eHam.net - Amateur Radio (Ham Radio) Community

Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net



[Articles Home]  [Add Article]  

Alternative Antenna Grounding Techniques

(NO6L) on January 22, 2011
View comments about this article!

Some Alternative Antenna Grounding Techniques


Copyright © 2011 Chuck Ruff, NO6L

Scope

Applying a DC ground to an antenna system, as most radio amateurs know, has two benefits; one, is for safety due to lightning strikes. The second is quieter reception as unwanted static energy is bled to ground. The two most popular HF antennas are also the most vulnerable to both phenomena; one, the dipole is susceptible because only one side can be grounded reliably. The other one is the Marconi or vertical because it is most like a lightning rod. As such, I will concentrate my attention to these basic antenna designs. There have been attempts to remedy the DC ground situation. Some can only dispense with static discharge and have no effect on dissipating a lightning strike, and may at best have no affect.

The first thing usually tried is attaching a high value resistor across the antenna terminals. This does a great job of dissipating static charge and it’s cheap. Usually a 200,000 Ohm or 300,000 Ohm 2-watt resistor is enough. And it won’t do a thing for protection against lightning.

An inductor is the next thing that can be applied. It has a greater current carrying ability than the resistor. A vertical with an extensive ground system has a feed impedance of about 36 Ohms, so a shunt inductor across the terminals can increase impedance to 50 Ohms and also provide a DC ground and protect the station from a lightning strike. Or can it? We’ll return to this in a moment. A dipole is another story. Its feed impedance is higher than 50 Ohms, so a shunt inductor to provide a DC ground and affect a more desirable match is not an option. A choke type inductor is the only option here. Both remedies have a common issue when it comes to lightning strikes. The choke or shunt inductor can induce high voltages itself across the feed line during the strike when the magnetic field contained within it collapses, and can actually feed energy directly into your equipment anyway, not at all desirable. Also, a choke would only be good to quiet a noisy antenna and would be no more protection than a resistor, and it costs more.

A shorted band pass stub is another possibility and will work much better. However, it is a single band/frequency device and is limited by the current carrying abilities of the center conductor in the stub. Also, at 80M and 160M it becomes very long. This option is not viable when you are using a multi-band vertical or fan dipole/inverted “V”, as I am, to conserve real estate.

In the rest of the paper I will present a fourth alternative that will remedy the situation using the W2DU Balun on verticals and what I’ll term an NO6L Balun on dipoles. And because there is no solenoid type of inductor, it has no coils of wire to induce a voltage during a lightning strike, and maybe make the situation worse.

The Test and Control Setup


Figure 1

Here I present the test setup and the baseline control experiment that I will refer to during the presentation of the actual subject of this paper. In Figure 1 is a photo of the test setup. Carbon composition type resistors were used in order to remove any doubt whatsoever of the possible inclusion of reactance into the test setup, short of what is produced in the short lengths of exposed coax, leads of the resistors, etc. The groups of ½ watt resistors were hand chosen to produce exact values of 50 Ohms and 25 Ohms. The groups are of 100? resistors. The feed line is RG-174, miniature 50? coax. The extra wire attached to the ground plane in the upper left is going to be used in what I term a “Balun Return” circuit. A large sheet of aluminum is used as a ground plane to reduce inductive reactance.


Figure 2

In Figure 2, I establish a baseline control. The fact that it is not a perfect match is not of importance. What is important is that the measurements, as we proceed, do not change significantly from the baseline set forth in this control experiment.


Figure 3

In Figure 3 and 4 I establish the viability of the W2DU Balun as a way to decouple a coaxial feed line from a balanced antenna. In this case it was made using 65 ferrite beads. I did not determine the permeability of them because there is more than enough for these experiments at 14 Mhz. An actual W2DU Balun would consist of 12 or more inches of Amidon #73 material, beads for example, for 1.8 – 30 Mhz. The dipole without a balun is simulated with a “split load” consisting of two 25 Ohm resistors in series with the center tap grounded. As can be seen in Figure 3 there is a significant amount of inductive reactance influencing the match of the load to the feed line.


Figure 4

Figure 4 shows the W2DU Balun installed and functional as is indicated by a significant drop in inductive reactance towards what was encountered in the baseline control experiments. The resistive component returns very close to normal as well. This is what is in line with what is established in Walter Maxwell’s conclusions presented in his publication, Reflections II ©, pages 21-6 to 21-10 using the same experiment. This concludes the control experiments and I will now proceed with the actual subject of this paper.

DC Grounding a Vertical Antenna

In Figure 5 I am simulating a vertical antenna, the shield is grounded and the center conductor attached to the actual antenna, in this case the “hot” side of the resistor. As can be seen, the readout on the analyzer is showing normal and in line with what is established in the control experiments.


