On this page I will share my insights and experience with the High Frequency Datalink (HFDL) system. I am not by any standard an expert on this subject so please also check what’s out there on the internet, for example on http://udxf.nl/modes.html or in groups like https://acars-vdl2.groups.io/g/HFDL.

Besides an antenna and radio or SDR that is able to receive HF you will also need software to decode HFDL. A popular Windows based program is PC-HFDL and for Linux DumpHFDL is often used. The latter is the program I use with an AirspyHF+ Discovery SDR and a Raspberry Pi4. DumpHFDL is also part of the excellent DragonOS Raspberry Pi OS.

The information below is based on output generated by DumpHFDL.

HFDL message composition

There are several types of messages on HFDL. I only detail the basic information on this page so it is very well possible you see other messages also. But the main information that is visible in decoded HFDL messages is available in the messages below. I have added my remarks in red:

For the reception details HFDL see here.

But you can also see other messages in which the basis composition is the same but in which additional messages or information is included like:

[2022-03-31 06:55:10 GMT] [10081.0 kHz] [3.7 Hz] [-31.9/-38.6 dBFS] [6.7 dB] [600 bps] [D]
Downlink LPDU:
Src AC: 142
Dst GS: Shannon, Ireland
Type: Unnumbered ack’ed data
Enveloped data:
ACARS:
Reassembly: skipped
Reg: RA73100 Flight: SU1443
Mode: 2 Label: 26 Blk id: 7 More: 0 Ack: ! Msg num: M61A
Message:
ETA01AFL1443 /31310419UIIIUUEE
FUEL 116
TEMP- 2
WDIR24023
WSPD 68
LATN 63.852
LONE 82.529
ETA0808
TUR
ALT34000

DumpHFDL script

The sh script I use to activate DumpHFDL on the RPi is as follows:

dumphfdl –soapysdr driver=airspyhf –sample-rate 256000 11184 11306 11312 11318 11321 11348 11354 11384 11387 –output decoded:text:file:path=/home/ubuntu/dumphfdl_files/hfdl_logs/hfdl.log,rotate=daily –utc –prettify-xml –system-table /usr/src/dumphfdl/etc/systable.conf –system-table-save systable-new.conf –bs-db /home/ubuntu/dumphfdl_files/basestation_db/basestation.sqb –ac-details verbose –output decoded:text:udp:address=192.XXX.XXX.130,port=30099

I have similar files for all the HFDL frequency bands. Ofcourse the UDP address should reflect the actual IP address that you want the HFDL data to be sent to. If you don’t use this then delete the complete –output line.

Ground station frequencies

The current system table for HFDL is Version 51 as can also be found in files section of the earlier mentioned groups.io HFDL group. Depending on the bandwidth of your radio or SDR these frequencies can be added to the sh files that activate DumpHFDL. I use an RTL-SDR V3 for HFDL and this means that I can roughly fit frequencies within a MHz in a single file. So I have files for 3, 5, 6, 8 MHz etc. that I use.

System table version 51.

Ground Station ID 1
SAN FRANCISCO – CALIFORNIA
UTC UNLOCKED
Longitude 121 45 33 W Latitude 38 23 4 N
Squitter Version 0
Number of frequencies 8
Frequency 21934000 Hz Master Frame Slot 4
Frequency 17919000 Hz Master Frame Slot 12
Frequency 13276000 Hz Master Frame Slot 8
Frequency 11327000 Hz Master Frame Slot 4
Frequency 10081000 Hz Master Frame Slot 4
Frequency 8927000 Hz Master Frame Slot 12
Frequency 6559000 Hz Master Frame Slot 8
Frequency 5508000 Hz Master Frame Slot 4

Ground Station ID 2
MOLOKAI – HAWAII
UTC UNLOCKED
Longitude 157 11 11 W Latitude 21 11 3 N
Squitter Version 0
Number of frequencies 12
Frequency 21937000 Hz Master Frame Slot 0
Frequency 17919000 Hz Master Frame Slot 7
Frequency 13324000 Hz Master Frame Slot 3
Frequency 13312000 Hz Master Frame Slot 3
Frequency 13276000 Hz Master Frame Slot 3
Frequency 11348000 Hz Master Frame Slot 11
Frequency 11312000 Hz Master Frame Slot 11
Frequency 10027000 Hz Master Frame Slot 11
Frequency 8936000 Hz Master Frame Slot 0
Frequency 8912000 Hz Master Frame Slot 0
Frequency 6565000 Hz Master Frame Slot 7
Frequency 5514000 Hz Master Frame Slot 7

