Hey U- Op
I just read your question (a tad late) - by now you have no doubt mounted something on your Jeep ?
If not, here is my two cents- if you have done so...?... Oh well--
I have a Jeep Wrangler Unlimited with the fiberglass roof. That roof, right there, presents a challenge to any antenna- and I am making the assumption you have a similar situation;
ie: a Wrangler with the hard fiberglass top
Ah ! what was a girl to do ?
I will get to that in a moment, but first, let me deviate this discussion a few degrees.
You received some good information (excepting that weird advice about cutting off the ball on a whip-- No, don't do that -- "Kid, you'll just put your eye out" *. )
I am going to address the practical side of this antenna issue- at least from my perspective.
I don't know where you off-road, but where I do it can vary between open the Upper Sonoran Desert to the Alpine Tundra. In between is a lot of Limber, Lodgepole pine lined goat tracks that pass for roads (the Central Rockies of Colorado) - those trees alone- they love to snatch away any antennas.
Long, long ago the mountains taught this Cowgirl that except for Motorola low band whips, with their awesomely serious stainless steel springs/ball mounts- nothing was going to survive in my "hills"-- excepting the humble 18" NMO mount'd vertical (also a Motorola design.)
Okay, enuff background colour-
On my Wrangler I drilled a 3/4" hole thru the the fiberglass roof (Horror!.. but, heck- its MY jeep)- and I mounted a NMO connector. Yes, it needs a ground plane- and in my case I used a sheet of copper PC board cemented to the underside of the roof- the NMO connector passes thru it- the coax is soldered to both the connector and to the board (~ 7 by 20 ? ").
How well does it work?.... Its approximately a quarterwave between 140 to 160-something MHz's, with an SWR of <2:1. Its 3/4 wave (and resonant) on ~420-470, with a likewise SWR. Nothing's perfect, but it has survived many a Jeep trail that a flatlander's antenna would have been destroyed. SWR and radiation patterns start to become minor deals.
Have I been concerned that this is not the ultimate antenna, radiation pattern, SWR etc. wise ?...
........simple answer--- No. This antenna is still on my vehicle when many others would have long ago been in some ditch.)
U-Op, you are and off road'er- you know sturdy beats cutesy every time.
Lauri
_________________________________________________________
.
* Sorry, and with an apology to one of my TV favorite Christmas movies-
"A Christmas Story"
.
.
.