Figure 5

Now, let’s look at Figure 6 with the W2DU Balun installed. Notice the shield and center conductor are reversed! Not only that, the Balun Return is also attached to the center conductor producing a complete DC short from center to shield. And on the analyzer readout there is virtually no change in the resistive and inductive components. If this were a vertical antenna and the shield of the feed line were grounded at both the base of the antenna and the entrance to the shack it would be safer by magnitudes during a lightning strike.


Figure 6

Again, some may think this is superfluous if you use a shunt inductor to match a 36 Ohm Marconi/Inverted L Antenna to a 50 Ohm feed, but remember, as was mentioned above concerning using an inductor to provide a DC ground, it can produce a spike across the feed line during a lightning strike. To limit this, simply install the W2DU Balun and Balun Return circuit before the shunt inductor and antenna terminals.

DC Grounding a Dipole

In Figure 7 we see a simulated dipole. The W2DU Balun is installed and one side, center conductor, is not at a DC ground. A lightning strike on this wire will be sure to have an impact in the health of your station equipment. You basically have a 50% chance of a direct strike here. However, even a direct strike on the shield side pretty much guarantees an impact on the center conductor side, either through arcing/shorting the feed line, or by inducing currents there. Either way, the prospects of your rig surviving this punishment, if you accidentally leave your feed attached, is nil at best.


Figure 7

In figure 8 we see the cure using the NO6L Balun. It is the same thing as a W2DU Balun with a twist. I have attached the Balun Return, with the same number of beads, 65, around it as the W2DU Balun from shield before the balun to the center conductor on the antenna side. Best of all, as the analyzer shows, there is again virtually no effect, positive or negative, regarding matching of feed line to antenna. Only a complete and certain DC ground. An apparent alternative is to “hairpin” the Balun Return across the terminals of the antenna, but this does not route to ground as directly as to the station side of the balun and as a result doubles the amount of inductance, possibly allowing more of the EMP pulse to enter the feed line through the center conductor. It’s also mechanically un-wieldy.


Figure 8

Other Applications and Notes

The prospective DIYer could use “binocular” ferrites, of 73 material of course, and run the feed line up one side and the Balun Return up the other. Then you would not have double the parts in the balun, will be easier to fit into a tubular enclosure and it may be cheaper than twice as many ferrite beads.

There are other applications that the “Balun Return” type of device can be used on without the W2DU portion. It can be applied across a loop, sky wire or cubical quad, to short out any pulses that may be induced in the antenna during a strike. On a quad, bond the shield further down the boom or other structure with a “bulkhead connector” for a completely DC grounded cubical quad antenna.

Is a Gamma Matched antenna really DC grounded? No, there is an open path between the center conductor and the Gamma Capacitor. Simply run the wire with the beads on it between the center of the SO-239 and any convenient ground. Then the whole antenna is grounded, not just 99% of it.

Even long wires and beverage antennas can be better DC grounded. Install the W2DU Balun just like I presented for the vertical using a Balun Return wire before the matching circuits.

If you already have a W2DU Balun installed on a dipole or inverted “V”, simply route an external Balun Return with beads on it from the center conductor side of the balun back to the shell of the PL-259. Use a small hose clamp to attach it to the outside of the PL-259 instead of cutting open the coax jacket to gain access to the shield or soldering directly to the PL-259.

Use a heavy wire for the Balun Return, 10 AWG should be sufficient. This is the last place you need a “fuse”. For maximum protection, ground the shield before the W2DU or NO6L Baluns at the base of the vertical antenna or the closest point that you can for a dipole. This will allow the shield to shunt as much of the strike energy as possible to ground before entering the shack.

Disclaimers and Acknowledgements

I and any publisher or other distributor of this article cannot and will not be held responsible for either the proper or improper implementations of devices or suggestions contained in this paper resulting in damage to property or person. The reader assumes all responsibility in use of the information contained herein. Sorry, but as radio amateurs we deal with lethal energies, man made and natural and too many people are out to sue to “Get rich quick”. I just wish I didn’t have to waste my time putting things like this in here.

There is no substitute for completely disconnecting your feed lines from not only equipment, but also from your shack if you’re going to be away for a while or if lightning strikes are a certainty.

I would like to acknowledge that I could have gone further by demonstrating current/voltage distribution in the resistive antenna simulator networks to further bolster my conclusions. But I figured that using VSWR, resistive and reactance results to extrapolate the behavior of them would be more than adequate to effectively present my theories. It would have also made the paper much longer.

I would like to take a moment to thank Walter Maxwell, W2DU, for his work in the “Antenna Arts”, publications and the W2DU Balun design.

I would also like to thank the people that manufacture the Rig Expert AA-230 analyzer (www.rigexpert.net) for a fine and very affordable antenna analyzer. Keep up the good work, guys!

