Originally Posted by InlandAZ
Does anyone have a current list of DPS frequencies for Arizona? Predominantly interested in the Phoenix area, plus air frequencies. I'm in Chandler if that helps...
Also is it safe to assume that their air frequencies are AM? (And if anyone cares to explain just why most air freqs utilize AM - I'd be interested in reading it).
Aero frequencies are in the AM mode for interference reasons. When two stations transmit using AM they can both be heard at the same time to receiving stations (IE. other aircraft/ATC) This wouldn't be the case with FM which takes up quite a bit of the band. When someone transmits with FM it would basically cover the entire frequency and no one else would be heard. So for safety reasons they use the AM mode in case someone keys up on top of another transmitting station.
An example: You have N56JLK at Airport 1 on 122.800 unicom and 35 miles N9846L at Airport 2 on 122.800 unicom. Both aircraft are 35 miles away from eachother but at an altitude of 1000 feet if they're both reporting maneuvers or intentions at the same time, to other pilots they would block eachother out if the radios transmitted using FM. With AM you'll still hear both aircraft's transmissions. There will be a whine but you'll still be able to make it out.