for lightning protection a buried ground ring of very large diameter wire and lots of ground rods are needed.

The building I work in is about 125ft X 225ft and has 75, 8ft ground rods around the parameter welded to a 500MCM bare copper wire running around the building. There are more ground rods and ground rings around the many antennas on site antennas and I have forgotten the amount but its probably another 40 or more rods.

There are two major things needed for equipment to survive a direct lightning hit, you must dissipate the strike into the ground with very low impedance conductors and there must be a very low impedance between the lightning ground and AC ground so they both rise at the same potential during a strike.

Successful designs will dissipate as much of the strike to an antenna as possible to ground so there is very little left on the feedlines entering the building. Further bypassing of the feedlines at the building entry point with lightning arrestors, bulkhead ground plates and more ground rods can bring the potential down to a manageable level.

All of the above is nearly impossible to accomplish in a residence unless the building was designed from the ground up (pun intended) for lightning protection. In most cases an amateur or scanner operator is simply putting on a few band aids in anticipation of falling off a cliff.

Anything else in your house is at risk of damage during a direct hit including TVs, stereos, computers, telephones, etc from just being plugged into AC power or phone lines.

The point I wish to make is you should follow the NEC and best practice for lightning protection including bonding any new ground rods to the house AC ground but in the end just remember you are not fully protected and should probably disconnect antennas in a lightning storm and stay away from the feedlines. If your radio is completely unplugged and sitting in the corner it may actually survive a direct hit to your antenna, but no guarantees.
prcguy

The key is SINGLE POINT GROUND in commercial and broadcast installations, that's what the NEC specifies. About the best thing you can do is run the coax to the earthing rod and insert a suitable arrestor there. You can get an extremely high, often lethal potential between separate earthing rods and even equipment that isn't properly bonded because a lightning discharge typically carries a current of about 50,000 amperes. That's a staggering amount of current and when you multiply it by a X number million volts you can say one bolt discharges in a tenth of a second what it takes a whole day for a major power plant to produce, think about it.

If you want a good idea of what sort of materials to use when grounding a mast take a look at the wire coming down a power pole and the rod driven in next to it. If you want an even better idea talk to a power company lineman, he may just have some hardware on the truck to show you.

 

[rfradioconsult]

A oldtime broadcast engineer, long-time ham and a well-known former CQ writer; told me once that in the broadcast industry at their transmitter sites it used to be SOP to take the ac line cord for their equipment and tie a knot in it. This would help to protect the equipment from lightning induced surges.

 

[ka5lqj]

Isn't that what I said? LOL!

The single point ground recommendation is for equipment inside the building not for lightning protection. A single point ground can help eliminate ground loops and hum on equipment but for lightning protection a buried ground ring of very large diameter wire and lots of ground rods are needed.

The building I work in is about 125ft X 225ft and has 75, 8ft ground rods around the parameter welded to a 500MCM bare copper wire running around the building. There are more ground rods and ground rings around the many antennas on site antennas and I have forgotten the amount but its probably another 40 or more rods.

There are two major things needed for equipment to survive a direct lightning hit, you must dissipate the strike into the ground with very low impedance conductors and there must be a very low impedance between the lightning ground and AC ground so they both rise at the same potential during a strike.

Successful designs will dissipate as much of the strike to an antenna as possible to ground so there is very little left on the feedlines entering the building. Further bypassing of the feedlines at the building entry point with lightning arrestors, bulkhead ground plates and more ground rods can bring the potential down to a manageable level.

All of the above is nearly impossible to accomplish in a residence unless the building was designed from the ground up (pun intended) for lightning protection. In most cases an amateur or scanner operator is simply putting on a few band aids in anticipation of falling off a cliff.

Anything else in your house is at risk of damage during a direct hit including TVs, stereos, computers, telephones, etc from just being plugged into AC power or phone lines.

The point I wish to make is you should follow the NEC and best practice for lightning protection including bonding any new ground rods to the house AC ground but in the end just remember you are not fully protected and should probably disconnect antennas in a lightning storm and stay away from the feedlines. If your radio is completely unplugged and sitting in the corner it may actually survive a direct hit to your antenna, but no guarantees.
prcguy

I was also pointing out how to lower the take-off angle of a common groundplane and by adding radials a half wave-length down could improve reception and transmission of signals (Skywave vs Groundwave). Also I did mention removing the coax from the scanner and throwing the coax out of the window on the "ground" (Earth), so that just in-case lightning were to strike it would go to "ground" from out of the coax.

ALL of my equipment is connected to a 1" copper ground buss and to an 8' ground rod with # 4 copper wire, as short as possible in back of the operating position, ham gear, scanners, computer cases and all, LOL!

Respectfully,
73,
Don/KA5LQJ