I agree with the paper except for one thing. I don't think it makes any difference whether buried radials, or radials lying on top of the ground, are bare or insulated.
Insulated wire will last longer because the plastic insulation protects the copper from corrosive minerals in the soil.
Besides providing the "mirror" for the image antenna, you can think of the ground radial system as a shield to isolate the radiating antenna from the lossy earth. It follows logically that the farther away the ground plane is elevated from the earth, the more effective the shield will be, and fewer wires will be needed. Also, by burying the radials, you have a thin layer of lossy earth between the radiator and the ground plane, so burying the radial wires partially defeats the whole purpose of the ground plane. However, the loss is negligible if the radials are buried no more than a couple of inches into the ground. The only purpose for burying the radials is to protect them from damage by surface traffic such as humans, animals, lawn mowers, vehicles, etc.
I have a pre-WW2 ARRL antenna book in which they recommend burying the radials a couple of feet into the ground; I don't know if that was a typo and they might have meant inches. Besides reducing the efficiency of the ground plane, imagine how much work it would take to bury 120 quarter wave radials on 160, two feet underground.
Hi Don, thanks--I want to apologize for the size of the file. I am going to try to work out a new way of scanning these things so the resulting file is smaller.
I like this paper only because my inverted L radials are all insulated no. 14 solid, laying on the ground (except by now they have sunken in a bit) and like any other antenna phool I'll grasp at anything that will make me feel good about taking the lazy way out.
But seriously, I know some b/c stations bury to prevent theft in addition to the reasons you gave. There's one guy in the industry who recommends putting them down _five or six feet_. I can't remember what they do to get them that deep but his reasoning is that you'll never have to worry about copper theft when they're that deep. I know ground penetration of RF varies with frequency--I guess the lower the frequency the deeper the penetration (which must be why those submarine commo systems are so low) so 5 feet deep might be okay for under 1 MHz but it might not work for hams, as if a ham would do such a thing. Oh, I guess another advantage to going a bit deep up here in the north is to prevent ground heave from pushing them up during freeze thaw cycles.
Anyway, there are a zillion papers on radials but this one had an interesting point I thought and as far as I know had not been widely circulated so I thought I'd add it to the radial signal to noise.
73
Rob K5UJ