CPDLC

[jcherepy]

According to a WiKipedia article CPDLC "...or HF bands for long-distance communication ...".

So, what are the HF frequencies and is there any software out there to decode the transmissions?

Bill

 

[ATCTech]

CPDLC commands are sent via satellite, VHF, then HF, in that (preferred) order depending on what services the aircraft is logged into at the time. They are sent via the same Rockwell Collins ARINC and SITA networks as VDL etc. on VHF and via HFDL frequencies on HF (ARINC only of course, SITA does not operate HF). I'm yet to see any evidence of a decoding package online and CPDLC has been around on HF for many years.

 

[majoco]

PC-HFDL is the almost universally recognised decoder for HFDL and it works very well. You can give it a trial for free but for continuing use you have to buy it - US$35 or so. Works very well, simple to set up, very tolerant of audio levels and it will even plot aircraft positions on google earth automatically!
Google for HFDL to get the frequencies, there's quite a few around the world but each station will only have one or two in use at any one time according to propagation and number of aircraft in its area. Once you get PC-HFDL working it will receive all the frequencies and display them.

 

[jcherepy]

Thanks for the reply. I wondered when it said it used HF when satellite would make more sense for data comms.

Bill

 

[ATCTech]

The original idea was that polar route flights would at times be out of range of both VHF and satellite coverage so HF would be the third level of air interface. I have no statistical data, but I would imagine the global coverage is now at a level where that happens quite infrequently.

Don't forget that ATC (CPDLC) commands must be handled as high priority (time-critical) over routine air/ground traffic so HF is a very undesirable interface for positive IFR control, especially when parallel routes are in use with non-radar separation. The last thing ATC wants is a delayed response to a course change or flight level change instruction while aircraft performance data or ATIS requests are being handled.

 

[majoco]

Don't forget that ATC (CPDLC) commands must be handled as high priority (time-critical) over routine air/ground traffic so HF is a very undesirable interface for positive IFR control, especially when parallel routes are in use with non-radar separation. The last thing ATC wants is a delayed response to a course change or flight level change instruction while aircraft performance data or ATIS requests are being handled.

Well said - and this completely shoots down all those who keep asking "Why don't they use digital comms for VHF ATC".