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Deadly Eyes
| | Posted on Saturday, June 22, 2002 - 11:28 am: | 
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Dirt varies, not all dirt is the same.
The most perfect ground is of course the surface of the ocean. The very last place you would want to place your antenna support structure is over rock or sand. Fortunately most of us live somewhere in between these two extremes.
The ability of any one's antenna to perform to its best and specs are affected by the ground. A ground that is bad is lossy and causes the performance to decrease. A good ground (man made or otherwise) helps performance.
If your antenna has a good match but still you cannot get that same umph you might try adding a ground wire system at the base of your antennas supporting tower or telescopic pole.
Commercial Broadcast systems bury hundreds of quarter wave length wires in an equal spacing around their antenna supporting structures to create the best possible ground field. Fortunately you do not have to bury hundreds. BUT if you put out/bury just beneath the surface just 4 quarter wave length radial wires, space out equally in a circle all attached to the base of the antenna you will probably see improvement in your signal at the receiving end. Bury 8, 12, 16, etc quarter wavelength radials. The more you bury the better and more efficient your antenna system will become.
Only one sour grape, you will reach a point where adding more radials to your ground system will start to help you less and less. At this point you have to decide if all that extra wire and digging is worth the little you gain.
What is that you say, you cannot run a complete quarter wavelength piece of wire. Well do not worry. Any wire of any length used will be of help. If you cannot run a full quarter wavelength then use eighths wavelengths. Run whatever length you can. Run as many as you feel is practical and productive. Every little bit helps.
When making your ground system you will of course need certain materials. Check with our good host, Coppers, to see if they can help you with your needs. |
jyd
| | Posted on Saturday, June 22, 2002 - 9:48 pm: |
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try this my antenna is 2 feet from a large swimming pool 20,000 gallon.not as big as the ocean but it helps reflect power |
Alsworld
| | Posted on Sunday, June 23, 2002 - 1:32 am: |
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Deadly Eyes,
first off, great information. However, here are some questions. How does the heighth of the antenna above ground compare to the radials? For instance, I run an IMAX 2000 5/8 wave omni approx. 39 feet to the base, 63'-64' to the top above ground. At that heighth, would radials really make a difference?
Second question is grounding. I currently have the base of the antenna grounded to the antenna pole (at the top), which is in turn double grounded to two 5/8" 8 ft solid copper grounding rods (at the bottom). Unfortunately, my soil is pure sand (too close to the beach). I have a third like grounding rod I have not installed yet. I realize sand sucks as a ground but I'm stuck there.
Living in Florida, lightning is my main concern as performance seems okay, but any performance tips I will listen to. Obviously I unhook my coax from my equipment when storms threaten, but sometimes that is not always possible (especially here in FL). My coax is more expensive than my antenna so I would prefer having it shatter (the antenna) then trash everything. If you are unfamiliar with the IMAX 2000, check out the "Subscriber Preview" section of this forum and look at the review.
Curious as to your thoughts.
Alsworld |
DeadlyEyes
| | Posted on Sunday, June 23, 2002 - 9:38 am: |
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Re Al....
You did not say if your limits of height were set by CB or Ham regs. I will reply to both....
If you are CB restricted then the height would should not make too much difference because the legal height is 60 ft from top of antenna to ground or 20 foot over supporting structure. When you are this close to the ground any linkage between the antenna and the ground should be pretty easy.
If you are Amateur Restricted to 200 feet and do not have airport restrictions on height then height becomes a little more complicated. The height of the antenna above ground has more to do with reflection. The closer to the ground the greater the vertical angle of transmission. Your signal goes increasing vertical rather than horizantal. If you are looking for local then you are in good shape. A high angle of radiation antenna such as a Lazy Loop radiates its signal strate up and its bounce only covers a between 100 and 200 miles rather than thousands. Some people will tell you X feet or Y feet or multiples of Z feet. A good rule of thumb is as high as is practical. Having said this also take into consideration: lightning, lighting regs and of course the pain to bring it down and back up to fix it.
An antenna is a form of an electrical circuit even though it does not look like one to the eye. So the less the ground resistance the better the circuit will function.
As to grounding. Perform a test. Run 8 quarter wave ground wires equally spaced in a circle and just lay them on the surface. Temporarily connect them to the grounding rods. Over the course of a couple of days check out the performance of your system. Is your signal a little better? Is your SWR less strained? Has your distance of transmission/hearing increased a little bit? Generally overall is it better? The ultimate decision of is it worth a permanent install job will in the end be up to you.
Some Amateur Ops would dig up their entire back yard to gain even the smallest of advantages. I on the other hand say naaaaa, they hear me/good enough.
Good luck
DE |
DeadlyEyes
| | Posted on Sunday, June 23, 2002 - 9:46 am: |
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Re jyd....
Just Curious. Have you noted that your best receive and transmit has taken place in the direction of the swimming pool? |
Galileo
| | Posted on Sunday, June 23, 2002 - 10:34 am: |
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Im running 2-8 foot 5/8th's ground rods, (courtesy of the electric company) 4 gauge wielding cable running from the base of the antenna The rods are in an area where the drip from the air conditioner keeps the soil moist..My mast is connected to the ground rods by double zero gauge wielding cable.I have 2 more rods I plan to install.All rods are connected using hard drawn copper...At some point I would like to bury some radials just to see if it makes a difference..Should I ground the shield of my coax before it enters my building???? Thanks, Tom Shaw |
DeadlyEyes
| | Posted on Sunday, June 23, 2002 - 11:23 pm: |
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Re G....
In reply to grounding of coax directly, you should not have to ground the coax in order to gain best signal reception/signal transmission. But you might want to for other reasons--see below. But first look at where you screw in the connector in back of your radio and then at the grounding screw. You will notice that they, if your radio is like most radios are on the same stamped out sheet of metal. So you should not have to ground out the coax before entry for the purposes of reception.
HOWEVER, having said this you might want to put in line with your coax on the outside of the building before you enter your radio room a lightning grounding block and run this to the ground systems grounding rods using some sturdy wire. A lightning grounding block is just like a spark plug for an automobile. When the lightning goes down your coax it senses a less resistive, more direct route thru your grounding block. It goes to ground directly rather than send 100% of all that juce thru your radio.
ONE last thing, Equipment Insurance Policies. Perhaps your home insurance covers your radio equipemen. Perhaps it does not. You might ask your insurance person to find out.
If you are a licensed amateur and are also a member of the ARRL you can get insurance on all your equipment from the ARRL.
At any rate you might want to look into equipemnt insurance to specifically cover your radio equipment.
PS on the grounding rods use the longer rather than the shorter if given a choice. I know it is a pain to drive those longer ones even if you use the water in the hole trick. But the longer one will be the overall better choice. An 8 foot rod will fit the needs quite well.
PPS One last thing, remember my comment in the above post. There is a point at which adding more ground wires will begin to yield smaller and smaller benefits. When you stop is up to you.
good luck
DE |
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