Let me clarify my request for comments.
I am going to enter some mobile shoot out contests so I am looking to increase the radiation resistance of the entire system.
The only possible way to increase radiation resistance is to make the ampere-feet area of the antenna larger. The ground won't do it. Two things do that;
1.) Top loading as high up as possible, especially with a hat way up high.
2.) A taller vertical.
So once these items are done all I can think of is to improve the counterpoise. I consider the jeep to be basically a vertical antenna and if you add radials to a vertical you improve the efficiency.
A radial works because it spreads the current out, and the electric and magnetic fields out. If you put 500 feet of wire in a shoebox near the Jeep body, you have a Jeep body with a shoebox on it. The difference is insignificant. You did not expand the area.
Thus I am thinking about how to improve the vehicle have of the antenna. I could add some hamsticks to act like radials on the bottom of the screwdriver antenna which I will try because I have them available, but I am wondering about these Petlowany coils to try also.
With a Hamstick sticking out horizontally, you add a inches of effective length to the Jeep. I doubt you will have a measurable difference unless you start getting directivity.
So its not that I dont think my installation is having problems but I am looking for methods to improve the system so that I can squeeze out some efficiency. Also if the coil does work I can mount it to the spare tire and harden it for a more permanent installation.
The objective of a ground or counterpoise is to spread the fields out away from the antenna so they are not concentrated in one small area. How will a coil on the spare tire do that?
To spread the fields out, you would have to have things sticking out horizontally away from the Jeep body. Pulling a trailer will work. Or, if you want the Jeep to be a better ground, park it on a F250 Supercab with 8 foot bed.
If coiled up radials would work, broadcast stations and Hams would be using them everywhere.