If you would like a reprint of this article in MS Word .doc or Adobe .pdf formats email me at chuckathie(at)gmx.com .

“Some Alternative Antenna Grounding Techniques” and “NO6L Balun” are copyrighted ©, 2011. No portion other than pull quotes may be distributed for financial gain without the authors written permission. And the author will most likely give permission, just ask.

Chuck Ruff
NO6L

Member Comments:
This article has expired. No more comments may be added.
 
Alternative Antenna Grounding Techniques  
by KC8ZEV on January 22, 2011 Mail this to a friend!
Outstanding article! Useful and practical, will give it a try to quiet my dipole.


73

KC8ZEV
 
Alternative Antenna Grounding Techniques  
by WS4E on January 22, 2011 Mail this to a friend!
Great job on the photos and the getting good lighting on that LCD screen which can be very tricky.
 
RE: Alternative Antenna Grounding Techniques  
by K3AN on January 22, 2011 Mail this to a friend!
Wow! And here I thought that, in order to protect against a lightning strike, I needed a solid ground connection (at ground level) to the coax shield, a Polyphaser-type device to protect the center conductor, one or more station/antenna ground rods, heavy wire to bond these ground rods together, and another run of heavy wire to connect my station ground rods to the electrical service ground rod.

A balun is a lot simpler and cheaper!
 
Alternative Antenna Grounding Techniques  
by KB1GMX on January 22, 2011 Mail this to a friend!
All my reading and practice on lightening grounding stations and antennas have had one thing that is a no-no.

Any inductance or reactance in the lightining ground path is means it will try to find an alternate path usually by arcing across the impedance destructively.

While the antenna will be quieter, for lightining there still has to be an alternate path. Static electricity is easily dealt with by providing DC
paths to dissipate it. Keep in mind static noise is not from the charge itself but it's buildup that
eventually leads to discharges (micro lightening). Lightening due to it's high impulse energy and bandwidth cannot be handled that way.

Lightining is an AC RF impulse and requires respect for total energy and bandwidth.

There is an excellent opportunity for observation there with the vertical case that if the isolating balun is doing it's job the resulting connection at the load end is being fed balanced (leads are interchangeable). Unfortunately the load is still unbalanced (vertical).

I also suspect at 14mhz that ground plane provided is largely meaningless due to small size relative to wavelength. Add to that relatively sort coax and your do not see all the dynamic interactions of a real full size 20M antenna and 50-100Ft of coax feeding it.

Allison
 
Alternative Antenna Grounding Techniques  
by KB1GMX on January 22, 2011 Mail this to a friend!
"Is a Gamma Matched antenna really DC grounded? No, there is an open path between the center conductor and the Gamma Capacitor. Simply run the wire with the beads on it between the center of the SO-239 and any convenient ground. Then the whole antenna is grounded, not just 99% of it."

I'll address this separately as this is not a matching
question but basic lightening protection case.

Yes and maybe.. Yes, for static as the element halves
are one piece and the coax shield connects to the center point. For lightening protection the element must be bonded to the boom, mast, tower and then ground with minimal impedances at every junction. The exact reason for maybe answer is that the coax shield is sufficiently DC resistive (ohms law, 0.1 ohm and 10,000A=100,000V!)to allow an excessive voltage build up along its length leading to arc overs and other nasty effects. Under those conditions (direct hit) you can see the specific DC termination of the center conductor is largely meaningless (should have protection though).

NOTE: the actual voltages for a hit can vary hugely but
the key is that the current will be thousands of amps
and the DC resistance as well as AC resistance of the path to lightening ground must be minimal with none
of the user gear in the path to ground. The latter is why everything in the air goes to physical ground, then to the station.

Anyone thats been to a repeater site, cell site, or broadcast station has seen the extensive ground system
and how specifically it's applied. Oddly these sites take hits and keep working and are designed so to be uninterrupted.



Allison

 
Alternative Antenna Grounding Techniques  
by K0IC on January 22, 2011 Mail this to a friend!
As someone who likes to keep things simple, I am following the sage advice of WA9ENA by grounding to earth ground one side of the 4:1 remote balun outside the house. I tune the 170-foot dog-leg long, ten-foot high, lazy end-fed antenna with my MFJ tuner, currently a 941D. It works great, especially after I re-soldered and re-tightened screws/bolts in the tuner. I need to tighten the nut on the tap selector and lock it with either Loctite or fingernail polish to keep it from wandering and loosening. After doing so the antenna is "easy copy," into Florida and similar distances on 20 meters.
 
