Roof mount vs rear bar on pickup?

[mr.syntrx]

I've just bought a 2009 Holden Colorado crew cab pickup, and at the moment I'm planning a VHF and UHF install. The tub has a bar that runs up behind the cab at roof level, that I'm considering mounting my antennas on.

I plan to go with "no ground" antennas (end fend half wave or similar), with one on each side of the truck, mounted to this bar using angle brackets. Is there going to be a huge performance difference in mounting antennas up on this bar, this compared with popping holes in the roof?



I'm thinking of going for a Larsen NMOWB150B on VHF, and a Maxrad BMWU4002S on UHF.

I need a VHF antenna for 2m ham, and a land mobile system with a 157MHz input/162MHz output.

UHF is more challenging, as I need to cover from 411MHz to 477MHz, including the 70cm amateur band. I may end up doing this with two radios, but at least initially I'll be a using a UHF low split XTS5000 in an XTVA. In future, I might install an additional radio just for 477MHz, but seeing as I very rarely use those frequencies I'd prefer not to at this stage.

[motorola_otaku]

Bond the bar to the tub with ground braid, and then from the tub to the frame just to be on the safe side. You shouldn't have any problem using normal ground-plane-required antennas, but having a good RF ground to the bar is key.

Honestly I'd just go with quarter-wave spikes unless you have a pressing need for gain, cut to the center of your required transmit range. I like these.

[mr.syntrx]

The factory grounding seems pretty decent at the moment but I was planning on beefing it up to be sure anyway.

I'm in rather hilly terrain so gain isn't too much of a requirement, I figured I'd just keep a 5/8-wave around for VHF for when I'm out on the road (on flatter ground) and only need access to the ham band.