The 5/8th wave or 1/2 wave verticals obtain their gain because the current area in the antenna is elevated higher above the groundplance. Without a flat groundplane extending out some distance a 5/8th wave has no gain, it can even have loss.
Put a 5/8th wave low on a vehicle so only the upper part clears the sheet metal, and pretty much every advantage goes away. You might as well just use a 1/4 wave on the roof as a 5/8th on a fender.
Thanks for your thoughts, everyone-
I think I may have to check into the performance of my 1/4 wave some more, and consider the dual-1/4 wave, even if it's not truly omnidirectional.
W8JI has given me the background for what I'd thought true all along -- that fender mounting my 5/8 wave would have some drawbacks - I see two of them mentioned here:
- off-center groundplane, which I don't have right now with the center of a 4' x 5' metal roof as a groundplane. I might have a problem with groundplane once I moved to the extreme side of the vehicle right against the fender.
- radiation point would definitely be at the same height as the 1/4 wave, or maybe even slightly lower.
Paul is correct that it may work as well as the 1/4 wave at the roof height for that reason.
So that solution would solve my height problem, but would possibly leave me with the reduced repeater quality-of-signal that I get with the 1/4 wave.
Should not be hard to try and find out, though.
Turns out I don't have stake holes in the truck! I thought there were some down underneath the bedliner, but there aren't in the Frontier.
I can mount something back there though, as a test.
Just makes life challenging when I'm trying to carry a load of lumber or plywood - one more thing to worry about the load damaging..