The key here is "RESONANT ANTENNA", when we have a resonant tuned antenna (50 ohms impedance) and we use a matching 50 ohm coaxial cable and feed that into a matching 50 ohm radio, the laws of "Conjugate" are in effect and it wouldn't matter where you tested the SWR along the line, nor would it depend how many feet involved, there would still be a good SWR match with only slight variations due to natures pool of imperfections. The coax length should be just long enough to reach the rig.

For most cases when using a single antenna system with a 50 ohm coax feed ANY coaxial length will work providing the antenna is tuned properly at the feed-point of the antenna (where the coax attaches).

 

Grounding this mount makes little difference to the performance of the antenna. If the stick was being mounted to the center of a large flat metal surface (such as a roof or trunk lid) then a low resistance connection between the mount and the surface would matter. Why? This antenna is end fed which means that there is one lobe of radiated energy above the mount and (unfortunately) a matching lobe of rediated energy BELOW the feed point. A ground plane forces the energy in the lower lobe into the upper lobe and dramatically improves performance. Regretfully, there is no suitable metal surface on the JK that would provide an adequate ground plane. So the quality of the ground of the rear door only matters in that if it were poorly grounded it could be the source of noise in the receiver.

A better antenna for a mount like this is actually a vertical center fed dipole. It looks a bit like the firestick in that it has a fiberglass lower section with a radiator (wire) wrapped around it. The difference is that a coax cable runs from the base to the top end of the fiberglass tube where it is connected to the top whip and to the bottom radiator. This type of antenna requires no ground plane to perform well. Regretfully it would be very large for use on the 11 meter band.

I sure this will bring a howl of protests from many corners. But if in doubt go back to the books. The laws of physics are immutable.

 

While you may be right, I couldn't disagree more - in practice the ground does matter, at least when it comes to mounting on the tail gate.

 

Your absolutely right if your talking about a no-ground plane kit that uses the coax shield in the cable as counterpoise. If however you have a set up like most of us we have to have a good ground for counterpoise, it's equally as important as the antenna. The JK body is as effective as any vehicle for counterpoise.