[LandCruisers4Life]

Here's an interesting piece of information from the Larsen site. I have been looking at Comet and Diamond antennas too.

Ground plane availability is another critical factor in mobile antenna performance and must be considered when
determining the location and type of the antenna. Ground plane requirements vary given the type of mobile
antenna and the frequency of operation. A typical 5/8 wave antenna at 150 MHz requires a ground plane at least
42” in diameter. At 450 MHz 15” is required, and at 800 MHz a minimum of 8” is considered sufficient.
In terms of mounting mobile antennas on a vehicle, there are five general locations: roof, front fender, rear fender,
trunk and rear window glass (although other glass mount locations may be used). Of these, the center of an
automobile roof is considered the best for mobile antenna placement, followed by the center of the trunk lid, the
fenders, then on-glass mounting. This ranking is determined by the amount of ground plane provided by the
positioning and clearance from obstruction (i.e., the roof line). The center of the roof is considered the ideal
mounting location, provided the roof is metal. The diagram below illustrates the effective loss (at 800 MHz) due to
insufficient symmetrical ground plane.