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Author Topic: Lightning radials  (Read 2552 times)
KB0TXC
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Posts: 80




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« on: August 17, 2013, 11:45:36 AM »

Hi again,

A quick question....

As I have posted before, I am installing my Hustler 4BTV as a ground mounted antenna. The mounting post is a driven 1-1/4 inch galvanized pipe, with thirty inches in the ground. Attached to this pipe are two bronze clamps designed for ground rods. To these clamps, I have attached ten feet of #4 bare copper wire radiating out from the pipe, and connected to 4/8 inch copper clad ground rods driven to below the ground level. The tops of the ground rod are in valve boxes, and the #4 wire is bonded to these rods. The rods are eleven feet, and reach the water table. The bare #4 wire is buried as well.

I am interested what those with more experience than I think about this and if it is sufficient.

Thank you in advance,

Joe KB0TXC
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K7KBN
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Posts: 2836




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« Reply #1 on: August 17, 2013, 12:06:11 PM »

Is this arrangement bonded to the ground rod where your electrical service enters the house?

What arrangement do you have where your feedline enters the house?
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73
Pat K7KBN
CWO4 USNR Ret.
KB0TXC
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Posts: 80




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« Reply #2 on: August 17, 2013, 12:23:52 PM »

This is just for the antenna location.

At the house, the shield of the coax will be grounded to a ground rod (as well as the central ground point). At the central ground point, there will be a Lightning arrester that the coax will go through. Everything is connected to this central ground point...the radios, the copper water inlet pipe, the house electrical ground rod, the house perimeter ground wire (and rods) that I have placed around our house, the surge protector and the telephone line lightning protector, and finally the relay control lines will go through a lightning arrester made for those things.

I am very respectful of lightning. My grandmother's house was destroyed by lightning decades before I was born. The stories that I heard as a child about this still ring through my memories as I watch thunderstorms roll through.

Best,

Joe KB0TXC
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KF6OCI
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Posts: 104




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« Reply #3 on: August 17, 2013, 02:25:27 PM »

Did your grandmother's house have electrical wiring?
Hope wiring helps.

I saw where lightning hit on a golf course and the grass was completely burned
for what looked like 100' radius around the strike. I wonder about a
strike on an antenna like 75' away. More of a personal safety concern than equipment.

Anyone have experience with an antenna strike within 100'Huh??

Dan 
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W9GB
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Posts: 2659




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« Reply #4 on: August 17, 2013, 02:31:31 PM »

Quote from: KB0TXC
I am installing my Hustler 4BTV as a ground mounted antenna.
HUSTLER BTV Antenna is a Multi-band Trapped Quarter-Wave Vertical (Marconi),
http://www.ycars.org/EFRA/Module%20C/AntVert.htm

SO by standard design the Ground Radials are 1/4-wavelength of operating frequencies.
Put down a minimum of 8, the more the better.

40 meters. A 1/4-wavelength -> 10 meters (30 to 33 feet works).  It is that easy!

Quote from: KF6OCI
Anyone have experience with an antenna strike within 100 feet.
Dan,

YES.  30 years ago, when I was graduate school -- lightning hit the roof peak of the building I was living in.  
It left a scorch mark on the ridge cap shingles (roof).
Radios and antennas, which were grounded for lightning protection, were fine (no damage).

HOWEVER, the lightning hit was above the twisted pair phone wires running in the attic
from the NW Bell drop (and lightning protectors) and my telepone outlet.
The INDUCED Voltage/Current (remember electric & magnetic theory?) from that lightning strike found their way down the phone wire to my external Hayes 1200 Smartmodem and IBM Serial Card.

The Hayes modem (dead) was replaced under warranty, the IBM XT was OK,
BUT the copper trace on the IBM Serial Card (connect to Hayes modem) was VAPORIZED.
You could see the ghost areas on the fiberglass PCB where the ground copper trace use to be.

