I finally gathered all the parts I needed to install the big antenna on the CUCV.
I'm not really sure what this was used for, but I think it was a training antenna for triggering or jamming IEDs? Not sure. Anyway, there was a 315MHz whip antenna mounted in a plexiglass strip that is screwed into the lid of the antenna tube. Below the antenna is a 40db attenuator (why?) then a long bit of thin coax down the otherwise empty tube to the PL-259 in the base.
I picked up a Comet SBB-5NMO for a couple reasons- it's the tallest that can fit inside the tube, and and it doesn't need a ground plane. I also got a 10" bulkhead connector and an adapter to make it NMO. This was a bit of a mistake. My plan was to screw a nut underneath, and another inside the tube at the base- but that would have prevented the spring from bending.
Instead I have the nuts on each side of the tube base. This will work for now and let the spring move some, but I'll noodle the mount set-up.
Once the antenna was inside the tube, I found another problem; the antenna flexes and will bang around inside the tube- not ideal. Remember that plexiglass piece that's screwed into the tube lid? I put a rubber grommet in the hole (where the whip was mounted) and fed the Comet antenna up through. This keeps the upper part of the antenna centered in the tube and not slapping around.
For giggles I sat the tube on top of the riser- easily gets the whole antenna above the roof-line but between the weight of the antenna assembly and the wind load I expect, I think the bracket will crack over time. I pulled the riser off and bolted the antenna to the bracket and connected the antenna feed line from the radio.
The results are very good. I'm hitting repeaters loud-&-clear I usually can't hit from my driveway. The signal is getting in and out of the tube just fine. The Sheriffs' and fire freqs are coming in better than the previous as well.