Grounding the Shield?

[chrissim]

Hello:

This is confusing me to no end: grounding the shield. I just received my tech license and thought I'd have a go at 10 meters. The Antron 99 is supposedly a decent antenna for just such an exercise. I happen to have one in the garage that's collecting dust.

Some say to use radials, some say don't bother. I've also read where some say to simply lay them out at the bottom of the antenna, and some say to lay them out and ground them at the shield. This is a concept that has befuddled me for some time. If I consider what it means to ground at the shield, that would imply that I would need to strip the coax and use the braid in some fashion and connect it to the radials. This doesn't seem logical. So then, in laymen's terms, what does grounding the shield actually mean?

The best I can come up with is that one leaves the coax intact and uses a ground block. Certainly I wouldn't strip cable for this endeavor...

Thanks for your patience.

 

[DisasterGuy]

Bonding or grounding the shield of coax is more a standard practice for the purposes of electrical grounding than it is in relation to the RF groundplane (ie: radials). You should be bonding the braid to ground at the base of the mast as well as just prior to entrance into the building. This is part of the basic site standards for every manufacturer that I am aware of including Motorola, Harris, etc. The process for doing this does involve removing some of the outer jacket and ultimately resealing the area. Most cable manufacturers including Times Microwave and Andrew offer kits specifically for this:
Cable Accessories, Grounding Kits | TESSCO 800 472 7373

 

[WA0CBW]

Another method to "ground the shield" is to use a UHF feedthru. The feedthru(s) can be mounted to a copper buss bar. Cut the coax and put a connector on each end. Be sure to waterproof the connectors and feedthru. The Buss bar is then grounded to your external ground. (Dont forget that this ground bus needs to be connected to your main house electrical ground). DX Engineering makes a device that will mount to your ground rod. You can also use the coax ground kits mentioned by 'DisasterGuy".
Don't confuse a "ground plane" with an electrical ground. Although they connect together they both serve different purposes. A ground plane is a field of wires radiating out in a circle from the base of a ground mounted vertical antenna for example. This ground plane connects to the shield side of the coax and the center conductor connects to the vertical radiating element. The ground plane and the vertical radiator are insulated from each other. A ground plane does not require a ground rod. But your ground plane should connect to the master ground and your house electrical entrance panel ground. You can simple extend one of your radials to make that connection. It should probably be a little heavier gauge than the rest of the radials. A ground plane can be on the ground or mounted just below the bottom of a vertical radiating element even if it is ten's of feet in the air.
Don't forget that the NEC (National Electrical Code) also requires the grounding of any metal mast that is used to support an antenna. If the mast ground rod is more than 20 feet from your existing main electrical ground then it needs to be connected together with a minimum #6 guage wire. If it is less than 20 feet then you can connect them together without the mast ground rod.
BB

Edit: The radials and the vertical radiating element may be connected together with a loading coil to match the impedance of the coax to the radiation resistance of the vertical radiator.

 

[LtDoc]

WA0CBW,
Wrong word. Change 'loading coil' to 'matching coil' and you got it. They are two entirely different things. They can be combined, but they still serve two unrelated purposes.
- 'Doc

 

[chrissim]

Thanks to all of you that replied. I appreciate it. What I have done in the past is to pound 10 foot ground rods to a depth of 9 feet, normally two of them, and connect them in series. One of my receiving antennas has a ground lug, and so I ground the lug to one of the rods. I then run coax in conduit in the soil which ultimately leads to my upstairs listening station via a feed-through panel. It's not practical to ground the station radios as I'm 21 feet above the ground.

Now that I'll be transmitting, I'll likely erect an OCF antenna about 75 feet from the house in the back yard using LMR 400. I intend to pound two or three ground rods,connect them in series, and use coax from the antenna and attach the coax to a polyphaser or transitrap which will be connected to one of the ground rods. Then from the polyphaser or transitrap, I'll connect the coax to lead to my upstairs feed-through panel and to the rig.

Considering that I am uncertain if this will be a permanent location for the antenna, or if I will be pleased with the antenna, I will likely forego the level of grounding under discussion. I can't imagine running some type of ground all the way to the ground of my house for this type of installation. Heck, what do amateur radio operators do on field day?