The generous radio amateurs at Collins radio club, repaired the IBM Serial Card.
Their work was so good -- you could not tell it from original IBM card (gotta love top PCB repair talent)
« Last Edit: August 17, 2013, 02:53:49 PM by W9GB » Logged
K1CJS
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Posts: 6061




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« Reply #5 on: August 17, 2013, 02:46:38 PM »

You may want to run a separate ground cable from the antenna base to the house ground.  That may eliminate noise that you may well have on your receiver since any potential difference between the ground points will make itself evident on the co-ax shield between the antenna and the surge (lightning) arrestor you have installed at the house on the co-ax--and show up as noise on your receiver.
« Last Edit: August 17, 2013, 02:51:51 PM by K1CJS » Logged
K0ZN
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Posts: 1562




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« Reply #6 on: August 17, 2013, 09:08:25 PM »

As far as only the LIGHTNING grounding on the antenna, I would say, by ham standards (and I don't mean this to be negative), that is a excellent basic ground for the ANTENNA.

Follow up comments:  (1.) Those ground rods will do very little good as an RF ground. You need radials for that. (2.) A good, extensive RF radial system is also a significant benefit in lightning protection (assuming a decent size wire is used in the radials) as it spreads the lightning currents out. (3.) Reality is that a super effective lightning ground system can be quite costly and the cost to benefit ratio to most hams is fairly limited. (4.) Your ground mounted 4BTU is not tall enough to be a lightning attraction. It is not a "highly attractive target" based on height. There is hard data on this related to lightning protection on towers, and you are well below the height where risk of a hit begins increasing. (5.) Other posts about bonding to AC power ground, etc. are good/correct. You want to bond EVERYTHING together to prevent voltage differences.

I live in an area with severe lightning and I can tell you, if nothing else, you will sleep a LOT better knowing you made the time and effort to install a GOOD lightning ground system.

You sound like a guy who wants to do things right; protect the coax, etc. correctly too. Along that line, don't cut corners on the number of radials you put in. I put my money where my mouth is: I have a 40 M vertical sitting over a radial system of 103, thirty seven ft. radials. The antenna is a really excellent performer....actually amazing at times. A lot of *experts* will tell you you don't need that many radials, but having installed this antenna at two different QTH's, I can assure you it was the effort; I would re-install this radial system a 3rd time if need be. Most hams have no idea of how good/effective a vertical can be when it is installed over a really extensive radial system.

Good luck.  73,  K0ZN
« Last Edit: August 17, 2013, 09:21:17 PM by K0ZN » Logged
KI5FJ
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Posts: 40




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« Reply #7 on: August 18, 2013, 05:30:00 AM »

No amount of bonding/grounding will totally eliminate damage. All the previous comments are technically OK.
During my work at a 5 Kw AM station with four tower antennas, I have seen many strikes.
The feed-lines auto disconnected and all usually survived.
I have all HAM  feed-lines bonded together in the shack.The panel is connected to a ground rod.
I only connect the radios to the panel when I am operating. I don't operate when storms are in the area.
A 240 Volt circuit breaker is open when I am not operating. 73 Joe O NNNN
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KB0TXC
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Posts: 80




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« Reply #8 on: August 20, 2013, 06:35:21 AM »

Thank you all for the nice comments and thoughts. Just to let everyone know, the four radials that I have installed and bonded to the ground rods are for lightning protection only. I will be working on the RF radials this week using insulated 14 gauge wire that will be thirty seven feet long for each radial. I plan on using 120. The DX engineering ground radial plate has sixty 1/4 inch holes, so each will ultimately have two radials attached. Right now, I have the wire for about ninety radials. Will be getting the rest next month.

Thank you all again!

I will be using the many suggestions given here.

