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HFDL (High Frequency Data Link)

HFDL (high frequency data link) is the generic term for a system in use by long haul airlines for aircraft tracking and text messaging. It operated by the company ARINC as the GLOBALink network - on behalf of aeronautical companies.

Primarily HFDL is used to automatically convey the status and location of an aircraft to ground crews at regular intervals, and is similar to the ACARS system used on VHF frequencies. 

The world-wide HFDL (ARINC GLOBALink) network has 17 nodes (ground stations) covering aviation across the globe and also provides a LDOC (voice network) - allowing for phone patch services, etc.


How to listen 

To intercept HFDL you firstly need to determine the active frequencies in use, once established on the working frequency you pass the received audio through your computers' audio interface into the decoding software (listed below).

This really is easier than it sounds. Essentially you tune your receiver, open the software, then patch the headphone cable of your receiver to the mic or line input of your computer soundcard. The software will then display the text transmitted in the HFDL broadcast.
 
Determining active frequencies:
Each node (or ground station) has a pool of frequencies available to use, and chooses two depending on ionospheric conditions.
To signal to aircraft which frequencies are in use ground stations transmit a status approximately every 30 seconds on the two active frequencies. 

To find the active channels, monitor the frequencies in the pool of listed node frequencies until you hear the ground station data burst (which will occur roughly every 30 seconds).

 
HDFL AUDIO SAMPLE

 

Decoding Software:
There are several programs, both free and paid, available to download which will decode HFDL.
[PC-HFDL v1 - free] [PC-HFDL v2] [CODE300-32] [Krypto500] or [MULTI-PSK].
There is also a yahoo user group available by searching HFDL - providing more info and free software.

You can track the decoded locations of aircraft using the online resource www.radarbox24.com/ or http://flightaware.com/live/  - in addition to this PC-HFDL v2 will display an aircraft location in google earth.

Also available is the VHF ACARS system on 131.550 (or 136.975 at some locations).
Using a scanner and software you can receive the same data from aircraft in your locality.
Software includes [KG-ACARS - free ] [MULTI-PSK] [ACARSD - free]

Asia / Pacific HFDL Frequencies

The pacific node is located in Auckland, New Zealand.
It operates on the following frequencies (KHz USB):

3016, 3404, 5583, 6535, 8873, 8921, 10084 - primary, 11327, 11351, 13351, 17916 - secondary. day, 21949.

The Asia node is in Thailand:

3470, 4687, 5655, 6535, 8825, 10066, 13270, 17928, 21949

LDOC:

3494, 6640, 8933, 11342, 13348, 17925, 21964

 

Information correct as of 20/11/2019