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many discussions about grounds

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arkieguide

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c. RF ground.
This is required only for certain types of antennas-- ones which require current flow to ground to complete
the antenna circuit. An example is a quarter-wave vertical. One wire of the feedline connects to the base of the antenna, and the other connects to ground. The connection to ground has to have a low RF resistance, or you'll expend too much of your power heating the ground. A few radial wires will provide a moderately low loss connection. A ground rod will help a little, but the RF resistance will be high, resulting in quite a bit of loss.
Chapter 8 of the ARRL Antenna Book shows the approximate trade between resistance and number of radials. If your antenna is much shorter than ¼ wavelength, you'll need many, many radials to get reasonable efficiency. If it's longer, you can get by with fewer. A ½ wavelength base-fed vertical needs only a very modest ground, and a ground rod is adequate. The requirements for various other end-fed
antennas depend on their length. If you use a "complete" antenna like a dipole or a ground plane (that is, one that doesn't require your feedline to connect to ground), you don't need a RF ground, as long as you keep common-mode currents off your feedline. A "current" or "choke" balun is most commonly used for this.
 

TheSpaceMann

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ARRL

c. RF ground.
This is required only for certain types of antennas-- ones which require current flow to ground to complete
the antenna circuit. An example is a quarter-wave vertical. One wire of the feedline connects to the base of the antenna, and the other connects to ground. The connection to ground has to have a low RF resistance, or you'll expend too much of your power heating the ground. A few radial wires will provide a moderately low loss connection. A ground rod will help a little, but the RF resistance will be high, resulting in quite a bit of loss.
Chapter 8 of the ARRL Antenna Book shows the approximate trade between resistance and number of radials. If your antenna is much shorter than ¼ wavelength, you'll need many, many radials to get reasonable efficiency. If it's longer, you can get by with fewer. A ½ wavelength base-fed vertical needs only a very modest ground, and a ground rod is adequate. The requirements for various other end-fed
antennas depend on their length. If you use a "complete" antenna like a dipole or a ground plane (that is, one that doesn't require your feedline to connect to ground), you don't need a RF ground, as long as you keep common-mode currents off your feedline. A "current" or "choke" balun is most commonly used for this.
What would be the approximate dimensions for an 11 meter ground mounted vertical?
 

JayMojave

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YO: 234 divided by the frequency in MHZ = 1/4 wavelength in feet. Or
2808 divided by the frequency in MHz = 1/4 wavelength in inches.

So for channel 20 lets say, 2808 / 27.205 = 103.2 inches for the element lengths.

You can to do a slight adjustment in the element lengths to get the lowest SWR with a SWR meter or antenna analyzer. But the 1/4 wavelength antenna is a very broadband antenna that will work over all the channels and then some with no adjustment.

Jay in the Great Mojave Desert
 
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prcguy

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When you get ground radials very close to the ground or laying on the ground they get completely detuned and are no longer resonant, so lengths are not critical. Then you have a ground loss problem where if you take say a ground plane antenna with three or four radials and measure its performance 10-20ft off the ground, it will loose a lot of performance when the radials are laying on the ground due to ground (earth) losses. Its like putting resistors between the ground radials and where they connect to the ground of the coax.

To overcome this you need a lot and I mean a lot of radials like more than a dozen and preferably 32 or more laying on the ground. Its actually easier and better to cover the ground with chicken wire or hardware cloth to make a large non resonant surface area below the antenna when its ground system is laying on the ground.

A typical 1/4 wave high AM broadcast tower has 132 ground radials connected and they are at least 1/4 wavelength long and many stations that have space will use 1/2 wavelength long radial wires on the ground. At 1Mhz these wires will be 234ft long each for 1/4 wavelength or 468ft long if they are 1/2 wavelength and the diameter of the radial field would be almost 1,000ft across for 1/2 wave radials. 132 radials 1/2 wavelength long at 1MHz would be 11.7 miles of wire. That's a lot of wire and they do it for a reason.

After you put your antenna on the actual ground and overcome ground loss problems with a field of chicken wire under it, you will have the simple problem of the antenna being very low when talking to locals on CB and using a much simpler antenna higher up will extend your range considerably being more line of sight compared to the antenna sitting right on the ground and blocked by buildings, etc.

The ground mounted antenna with really good ground plane laying on the ground should do great for skip but its a lot of effort for very little payoff in my opinion. Hams do ground mounted antennas all the time but mostly for much lower frequencies than CB like 3.8MHz or 7.2Mhz or even 1.8MHz where the antennas are large and more difficult to mount on roofs, etc. Plus the ground radial needs are huge for an antenna at 3.8Mhz where you would need at least three or four wires 65ft long each running in different directions if that antenna were mounted on a roof.

Besides all the great published data on the subject, I've done a lot of experiments with ground mounted verticals with radials on the ground and measured performance starting with only a ground rod, then four radials, then eight, 12, 16, 24 and finally 32 and there is a huge difference between no radials and 32 and a very noticeable difference between just a ground rod and four radials. You do get to a point of diminishing return after about 24 but if you want the last word in performance you keep going and put more down.

After its all said and done, compare your ground mounted vertical with a boatload of radials to a simple dipole up high and you will ask yourself why did I do this? On the lower ham bands a simple dipole will usually outperform a ground mounted vertical every time and its a whole lot easier to install. For CB I suspect something like a Hy-Gain Penetrator at 18ft or 32ft height to the base of the antenna will greatly outperform any vertical antenna you can assemble on the ground with a lot of radials on the ground.



What would be the approximate dimensions for an 11 meter ground mounted vertical?
 
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JayMojave

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Hello PRCGUY and All: WOW great posting prcguy, well done sharing all that with us.

One of our local low band hams passed a few years ago, and I and a friend took down his two towers that had massive ground plane wires from each tower connected to the base of the towers.
This guy was a big time 160/80/40 meter operator and he had written articles in the ARRL Handbooks, as how to feed and match the towers for a vertical antenna for the low bands. Earl is very much missed for his technical knowledge.

The elevated 1/4 wavelength antenna with say 4 ground plane elements, is a easy and quick antenna to make. And doesn't always need to be adjusted for min SWR. But while tuning a 1/4 wave ground plane on a antenna analyzer one day I had seen the vertical element and the ground plane radials has separate nulls or min SWR frequencies.

When the ground plane elements were length adjusted to the same null or SWR min, the 1/4 wave ground plane has a significantly wide band width. The ground plane elements were mounted at a 45 degree down angle from level Horizontal. Food for thought.

Again great posting prcguy.

Jay in the Great Mojave Desert three digit heat wave here for the last few weeks, lovely place to be from
 
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