A good ground is one of the most essential parts of a good HAM station. There are various reasons for this statement. First and foremost is for the safety of your family, home, and HAM equipment.
Lightning NOT ONLY KILLS HAM radios but often starts house fires - jeopardizing the safety of your family! A protruding antenna or tower into the atmosphere dramatically increases your odds of a
lightning strike. Statistically however, most lightning damage comes from the AC power or telephone lines running into your home.
An understated fact of significance to HAM Radio is that a good ground WILL increase receiver sensitivity and transmit propagation. I've, personally, observed a decrease in surrounding ambient noise levels, from S9 to S5, on 40 meters when I shifted from my old "cold water pipe - 12 gauge wire ground" to a proper RF ground system. HF antenna(s) work BEST when they work against a proper counter-poise ground reference.
Good RF grounding is as mis-understood and as difficult to understand as phenomena of impedance. Both are very real, hard to measure, and cannot be tangibly seen in operation. The term that is used in RF grounding is "skin effect." In a ground system the majority of electrons run along the surface (or skin) of the conductor. A good RF ground has the least amount of resistance to electron being conducted to ground. This is obtained by having the most amount of conducting surface area, that is practical. The goal of a good RF ground system is to obtain as little resistance as possible from the antenna/tower to ground and the radio to ground. Thus the more conductor surface area the more ground path conductivity.
A good ground system measures less than 12W
from radio to ground. Typical, cold water pipe grounds will measure >35W
and that's if the water pipes are NOT PVC. Making this measurement is very difficult and most HAMs do not have a Megger instrument to make the measurement. Some education, a well planned out, and properly installed ground system is typically the best most
HAMs can afford and accomplish. That's were this paper will attempt to assist you by giving examples of reasonably good RF ground systems that are within the economical range of most
HAMs.
A few items need to be contemplated before deciding on how to install your RF ground system.
a. You need to consider your budget and the amount of effort that you are willing to give in installing a good RF ground system. It is NOT to your advantage to be too cheap and lazy - or you might as well just use the cold water pipe. Then be prepared to buy new equipment when you get your first lightning strike.
b. Dissimilar metals (as it pertains to electrolyzing/galvanic action) can pose a significant problem to the systems longevity and minimizing maintenance issues to your ground system. One rule is NEVER connect copper to galvanized or aluminum towers - use a stainless steal interface between the two metals with a stainless steal clamp, bolt, washer, and nut!
c. Copper oxide (the greenish copper corrosion) is NOT conductive! Eventually compression clamps WILL allow corrosion to migrate into joints causing a reduction in conductivity and increase the connections overall resistance. Weld or solder ALL joints, when possible, this will ensure long life and maintain stable good conductivity between connections! If a stainless steal clamp is used a conductive grease is required to minimize connection moisture degradation.
d. Eliminate ground loops and multi-point ground connections when possible. A HAM shack ground loop gives lightning another path to your equipment. Always use a single point ground between the interior and exterior of your HAM shack!
e. Run your coax/hard-lines to the base of your tower or antenna mast and directly connect to the coax/hard-line shield clamps to the tower/mast base. This will allow the lightning to get as close to the actual ground connection before attempting to enter the house. When creating a drip bend in coax/hard-line use a minimum radius of nine inches for the curves.
g. Grounds rods or other grounding pipes MUST reach below your local areas permafrost layer to remain active year around. You can easily find this level by checking your local plumbing building codes. Typically, in central Wisconsin the minimum depth is six feet. The ideal grounding situation is in having your ground system make physical contact with the water table, however, this is not very practical.
This document gives examples of two scenarios for a good RF HAM ground system:
First a house mounted antenna ground system;
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Second a tower mounted antenna ground system.
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Grounding Rods vs. Pipes
Due to economics and the effort required to drive rods I've taken another approach in
lieu of rods. (Besides four foot rods are worthless as they do not make enough soil contact for an adequate safety ground much less an RF ground.) I use ten foot pieces of 0.5" copper PIPE fitted with a brass hose fitting. I purchase a brass hose fitting from a local hardware store and solder this fitting to the end of the copper pipe. This allows me to attach a garden water hose and easily hydra-drill the copper pipe into the soil. No mallet or "T" post sledge for me.
I dug a one foot square deep hole in the ground where the ground pipe is to be drilled. I drilled the pipe into the ground until the pipe top was 6" below the surface of the ground. This allowed working room to solder the copper tubing and then cover the hole making it invisible to all and your lawn mower.
Ground Conductor Copper Buss-bar vs. soft Copper Tubing
Again, due to the economics and availability of copper buss-bar material I found the costs to be prohibitive to a normal HAM's budget. Instead I use soft copper tubing that is easily obtained at your local hardware stores. The trade off is the amount of surface area the copper tubing will have in comparison to copper buss-bars. I highly recommend that you use ³
0.5" copper tubing for short runs, i.e. £
10', or as your budget will allow - but attempt to keep the conductor surface area high as near to 1.0" copper tubing as you can afford. Remember, the more surface area the better the ground conductivity!!!
I use soft copper tubing for practical reasons - ease of use. Where a soldered or clamped connection is to be made I hammer the tubing flat. Then using Vice-GripsÔ
I wrap the flattened tubing very tight around the copper ground pipe/rod and make a good soldered connection.