RE: Alternative Antenna Grounding Techniques  
by N3JBH on January 22, 2011 Mail this to a friend!
I was surprised by your ratings for wattage of the resistors. I was under the impression that if you was running a large amplifier you needed much heavier wattage ratings. Of course i am not a engineer and quite honestly leave a lot to speculation and belief to what i read but i been using 50 watt resistors on my antennas. maybe it has been over kill !!! How ever it sure has worked as you stated. Jeff
 
Alternative Antenna Grounding Techniques  
by KB1GEJ on January 22, 2011 Mail this to a friend!
Great information! My strategy has been rather simplistic: I keep my coax outside until I need it. the connector is under a plastic bucket with a brick on top. Works for me, although it makes it hard to hook up pre-dawn in winter to catch those grey-liners.
 
Keeping it simple.  
by AI2IA on January 22, 2011 Mail this to a friend!
When lightning threatens you go outside. You disconnect your transmission line from its input to your shack, and you ground your transmission line from the antenna. You can also ground the whole antenna.

It takes just a few minutes. It has years of experience behind it. It is simple, cheap, and reliable.

The more you add, the more things you have to go wrong.
 
RE: Alternative Antenna Grounding Techniques  
by NO6L on January 23, 2011 Mail this to a friend!
by K3AN on January 22, 2011
"...Wow! And here I thought that, in order to protect against a lightning strike, I needed a solid ground connection (at ground level) to the coax shield, a Polyphaser-type device to protect the center conductor..."

Where in the presentation did I say or imply that one could dispense with any other lightning protective devices? Could you please point it out, without sarcasm, if possible.
 
RE: Alternative Antenna Grounding Techniques  
by NO6L on January 23, 2011 Mail this to a friend!
KB1GMX,

I am aware of the different types of noise that can be absorbed by an antenna and when I said that grounding a dipole or Marconi antenna with my technique would help decrease noise that people would know what I meant. To further explain would have made the already long article too ponderous.

As for applying a choke balun to a Marconi or ground plane antenna, I'd like to direct your attention to the article "Ground-Plane Antennas", page 6-18 of the ARRL Antenna Book, 21st Edition. All I did was invert the choke balun and ground the lead attached to the center conductor. You may be confusing feeding such an antenna with open line feeder, which is not practical, but not impossible.

If there is some kind of "dynamic reactions" concerning feed lines and antennas beyond what is intended with stubs or feed line transformers then there is a problem somewhere. As per Maxwell and other authors feed line length, other than losses are irrelevant.

The "ground plane" used in my experiments are in no way related to a ground plane used as a counterpoise in a Ground Plane antenna system. It is like the ground plane used on the underside of a circuit board for a solid state RF power amplifier or VHF or UHF striplines. To provide a low reactance path back to a common ground, nothing else.

In your second post, matching is not the purpose of my two uses of a choke type balun.

As for DC grounding the coax side of a gamma match, I would much rather use a "T" match or hairpin match which are DC grounded by their nature. However, using a length of heavy wire with #73 material on it to ground the center conductor just, as I said, adds a little more safety. Use it or not, it's your call.

I once again never said this is a substitute for proper lightning protection techniques. Why it's been brought up several times at this point escapes me.
 
RE: Alternative Antenna Grounding Techniques  
by NO6L on January 23, 2011 Mail this to a friend!
KB1GEJ

"...My strategy has been rather simplistic: I keep my coax outside until I need it. the connector is under a plastic bucket with a brick on top. Works for me..."

Works for me, too! There are great lightning/EMP protection devices available, but nothing beats completely removing the threat.

However, by putting a Balun Return on a dipole for example, you may be able to lessen the chances of having to replace a feed line that got severely arced during a strike, seeing as how coax is not getting cheaper.

73
 
Alternative Antenna Grounding Techniques  
by NO6L on January 23, 2011 Mail this to a friend!
I checked the price of #73 binocular type ferrites, forget it, stay with toroids or beads, unless you're wealthy. But they are available.

Sorry, I should have checked before finalizing the article.

73 all...
NO6L
 
RE: Alternative Antenna Grounding Techniques  
by W8JI on January 23, 2011 Mail this to a friend!

I don't think the shunt impedance is a bad idea in antennas subject to change buildup, I just think there are better options (like an RF choke or higher Q ferrite with multiple turns through each core).

Lightning contains considerable high frequency energy. There is a great deal of energy at very low frequencies, but more than enough to cause a problem with damage from higher frequencies.

The problem with dc grounding systems is to pass RF, they must also by definition pass much of the energy in lighting.

Each ferrite bead of the type used in the W2DU balun looks like a low value resistor at HF and each bead is capable of dissipating about 1/2 watt. A string of beads like W2DU suggests is good for 50 ohm systems with modest to low common mode current, but is NOT good across the feedline from conductor to conductor at high power. 73 material is about 50-100 ohms per linear inch of material at lower HF. If you have 10 inches, you in effect have a ~1000 ohm resistor.