Ground Station ID 3
REYKJAVIK – ICELAND
UTC UNLOCKED
Longitude 22 27 19 W Latitude 63 50 49 N
Squitter Version 0
Number of frequencies 7
Frequency 17985000 Hz Master Frame Slot 11
Frequency 15025000 Hz Master Frame Slot 7
Frequency 11184000 Hz Master Frame Slot 3
Frequency 8977000 Hz Master Frame Slot 0
Frequency 6712000 Hz Master Frame Slot 11
Frequency 5720000 Hz Master Frame Slot 7
Frequency 3900000 Hz Master Frame Slot 3

Ground Station ID 4
RIVERHEAD – NEW YORK
UTC UNLOCKED
Longitude 72 38 14 W Latitude 40 52 54 N
Squitter Version 0
Number of frequencies 7
Frequency 21931000 Hz Master Frame Slot 1
Frequency 17919000 Hz Master Frame Slot 9
Frequency 13276000 Hz Master Frame Slot 5
Frequency 11387000 Hz Master Frame Slot 1
Frequency 8912000 Hz Master Frame Slot 9
Frequency 6661000 Hz Master Frame Slot 5
Frequency 5652000 Hz Master Frame Slot 1

Ground Station ID 5
AUCKLAND – NEW ZEALAND
UTC UNLOCKED
Longitude 174 48 34 E Latitude 37 0 55 S
Squitter Version 0
Number of frequencies 6
Frequency 17916000 Hz Master Frame Slot 12
Frequency 13351000 Hz Master Frame Slot 8
Frequency 10084000 Hz Master Frame Slot 4
Frequency 8921000 Hz Master Frame Slot 12
Frequency 6535000 Hz Master Frame Slot 8
Frequency 5583000 Hz Master Frame Slot 4

Ground Station ID 6
HAT YAI – THAILAND
UTC UNLOCKED
Longitude 100 23 18 E Latitude 6 56 15 N
Squitter Version 0
Number of frequencies 7
Frequency 21949000 Hz Master Frame Slot 10
Frequency 17928000 Hz Master Frame Slot 6
Frequency 13270000 Hz Master Frame Slot 2
Frequency 10066000 Hz Master Frame Slot 10
Frequency 8825000 Hz Master Frame Slot 6
Frequency 6535000 Hz Master Frame Slot 2
Frequency 5655000 Hz Master Frame Slot 10

Ground Station ID 7
SHANNON – IRELAND
UTC UNLOCKED
Longitude 8 55 35 W Latitude 52 44 38 N
Squitter Version 0
Number of frequencies 8
Frequency 11384000 Hz Master Frame Slot 2
Frequency 10081000 Hz Master Frame Slot 2
Frequency 8942000 Hz Master Frame Slot 6
Frequency 8843000 Hz Master Frame Slot 6
Frequency 6532000 Hz Master Frame Slot 10
Frequency 5547000 Hz Master Frame Slot 2
Frequency 3455000 Hz Master Frame Slot 6
Frequency 2998000 Hz Master Frame Slot 6

Ground Station ID 8
JOHANNESBURG – SOUTH AFRICA
UTC UNLOCKED
Longitude 28 12 21 E Latitude 26 7 45 S
Squitter Version 0
Number of frequencies 8
Frequency 21949000 Hz Master Frame Slot 10
Frequency 17922000 Hz Master Frame Slot 6
Frequency 13321000 Hz Master Frame Slot 2
Frequency 11321000 Hz Master Frame Slot 10
Frequency 8834000 Hz Master Frame Slot 6
Frequency 5529000 Hz Master Frame Slot 10
Frequency 4681000 Hz Master Frame Slot 6
Frequency 3016000 Hz Master Frame Slot 6

Ground Station ID 9
BARROW – ALASKA
UTC UNLOCKED
Longitude 156 34 37 W Latitude 71 15 30 N
Squitter Version 0
Number of frequencies 19
Frequency 21937000 Hz Master Frame Slot 10
Frequency 21928000 Hz Master Frame Slot 10
Frequency 17934000 Hz Master Frame Slot 6
Frequency 17919000 Hz Master Frame Slot 6
Frequency 11354000 Hz Master Frame Slot 2
Frequency 10093000 Hz Master Frame Slot 2
Frequency 10027000 Hz Master Frame Slot 2
Frequency 8936000 Hz Master Frame Slot 10
Frequency 8927000 Hz Master Frame Slot 10
Frequency 6646000 Hz Master Frame Slot 6
Frequency 5544000 Hz Master Frame Slot 2
Frequency 5538000 Hz Master Frame Slot 2
Frequency 5529000 Hz Master Frame Slot 2
Frequency 4687000 Hz Master Frame Slot 2
Frequency 4654000 Hz Master Frame Slot 2
Frequency 3497000 Hz Master Frame Slot 10
Frequency 3007000 Hz Master Frame Slot 10
Frequency 2992000 Hz Master Frame Slot 10
Frequency 2944000 Hz Master Frame Slot 10