The copper tubing is buried at least 6" deep. This will keep you from hitting the ground system with the lawn mower or becoming a trip hazard. The buried copper tubing is also part of the energy dissipating ground system. In using buried interconnect bare copper tubing the whole "ground system" conductivity can be increased when watering the lawn as the near surface soil conductivity will increase. A HINT during contesting.
Ground Plate
This item can be controversial to some as few HAMs want to mount or put a fair sized hole in the side of their house. The ground plate is a solid barrier to possible
lightning entering your house via your coax/cables. Also this ground plate is the fundamental item that creates your "single point" ground and gives you the proper place to install other protective devices, i.e. rotor cable protector, telephone line protector, etc.
I recommend that the ground plate be made from ³
0.125" stainless steel the dimensions depends on how many protectors need to be mounted. I selected stainless steel as it eliminates the dissimilar metals concern and allows direct copper attachment.
If you do not want to mount the plate in the house wall then mount the plate ON the house perpendicular to the wall very near to the coax HAM shack entrance. Run the coaxes on one side of the plate, clear of the house entrance, then from the opposite side of the plate run the cables and internal station ground conductor into the house. Connect the ground plate to a ground pipe that is within three feet from the house. The closer the connection between the nearest ground pipe and the ground plate the better the conductivity - I would use 1" or three 5/8" copper tubing pieces between these two points and then reduce the copper tubing size to the other ground pipes!
The ground plate is for mounting bulkhead surge/lightning protectors. The best protector and the ONLY one that I recommend and use is the PolyPhaserÔ
type! See Appendix A. This is your last and best protection item. The PolyPhaser blocks and redirects the surge energy into your ground system. This also means that you need enough of a ground system to dissipate the initial energy and the ringing energy. See diagrams.
Ground Pipe/Rod placement
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One of the biggest issues facing you is HOW MANY ground pipes/rods should you install? This is hard to determine as it is based on soil conduction, how potent is the lightning strike, how much room do you have, and what can you afford. If you look at a commercial system they have multiple ground radials (seven or more) each 32 feet long and four ground rods on each radial. Some of the ground rods can be sunk as deep as 40 feet. Well this is NOT in my budget or in most
HAMs!
Obviously, the more ground radials and ground rods the better. I try to run at least three ground rods in a non-tower HAM shack. One directly outside the HAM shack at the coax cable enterance point (the shack ground), and at least two more ground radials with ground rods at their ends
seperated by at least eight feet from the shack ground.
The tower increases the potential of a lightning strike so in addition to the above scenario two or more rods should be placed just for the tower. One rod near the tower base and the other rod eight feet away. Use 1" or two 5/8" pieces of copper tubing between the first tower rod and the tower.
The goal of a grounding rod is to make contact with the water table. Falling short of that it is to dissipate as much energy as possible. By driving the ground rod directly down attempting to traverse as many soil layers as possible so energy can be dissipated into these various soil layers. Some soils conduct better than others - dry sand being the worst followed by hard clay. But a hard clay layer may have some amount of water riding on the clay seeking penetration points.
Placing the ground rod at a 45°
angle can increase to overall length of the radial and allow some energy to be dissipated. Angled ground rods are often used in rocky soil.
Interior Ground connections
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The interior ground conductor is just as important as the exterior ground system. I run 5/8" copper tubing from the ground plate along the mop-board behind the HAM station desk. Using old RG-8 or (better) RG-9913 coax cable I strip off the outside plastic coating and expose the braid. Measure from the mop-board conductor to the back of each piece of equipment to be grounded. Keep the braid ground strap as short as possible. Strip the braid from the inside coax conductor. Solder the braid to the mop-board conductor and on the opposite end either heavily tin the braid and place a hole in the tinned area or solder an eyelet lug. Connect the braid to the radios, antenna tuner, computer, etc. Most radio equipment comes with an extruding bolt, washers, and a wing-nut - if not find a good chassis screw to place the braid with washer beneath.
The goals is to have an effective ground connection with short ground straps and to keep a clean unobtrusive appearance to the HAM shack.
Special Editors NOTES:
a. Watch out using push-up masts. They may NOT have good inter-section conductivity. Additional ground strapping between sections may be required.
b. Use conductive grease / moisture prohibiter under all exterior ground connections. Eliminate poor conductivity before it happens.
c. Use stainless steal clamps, bolts, washers, and nuts on all exterior ground connections, especially where making contact with copper.
d. The frequency of typical lightning is between DC to 1 MHz.
e. I did not cover grounding guy wires due to the fact that most installations use one or more insulators on each guy wire to keep the wires from becoming parasitic conductors causing RFI concerns. Or many HAMs use the guy wires (with judicious insulator placement) for make shift inverted "V" antennas. So grounding of the guy wires defeats the ancillary intent/antenna use.
f. Any conductor that could carry lightning should not make any bends smaller than an eight inch radius - the larger the radius the better. This requirement holds special significance to the connections between the tower, mast or ground plate!
g. Additional reference material sources:
Military HDBK-419
1" $3.69 / ft. **
0.75" (3/4) $2.19 / ft. **
0.625" (5/8) $1.09 / ft.
0.5" (1/2) $0.69 / ft.
0.25" (1/4) $0.39 / ft.
4 oz. FG 60500027 $15.00 GOOD