If we shunt a transmission line with a 1000 ohm resistor, we have E^2 / R for heat. We have 274 volts RMS at 1500 watts into 50 ohms. This is 75 watts of heat in the beads for ten inches of beads. It takes a very long string to not overheat the beads at high power on lower bands.

Walt used the beads for suppression, and wanted a modest resistance. He also used the beads ONLY over the shield where they only suppressed common mode currents, not across the coax.

I do think anyone depending on or considering any "dc grounding" of an element as a significant improvement in direct or nearby strike protection is mostly kidding themselves. For a static drain in an antenna prone to charging the feedline, I'd just buy a cheap 1 mH RF choke or wind something high Q.

73 Tom

 
RE: Alternative Antenna Grounding Techniques  
by K3AN on January 23, 2011 Mail this to a friend!
DC grounding is just that- DC grounding. Lightning is a pulse with a very rapid rise time, and lots of energy in the HF range, where baluns have a high impedance. The balun cores may survive the first few nanoseconds of the stroke, but they will likely be vaporized shortly thereafter as they try to resist the flow of many kilowatts of HF energy.

Lightning damage can only be reduced/eliminated by providing a VERY low impedance path, from DC well up through the HF range, to dissipate the stroke into the ground. Needless to say, the balun can NOT have a low impedance in the HF range.

A balun-type device can eliminate static buildup, but so can a high-value carbon composition resistor.
 
RE: Alternative Antenna Grounding Techniques  
by AA4PB on January 23, 2011 Mail this to a friend!
"I was under the impression that if you was running a large amplifier you needed much heavier wattage ratings"

1500W will create 274 volts across a 50 Ohm antenna load. If you parallel the load with a 1/2 watt resistor, the resistor value will need to be at least 151K. You can actually use a much higher value resistor than that to discharge static build up on an antenna. You must use a non-inductive resistor like carbon or the reactance will be be frequency dependent.

Providing a DC ground will discharge static build up like precipitation static or wind static but it won't do anything for atmospheric noise like distant lightning crashes or other band noises.

For a typical ham installation MOST lightning damage is NOT caused by a direct hit to the antenna. It is caused by inductive coupling into the antenna and feed line from a nearby strike to something else. To minimize damage from that you need a single point ground at the shack entrance.

A balun or ferrite beads won't do much for a direct strike, or probably even a nearby strike, because the high voltage will just arc across the balun windings. Again, the solution is a single point ground at the shack entrance to keep current from flowing into the shack and through the equipment.

Disconnecting the equipment only works if you put the coax outside, away from the house, and you can guarantee that it will ALWAYS be outside when lightning occurs. Forget once and your equipment can be toast.

 
Alternative Antenna Grounding Techniques  
by DK8IF on January 23, 2011 Mail this to a friend!
Dear Chuck,
Thank you very much for your grounding report, very in formative and it is a big help. I have two dipoles for for 80 and 40 together in one Balun BN86. Do you suggest also a grounding with resistors herre, and if so, where and which resistors? I would appreciate very much your news, thanks a lot in advance,
Vy 73 de Franz DK8IF
 
Alternative Antenna Grounding Techniques  
by OK1RR on January 23, 2011 Mail this to a friend!
Although nicely compiled, it is not more than a set of notoriously known facts. In other words, copyrighted Ohm's law (or if you want, Kirchhoff's law). Nice photos added, indeed, no doubt this article can help many others, but why "copyright"? Would we need to add a license type to every helpful word which can be found in 80 year old textbook?
 
Alternative Antenna Grounding Techniques  
by NO6L on January 23, 2011 Mail this to a friend!
Again, the resistors are NOT part of the circuit, they are only to simulate a resonant antenna. I made this point very clear in the article.

And yet again, this is not a substitute for proper lightning and EMP protection, it only adds more protection than a solenoid, multiturn toroid inductor or resistor can.

I know what type of energies are contained in a lightning strike or EMP pulse and others can also search/look up these things. If you feel that there is a need for this information close at hand here, please compile an article and submit it or point out one already submitted so I and others can read it and be more informed.

I'm not copywriting Ohms or Kirkoffs Laws any more than Walter Maxwell, for example, did in his publications. If you have questions concerning copywrite issues please investigate them yourself instead of telling me I'm wrong for executing one.
 
RE: Alternative Antenna Grounding Techniques  
by N3JBH on January 23, 2011 Mail this to a friend!
"The first thing usually tried is attaching a high value resistor across the antenna terminals. This does a great job of dissipating static charge and it’s cheap. Usually a 200,000 Ohm or 300,000 Ohm 2-watt resistor is enough."