Ground Station ID 10
MUAN – SOUTH KOREA
UTC UNLOCKED
Longitude 126 14 19 E Latitude 35 1 56 N
Squitter Version 0
Number of frequencies 8
Frequency 21931000 Hz Master Frame Slot 3
Frequency 17958000 Hz Master Frame Slot 11
Frequency 13342000 Hz Master Frame Slot 7
Frequency 10060000 Hz Master Frame Slot 3
Frequency 8939000 Hz Master Frame Slot 11
Frequency 6619000 Hz Master Frame Slot 7
Frequency 5502000 Hz Master Frame Slot 3
Frequency 2941000 Hz Master Frame Slot 7

Ground Station ID 11
ALBROOK – PANAMA
UTC UNLOCKED
Longitude 79 22 25 W Latitude 9 5 4 N
Squitter Version 0
Number of frequencies 6
Frequency 17901000 Hz Master Frame Slot 6
Frequency 13264000 Hz Master Frame Slot 2
Frequency 10063000 Hz Master Frame Slot 10
Frequency 8894000 Hz Master Frame Slot 6
Frequency 6589000 Hz Master Frame Slot 2
Frequency 5589000 Hz Master Frame Slot 10

Ground Station ID 13
SANTA CRUZ – BOLIVIA
UTC UNLOCKED
Longitude 63 9 24 W Latitude 17 40 15 S
Squitter Version 0
Number of frequencies 7
Frequency 21997000 Hz Master Frame Slot 3
Frequency 17916000 Hz Master Frame Slot 11
Frequency 13315000 Hz Master Frame Slot 7
Frequency 11318000 Hz Master Frame Slot 3
Frequency 8957000 Hz Master Frame Slot 11
Frequency 6628000 Hz Master Frame Slot 7
Frequency 4660000 Hz Master Frame Slot 3

Ground Station ID 14
KRASNOYARSK – RUSSIA
UTC UNLOCKED
Longitude 92 35 0 E Latitude 56 9 9 N
Squitter Version 0
Number of frequencies 7
Frequency 21990000 Hz Master Frame Slot 4
Frequency 17912000 Hz Master Frame Slot 12
Frequency 13321000 Hz Master Frame Slot 8
Frequency 10087000 Hz Master Frame Slot 4
Frequency 8886000 Hz Master Frame Slot 12
Frequency 6596000 Hz Master Frame Slot 8
Frequency 5622000 Hz Master Frame Slot 4

Ground Station ID 15
AL MUHARRAQ – BAHRAIN
UTC UNLOCKED
Longitude 50 38 23 E Latitude 26 16 25 N
Squitter Version 0
Number of frequencies 6
Frequency 21982000 Hz Master Frame Slot 1
Frequency 17967000 Hz Master Frame Slot 9
Frequency 13354000 Hz Master Frame Slot 5
Frequency 10075000 Hz Master Frame Slot 1
Frequency 8885000 Hz Master Frame Slot 9
Frequency 5544000 Hz Master Frame Slot 5

Ground Station ID 16
AGANA – GUAM
UTC UNLOCKED
Longitude 144 49 41 E Latitude 13 29 19 N
Squitter Version 0
Number of frequencies 7
Frequency 21928000 Hz Master Frame Slot 1
Frequency 17919000 Hz Master Frame Slot 9
Frequency 13312000 Hz Master Frame Slot 5
Frequency 11306000 Hz Master Frame Slot 1
Frequency 8927000 Hz Master Frame Slot 5
Frequency 6652000 Hz Master Frame Slot 1
Frequency 5451000 Hz Master Frame Slot 9

Ground Station ID 17
CANARIAS – SPAIN
UTC UNLOCKED
Longitude 15 24 18 W Latitude 27 57 39 N
Squitter Version 0
Number of frequencies 6
Frequency 21955000 Hz Master Frame Slot 4
Frequency 17928000 Hz Master Frame Slot 12
Frequency 13303000 Hz Master Frame Slot 8
Frequency 11348000 Hz Master Frame Slot 4
Frequency 8948000 Hz Master Frame Slot 12
Frequency 6529000 Hz Master Frame Slot 8