73,

Joe KB0TXC
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K0ZN
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Posts: 1562




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« Reply #9 on: August 20, 2013, 10:04:53 AM »

If you go to the effort to put in that first class radial system, you will very pleased with the performance of that antenna.  I have a similar radial system under mine
(103, thirty seven ft. radials). The performance of the antenna far exceeds what you might expect could be done with a "simple vertical".  On long haul DX the antenna
is VERY competitive if you run some power; you will see the benefits of a really low angle of radiation which a vertical with a GOOD radial system provides. I have seen cases at my QTH where the incoming signal's angle was so low that it was virtually unreadable on a horizontal antenna 40 ft. high...and S-4 (and Q-5) on the vertical. There is a lot of modeling theory that says you don't need that extensive of a radial system, but I can assure you after installing this system at two QTH's, a really large radial system seems to make the antenna perform better than it should. Once you get the system in and running, you will quickly realize the sweat and work on that radial system was a "cheap" trade off. Again, most hams just never put in a TRULY "large" radial system and never have a point of comparison. It is when conditions get marginal that you will start to see what I am talking about....and/or when you get some flattering signal reports from DX stations.   Good luck....

73,  K0ZN
« Last Edit: August 20, 2013, 10:07:53 AM by K0ZN » Logged
KI4DSC
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Posts: 65




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« Reply #10 on: August 20, 2013, 10:45:16 AM »

You are well on your way to a very nice vertical set up.  I have the 6BTV at my QTH and I work DX on less than 100 watts.  I love when I get in and then hear a station that has been calling and calling finally get in and report he has a 4 element beam up 60 feet and 1000 watts.  Just goes to show that a good vertical and play with the big boys if you do a good job installing it!

I wish I had more radials.  I am adding new radials as I can and with each bunch of 20 or so radials I notice 2 things happen.  First I see less noise from the 90 degree lob as it goes down and the lower take off angles take over.  Second I found I had to re tune my antenna.  As the antenna becomes more efficient the band width goes down, resignant frequency goes up and gain goes up.  I don't mind retuning to get more efficiency.

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KI5FJ
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Posts: 40




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« Reply #11 on: August 20, 2013, 06:31:45 PM »

Your RF return network, AKA wires running radially outward will significantly reduce ground losses.
This improvement to the bottom half of the antenna is worth the effort.
Consider installing a LINE ISOLATOR on the coax near the antenna. This common mode choke will reduce RF on the outer shield. A Poly-Phaser at the ground rod will drain off high static charges. 73 Joe O NNNN
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KB0TXC
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Posts: 80




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« Reply #12 on: August 21, 2013, 04:29:55 AM »

Hi KI5FJ,

I am waiting for the arrival of the choke UNUN mounting plate from DX Engineering. A friend of mine traded me an FM rig for the UNUN, which is itself a DX E product, but as I cannot remember what model it is, but it is for verticals... coax in one end, two standoff insulators on the other, one for the antenna and one for the ground. I am at work right now, so I cannot go look to see what UNUN model that is.

Someone suggested that I put a one to one UNUN at the shack end of the cable before it enters my house as well. Is that necessary or will it be helpful?

Thank you all again!

73,

Joe KB0TXC
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WX7G
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Posts: 6324




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« Reply #13 on: August 21, 2013, 05:55:58 AM »

With your vertical antenna an UNUN is not needed at the feedpoint or at the shack.
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KI5FJ
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Posts: 40




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« Reply #14 on: August 21, 2013, 06:39:59 AM »

Elimination of RF ground loops is a good thing. A coax feed-line near the radial field tends to act like a radial. Decoupling the outer shield is not a bad thing. I suggest you install the coax into PVC and bury it a few inches below the radials. Unless you are operating legal limit power I don't expect the RF on the outside of the coax will warrant a UNUN near the shack. To remedy stubborn RFI issues a second choke at 0.25wl from the antenna is effective. I am using a Radio-Works Line Isolator UNUN at the base of my 50 Ft Vertical. I will email a pdf of this antenna to those who are interested. Request using QRZ address. Decoupling a DIPOLE feed-line with a balun is the same issue. The balun is not absolutely necessary, BUT .. 73 Joe O NNNN
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