Sounded to me like you was implying it was part of the circuit. I am confused now. I agree it wont stop a direct strike. i doubt few things will. Notice i said few things !!! But i pretty well done what you described in the above quotation. only differences i used closer to 1 megaohm resistors and 50 watters on my set ups. and under certain weather conditions it has made quite a difference. I freely admit i never gave W8JI's idea of 1 MH chokes a try all though i am open to tying this in the warmer future. Jeff
 
RE: Alternative Antenna Grounding Techniques  
by N3JBH on January 23, 2011 Mail this to a friend!
http://www.ad5x.com/images/Articles/Static%20Bleed.pdf
 
RE: Alternative Antenna Grounding Techniques  
by NO6L on January 23, 2011 Mail this to a friend!
N3JBH

I thought you meant the 25 and 50 ohm resistors used in the simulations.

The high value 2 watt resistor is another thing. That would just go across the antenna terminals. The reason 2 watts is suggested over smaller wattage ones is they also have a much higher voltage rating. Carbon composition 2 watts resistors are about 750 volts. Metal film types are a bit higher yet and the resistive element is cut in a helix, like a wire wound resistor and should not pose a problem unless it were self resonant on a frequency used by the antenna. Maybe someone has an idea what the issues of this would be.

73
 
RE: Alternative Antenna Grounding Techniques  
by NO6L on January 23, 2011 Mail this to a friend!
N3JBH

Thank you for that, I'll read through it. Could come in handy when I set up at our permanent QTH soon.
 
RE: Alternative Antenna Grounding Techniques  
by NO6L on January 23, 2011 Mail this to a friend!
W8JI

Your conclusions do make sense. That would also explain the infrequently reported overheating of W2DU baluns. Under the right conditions, the length of the shield on the outside of the coaxial feed line taking into consideration velocity factor could present a very low impedance load on the station side of the balun. One idea could be to use a higher permeability bead/toroid on the Balun Return and make two passes quadrupling inductance.

My using the plain "inverted" W2DU balun at the base of a Marconi I think still has merit as is because it is grounded without additional ferrite/powdered iron elements.

Thoughts?

73
NO6L
 
RE: Alternative Antenna Grounding Techniques  
by K6AER on January 23, 2011 Mail this to a friend!
Several components in lightning make it as a hard form of energy to dissipate to a safe level. The RF component is millions of watts of RF energy from the DC to well over 500 MHz. A typical lighting strike is about 8 uS or about 125 KHz. Even with the largest amount of energy in the KHz region we can hear a lightning discharge on any HF/VHF frequency for thousands of miles. The 8 uS strike frequency is well below the properties of type 43 or 61 material used in choke baluns.

The problem with RF beads on the coax is although they will reduce the common mode RF currents on the shield the high energy voltage of a lightning strike which has ionized a path for several miles of air will see the RF beads as a bit of conductive resistance. Also even when a dipole is fed with RG-8 the coax is most likely to arc over to the ground shield at the antenna, connector or a weak spot in between. Now you have many thousands of watts looking for an earth ground.

It is far better to mitigate the voltage at the lowest impedance potential which is at the earth ground bonding point. This is generally at the tower base. A strike onto the shield or tower can through capacitance or magnetic coupling place thousands of volts of energy into the center conductor. All the beads in the world will not stop the coupling physics.

Where most hams run into problems is not in buying lighting protections devices but in the application of grounding and placing a low impedance coupling to the earth ground. The thought that a single 8 foot ground is enough in many cases is no more than a poor ground.

All your ground potentials have to be bonded and don’t forget the AC panel. Ninety percent of lighting energy comes from the AC feed looking for a good earth ground. A power pole top wire hit can travel for miles. Almost all AC panels have no surge protectors attached. Hams worry about antennas being struck and leave the(AC feed) back door open.
 
Alternative Antenna Grounding Techniques  
by NC4TB on January 24, 2011 Mail this to a friend!
Great article, but I am puzzled by the effect of grounding the antenna to prevent a lighting strike. Doesn't this make it more likely that it will be struck,as lighting seeks the path of least resistance? I formerly grounded my dipole when not in use but now simply disconnect the ladder line outside my home and ground the rest of it where the line comes through the concrete block wall. And disconnect all connections to the radio including the power plug and ground. Also, the ladder line is connected to a couple of spark plug type arrestors between the outside disconnect and the dipole. Thus far no problems,despite several strikes to trees within 75 yards of the dipole. I do not operate if thunder is heard.
I can see that the high resistance shunt between the feed would be useful to reduce static build-up on the antenna and reduce the noise level.
 
Alternative Antenna Grounding Techniques  
by KB9CRY on January 24, 2011 Mail this to a friend!
A properly designed and installed lightning grounding system does an excellent job of dissipating static. Since everyone should have that then anything else is just extra.

Also disconnection is not an effective means of protection unless one has everything disconnected from all equipment and never connects it. We should be worried about induced energy surges from nearby strikes more than a direct strike.