I should also mention that I have been heavily involved in reading as much as possible for the past several months before I decided to study for the exam, although I have seen references to grounding shields, this is the first time that I have been lead to believe that it is of utmost importance to do so.

As defiant as it may sound, I'm willing to bet there are many amateur radio operators who don't strip cable and buy the necessary kits to ground in such a fashion. I certainly believe all of you, but I would think that the testing material that the ARRL publishes would emphasize the importance of it. In fact, I'm looking at their guide as I type this and they claim that in terms of AC grounding, as long as the wiring has been done correctly in the house, I'm good. For RF grounding, they suggest a common bus to all equipment to keep everything on at the same RF voltage.

As for the Antron and my original question, that particular antenna is extremely temporary - buying kits and digging trenches to connect wires to house ground (a 150 foot run) seems extreme. I suppose I need to really get a better grasp on these concepts before I make a final decision. I've always been introverted, but joining the local amateur radio club will likely prove beneficial.

Thanks for your patience. Once I see, in person, what others are doing it will likely make more sense to me.

 

[WA0CBW]

Thank you Lt.Doc for correcting me. Me brain gets way ahead of me fingers when typing. For "chrissim" probably only a small percentage of hams go to these measures to ground their equipment. However for the money I have spent on equipment I don't want to have it destroyed by a lightning event. The reason for connecting all the grounds to a single point is to prevent "flash-over". Most lightning damage is caused by flash-over. This happens when one piece of equipment is at a different potential than another. This is evidenced by its ability to jump large distances. A mini lightning event occurs as the lightning jumps from one potential to another. If all of the equipment (including your house electrical and plumbing system) are connected to the same ground then the potential between pieces of equipment is near zero reducing the potential difference. In your case where your shack is on a second floor grounding becomes more difficult (and expensive). I tell people in my grounding seminars it is probably easier to move your shack than it is to properly ground your equipment from the second floor. As far as RF grounds go they are only needed for antennas that are not provided with ground radials such as ground mounted vertical antennas or some types of end fed antennas. Ground rods should be placed no closer than 2 times their length. No additional benefit is gained by placing them closer together. So 10 foot ground rods placed 9 feet into the ground should be no closer than 18 feet apart. As a Project Manager for Motorola for 20 years installing cellular and public safety sites I have seen my share of the damage lightning can cause due to incorrect grounding and lightning protection.
Good Luck which ever direction you choose to take!
BB - ARRL Technical Coordinator - Kansas Section

 

[DisasterGuy]

I have long believed that the FCC Exams should focus much more on issues such as bonding and grounding but I digress. If you want to understand how to properly ground and bond your station as well as all equipment I recommend reading these documents:

M/A-Com / Harris Standards for Site Grounding & Lightning Protection: http://www.repeater-builder.com/ge/lbi-library/t4618r3a.pdf

Motorola R-56 Standards & Guidelines for Communications Sites: http://www.radioandtrunking.com/downloads/motorola/R56_2005_manual.pdf

Both of these standards documents convey the methods that are used by any reputable communications shop for installations.

 

[chrissim]

Thanks so much for the information and help. I agree, more attention is needed in regards to grounding and the like. I will of course put more effort into grasping the concepts.

Been a huge help, fellas. Thanks again.

 

[cabletech]

Also, do not forget the NEC-(national electrical code), has in every chapter a section on grounding and bonding and a chapter (800) on communications.

This is used in every state.

Also, in some states there are requirements for electricions to take classes for maintaning their license that cover the NEC and state regulations.

Check with your state licenseing agency for contrators and see if you can find these classes and this will help to under stand the reg's.

Good luck

 

[nanZor]

For more info on the Solarcon / Antron A99 see this page, especially near the bottom where it goes into detail about the common-mode issues with this antenna:

End-fed Vertical and J-pole

Now you'll know why you are pulling your hair out.

 

[LtDoc]

WA0CBW,
FWIW, and it ain't worth much. I ain't NEVER made that sort of mistake! And I hope like #3\\ that I don't the same @#$ mistake again! I ain't gonna hold my breath though...
- 'Doc