My first question is, to what purpose? You didn't post an amateur call, so I don't know if this is for amateur use, if it's for pirate/unlicensed/illegal use, for commercial use, or what.
Putting up a proper repeater is no small undertaking, nor is it cheap. If you are looking at a commercial site, you need a proper duplexer to protect yourself, and others, from interferance, as well as high quality coax (heliax) and other concerns.
If this is an amateur repeater, then you need an expensive duplexer--because none of the cheaper "notch" duplexers you see on eBay will work for the close offset needed for amateur work.
None of these radio interface cables, that I'm aware of, offer ANY sort of "id'er" "time out timer" any sort of controls or protection for the radio.
You MUST be under control of your repeater. If it "locks up" on transmit, due to some failure, interferance, or intentional jamming, you MUST have a control method to shut it down ----3 minutes in US amateur practice.
That means anyway you can "git er done."
You can stay withing 3 minutes physical time of the repeater whenever it is powered up and receiving.
You can control it through a phone line and probably the internet if you can make it reliable.
You can use a (in amateur service) 222mhz or higher link
In addition to all that blather, some mobiles make very poor repeaters--they were never designed for extended transmit conditions, and some have poor front end rejection qualities so far as interferance goes.
There is a reason why "real" commercial repeaters are so expensive.
One excellant place to do some reading is the "repeater builder" site. There is a LOT of buried information there, including hardware, antennas, and duplexers.
http://www.repeater-builder.com/rbtip/(If you haven't spend at least two hours browsing that site, you haven't been there long enough.)