And to those who think this will attract lightning need to di more homework on how lightning works and his strikes form.
 
Alternative Antenna Grounding Techniques  
by KB9CRY on January 24, 2011 Mail this to a friend!
A properly designed and installed lightning grounding system does an excellent job of dissipating static. Since everyone should have that then anything else is just extra.

Also disconnection is not an effective means of protection unless one has everything disconnected from all equipment and never connects it. We should be worried about induced energy surges from nearby strikes more than a direct strike.

And to those who think this will attract lightning need to di more homework on how lightning works and his strikes form.
 
RE: Alternative Antenna Grounding Techniques  
by NC4TB on January 25, 2011 Mail this to a friend!
Then why are lighting rods used, if they don't attract lighting that would have ordinarily have struck nearby, causing damage to unprotected structures/equipment? I realize that the idea of grounding the antenna is to keep a strike out of a shack but isn't the principle the same? Grounded is grounded. If a lighting rod was desired,thats what I would put up. And yes, I do disconnect everything when not in use and do not operate during thunderstorms, nearby or otherwise. All equipment is electrically isolated,even from ground, to prevent backsplash from a nearby hit.
 
RE: Alternative Antenna Grounding Techniques  
by AA4PB on January 25, 2011 Mail this to a friend!
Leaving your antenna ungrounded does not guarantee that it will not be hit by lightning. If it is hit and it is ungrounded then the likely hood of damage is high. If its properly grounded then the likelihood of damage is minimized. So the smart thing is to have it properly grounded.

Again, **MOST** of the damage to the typical amateur installation comes from currents induced into the antenna and feed line rather than a direct strike to the antenna.

If you've got a 100-foot tower on the top of a hill then it makes a pretty good lightning rod whether or not you have it grounded so best to properly ground it. I'm not considering that to be a "typical" amateur installation.

Lightning rods are intended to take the "hit" and provide a low impedance path to ground in lieu of having it punch a hole in your roof and start a fire.

 
RE: Alternative Antenna Grounding Techniques  
by KB9CRY on January 25, 2011 Mail this to a friend!
Bingo... Lightning rods do not attract lightning, they only provide a direct and low impedance path to ground.

Upon doing more lightning homework you will learn that a system that dissipates static will also help reduce the likelihood of the ground leader from forming....yes there is a simultaneous lightning bolt that forms from the ground up and meets up with the sky bolt.
It is heavy stuff to comprehend.

And double bingo in that induced charges and voltage potentials are the killer of equipment.....bone up on Induction.
 
Alternative Antenna Grounding Techniques  
by KB9CRY on January 25, 2011 Mail this to a friend!
Oh.... I never disconnect....too much to mess with.
 
Alternative Antenna Grounding Techniques  
by KB9CRY on January 25, 2011 Mail this to a friend!
Oh.... I never disconnect....too much to mess with.
 
RE: Alternative Antenna Grounding Techniques  
by WA2JJH on January 25, 2011 Mail this to a friend!
I too just disconnect. If you want to have some fun during the down time is an old trick.

Hook an NE-2 Neon bulb to the feed line.
You will see the 80V+ bulb fire faintly. As the lightening gets closeer, the bulb may be glowing bright most of the time.

Should the bulb flash like a XENON strobe, you can be sure there was a lighting strike too close for comfort. The bulb has a burnt yellow tint. The Neon ionised. You may find the bulb will not fire, unless you get another close one. You can get the bulb to flash another time. Your neon bulb is now dead.
Just think what could have rig. Some dude purchased an entire spare TS-850 front end board from me.
The photos he sent of the board were amazing. The lightening really did a number on the board.

 
RE: Alternative Antenna Grounding Techniques  
by K6AER on January 25, 2011 Mail this to a friend!
Every day there are millions of broadcast, public safety, aircraft, military and cell sites that never disconnect their feed lines when lightning strikes. These sites rarely go down due to a lightning strike.

While I was at Sprint we had over 190,000 cell sites. In 2007 we had less than 30 sites go down due to surge issues. Most of these were failure of overhead DSL lines. Proper surge protection techniques and grounding work very well. But there is no short cut. It has to be done right.

Where hams run into a problem is they don’t apply proper grounding principles to the whole station. As a result, high energy surges will compromise the station. One ground rod applied improperly can do more damage than nothing at all.

Folks worry about towers attracting lightning but the tower height is a very small fraction of the total distance lightning travels. The earth impedance has more to do with leaders traveling up to form a ionized path to a charged cloud. If a tower is at that spot the path is shortened by tens or hundreds of feet but given the typical path distance is 10,000-20,000 feet this is but a drop in the bucket.
 
Alternative Antenna Grounding Techniques  
by K1NVY on February 3, 2011 Mail this to a friend!
Chuck...If this was a homework assignment given to me by one of my students, I would have circled "Mhz" in red and written "it's MHz not Mhz".
 
