This is probably over-kill, bit you get the idea for a Part 15 ground mounted system.
That is a gaphically very good radial example just right for Part 15.
The only added thing to use would be some Radial Anchor Pins from Ross Radio, as originally suggested by PhilB.
I lucked into an E-bay sale and have 375 pins at a very low price.
The pins came with all kinds of goodies: two instruction sheets, a QSL card from KB8NTY, and a CD that I guess contains a video tutorial,
www.rossradio.net
Take a good look at the ground there....nothing but sand, small rocks, no plants or grass, etc. That's about the worst natural ground I've seen. Looks like moon surface...nothing will grow there, no good soil. Therefore the natural conductivity of the ground as shown is probably near 0....meaning pretty serious artificial ground has to be built, as much as you can do. Many 'standard' AM bcb radio antenna towers have 120 1/4 wave copper strip radials. That's why those older station antennas are usually in the middle of a cleared field large enough to accommodate the ground system. If you see one you know has gone dark, you might enquire about the current property owner and see if you can get permission to pull up the copper...it'd be worth the effort.
Ground radials do not need to be much longer than the antenna is tall. A shortened antenna with loading coils will have a more compact “near field” where the majority of the antenna field is. The ground needs only reach out as far as the near field extends. Field intensity drops off with the square of the distance from the base of the antenna.
This is an argument I have made for years.
Field intensity drops off with the square of the distance from the base of the antenna.
That is a commonly-written and accepted belief, but it applies to radiated power, not field intensity. And only in the far field.
Field intensity is a voltage, and it is inversely proportional to distance. The groundwave field at the end of a 200-meter path from the transmit antenna is half that of a 100-meter path, other things equal.
So are we saying that for a ground mounted transmitter with a 3 meter whip the ground radials should be 328 feet?
Below is a clip on this topic from a "benchmark" experimental study about buried ground systems published in the Proceedings of the Institute of Radio Engineers in 1937.
It shows that a monopole of about 6 degrees in physical height* will benefit from radial wire lengths much longer than 3 meters when used with 15 buried wires -- which might be about the number a Part 15 operator would install.
* describes a 3-meter monopole at the high end of the broadcast band
Just FYI, I have found that most standards-built AM radio stations have used a 1/4 wave tower radiator and 120 @ 1/4 wave buried copper strap radials fanned out evenly at the base, with everything bonded to each other and any number of deep ground rods, Some have capacitive hats, particularly in the lower end of the band.
Here in Friday Harbor, the commercially built LF aviation NDB is a 50' radiating tower with a 6-element capacitive hat and 12 ground radials laid out from the base, the same length as the antenna height. Professionally tuned up, 25 watts gets out very solid to 35 statute miles.
There are very few of these in operation anymore, but this one is new, to replace one that was brought down to make room for more airport building construction. Why didn't they just move it, you ask (nothing mechanically wrong with the old one)? Because neither the FCC nor the FAA is willing to issue permits for startup NDBs (it's old technology).
Which means if they wanted to retain its existance, it could not be shut down (service interrupt) for any significant amount of time, so moving and rebuilding would have taken too long. Thus, they had to build a new one, leaving the old one running, get all the wiring, tuning, paperwork, etc., etc. all in place, then basically throw a switch to transfer the workload. Then and then only could they tear down and move the old system off its site (the site for the new one is much better aligned with, and off the end of, the runway).
A lot of blab, but some new folk here might not have seen the post from a few years ago, plus I've had some more insight about the situation since then. The HAM radio guys now have the tower...plan to mount several repeaters and digital gear capable of connecting to world-wide nets on it.