it is sent over audio, but the audio is a modulated bitstream that sounds like your old modem. It is sent over VHF on a radio that the ACARS monitors, you could probably find the local frequencies somewhere and listen to it, but again it would just sound like white noise a modem would generate.How does ATC send a pre departure clearance over the computers instead of over the audio?
Dork.it is sent over audio, but the audio is a modulated bitstream that sounds like your old modem. It is sent over VHF on a radio that the ACARS monitors, you could probably find the local frequencies somewhere and listen to it, but again it would just sound like white noise a modem would generate.
there is a service provider that facilitates the actual communication between the ground equipment and aircraft. On the ground end messages are created in software and sent to the communication service provider along with the aircraft it is intended for, and the service provider dispatches the message and the aircraft ACARS software receives and displays it. On the aircraft the message is created in software (hosted by onboard computers and displayed on the FMS or a dedicated ACARS box) and addressed to the desired recipient (dispatch and possibly others). This is sent back down the communications service provider over the VHF datalink and they send it wherever it needs to go.
you can basically think of it as AIM or something. you type a message, tell it what aircraft it is for and hit "send", and the message goes to a server, which transmits it over VHF and the aircraft displays it. From the aircraft you type a message, tell it where to go and hit "send", it goes over VHF to the server, which sends it back to your messenger. Pretty much just a fancy instant messaging protocol with one side over VHF instead of a network like the internet.
As for how the software might look, at expressjet the dispatchers have a screen with all the aircraft they are following. they just right click an aircraft and pick a menu option and they get a window to type a message and a button to send it. When one comes in it pops up a message box with the message from the aircraft.
PDCs would be similar but originate from ATC instead of a dispatcher with different software.