This is the same way as monitoring VHF ACARS. As with VHF ACARS, there are several programs available that will decode it.
PC-HFDL, which can be downloaded at?http://www.chbrain.dircon.co.uk/download/PC-HFDL%202.042%20Setup.zip.
PC-HFDL is a fairly simple and straightforward program to run. Just install it, hook your shortwave receiver to your sound card, and you’re ready to go. Be sure to read the manual file which will help you get started.
HF ACARS is transmitted on several HF frequencies including the following:
All frequencies will be in upper sideband (USB) mode.
Transmissions are in the form of data bursts as on the VHF frequencies, but the bursts will sound different as they are sent at a slower data rate than the VHF ACARS signal. As with VHF ACARS monitoring, the best results are achieved by leaving the HF receiver on one frequency and monitoring for a while. The same type of isolation using a 1:1 audio transformer between the HF receiver and soundcard input is recommended.
Some more Radio Related Information by the author on his website here ? http://www.g4guo.blogspot.com.au/