RE: Alternative Antenna Grounding Techniques  
by AC6RH on February 13, 2011 Mail this to a friend!
It is my understanding that lightning rods *do* attract lightning. If the Earth has one charge, and the air mass has an opposite charge, anything that is at the same potential as the Earth that is protruding high into the air, closer to the charged air mass, stands a greater likelihood, by closing the distance between the 2 charges of being struck by lightning than the flat ground below.

I could be wrong, but I believe electricity prefers to leap across a shorter path when such a path is present.
 
Alternative Antenna Grounding Techniques  
by WA9ENA on March 1, 2011 Mail this to a friend!
If nothing else, this article has certainly stimulated some discussion on the topic of lightning protection and damage prevention. I do take issue with one statement made within the article and also with a concept: 1) The statement issue arises over the comment about a dipole only "...having one side grounded". Since a dipole is a balanced antenna by design, NEITHER side should be considered as "grounded". This is literally true if the antenna is fed with balanced line (no coax), and is true only for DC when fed with coax but the "ground" connection is at the far end of the cable and might be on the chassis of the very equipment that is supposed to be protected.

The concept issue arises from the fact that some readers may actually believe that implementing this scheme (with suitable antenna types) will provide adequate lightning protection. In some cases, that might be true. (I do agree that it may lower static-induced noise levels.) However, what is not considered is that in most fixed-site installations, there can be anywhere from maybe 25 feet to hundreds of feet of cable between the ham shack and the antenna. Unless there is a coaxial cable protection device properly installed and grounded near the shack end of the cable, a direct or near-direct lightning strike to the antenna's support structure (mast, tree, tower, etc.) will almost surely produce a gradient field around the area of the strike. When the EM lines of force within that field cut across the cable, very large currents will be induced into that cable and those can, and will, do damage to the equipment and other items within the shack. While the advice about disconnecting coax prior to storms is very good advice, it is sometimes not possible or people forget to do it. (Besides, what do YOU do with the disconnected cable end? It had better not be inside the shack.)

A short series of articles in "QST" back in 2002 provided a very thorough description of the proper techniques to employ for avoiding or minimizing damage to the shack and equipment from lightning strikes. The bottom line: Be certain that EVERY I/O line associated with the shack AND the host building (house, usually) is protected, and that there be a solid grounding system in place.

I have more than a dozen coax lines, plus power, telephone, remote switch and rotator control lines, as well as external TV antenna cables all entering my house, at opposite ends, I might add. I buried more than 200 feet of #2 AWG stranded bare copper and sunk in 13 ground rods (with CadWelded[c] connections) when the house was built in 2000. I have 3 towers, two of which are spaced out at 50 and 200 feet from the house (with cable runs to match) All towers have ring grounds around the base. Every one of the listed interfaces has a protector, most of which are contained in weather-proof aluminum boxes mounted on the exterior of the house and which are tied directly into that ground ring. The entire system is configured in a unipotential "star" arangement as detailed in MIL-HDBK-419A. Overkill? Let's see...

I have taken 2 direct lightning hits to my 100 foot main tower and antenna structure. Both times, one or more antennas on the tower were either vaporized or damaged, and remote switches have been welded and coax cables arced out and damaged beyond use. During the first direct hit, I was actually on the radio that went to the topmost antenna (2m/70cm dual band vert) that got blown to bits and am still here to tell about it because the ground system and protectors all did their jobs as designed. NO equipment in the shack or house was damaged. NO circuit breakers tripped, NO GFIs tripped. I was on the radio because I was handling storm-related emergency communications at the time.

A second strike hit a year later. I was not on a radio at that time, but only 1 piece of shack equipment was damaged - a 2m FM rig had its receiver input blown because the coax protector had to be specified to handle the transmit power level, which sets the protection level higher than many receivers can withstand. Otherwise, no damage again to computers or appliances within the house, and NO tripped breakers or GFIs within the house.

My antennas span 160m thru 70cm, and there are lots of them. Disconnect is not an option because there are so many and also - what good are radios that have no antennas connected during emergencies? Cost of this protection system? Roughly that of a moderate-price HF transceiver. Piece of mind? Priceless!

Disclaimer: I have no vested interest in any provider of protection devices - I am just an EMC engineer who has been involved with various aspects of lightning protection for more than 40 years.

73, de Dale, WA9ENA

 
Email Subscription
You are not subscribed to discussions on this article.

Subscribe!
My Subscriptions
Subscriptions Help

Related News & Articles
Your First HF Dipole
Get Rid Of That Lossy (Lousy) T-Match


Other Antennas Articles
Get Rid Of That Lossy (Lousy) T-Match
Your First HF Dipole
Smaller Backyard, Revised 40-Meter Beam!