OK, I just wasn't sure. I work on simulcast systems a good bit (multiple transmitters on a single frequency working in unison for coverage)
That sort of system requires the frequencies to be exact, hence a 5/10Mhz reference for the transmitters. and a 1PPS (pulse per second) signal to the channel banks to control audio launch to be equal and delayed in most cases to account for jitter and network transport delays. All that is spit out of a pretty substantial GPS unit. THe ones Motorola uses actually have two receivers, two internal standards (one of which is rubidium). I am thinking that trying to build a standard might be difficult as the GPS actually bumps the standard peak times into synchronization and the internal reference is actually the corrected source. But for a single repeater that is not exhibiting drift issues, I really don't know that you would gain anything other than bragging rights.