On Saturday, February 15, 2014 9:58:10 PM UTC-6, Jeff Liebermann wrote:
However, a J-pole (or Zepp) is not a 1/2 wave antenna. The driven
element is a 1/4 wavelength long, and therefore DOES require a ground
plane.

Sorry, that is not correct. Both a Zepp and a J-pole are 1/2WL antennas fed with a 1/4WL matching section of transmission line containing mostly balanced transmission line currents. Here is a plot of the two currents in the matching section. The difference in those two currents is the common-mode current which indeed does radiate. The point is that the average differential transmission line current is more than 10 times the average common-mode radiating current so the matching section is acting primarily as a transmission line, transferring RF energy to the primary radiating element which is indeed 1/2WL element.

http://w5dxp.com/ZeppCrnt.jpg

Does the matching section radiate? Of course it does. But because the common-mode current is a small percentage of the total current, it does not radiate much and transfers most of the RF energy to the 1/2WL radiating element.. And yes, that small percentage of common-mode current on the matching section indicates that it is also acting as the antenna counterpoise in the above graph. But most of the radiation from the antenna is from the center of the 1/2WL element, just as it is for a 1/2WL dipole. In fact, a Zepp meets the IEEE definition of a dipole because it contains two electrical poles.
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73, Cecil, w5dxp.com