Channels are .030 MHz apart. Many of these channels may now be used for paging, specifically 152.78, which is a nationwide page. Ground stations repeat the airborne half of the converstion, and transmit a continuous tone when idle. From one to three channels are assigned in a particular area.
Service is used on private aircraft.
Channels are spaced 6 kHz apart. A specific block of 29 channels is assigned to each geographical area. Ground frequencies are 45 MHz lower and do not echo the airborne half of the conversation. Service is used on passenger airlines. Each TV channel is 6 MHz wide.