Alot of groovy things could be done by using different nac's. P25 Spectra Radios are getting reasonable even on EBAY. building up repeaters and remote bases for P25 signalling has been done with the Maxtrac and Rafius gear. Just validate the NAC on Rx and pass it along. Tx could just just be 9600 baud data stream to tx modulator. Valid NAC could serve as COR