hmm - apols if I've guessed wrong, but sounds like you haven't yet RTFM - based both on this question and the questions about the repeater.

Have a look at 

http://op25.osmocom.org/wiki/wiki/HardwarePage

http://op25.osmocom.org/wiki/wiki/RepeaterPage

http://op25.osmocom.org/wiki/wiki/SignalScopePage

- in particular the Hardware page has a method for setting the deviation - or you could spend $ on a store-bought FMD meter : )

73 de KA1RBI