HIGH FREQUENCY DATA LINK
Section
created on 04 March 2002
For PC-HFDL logs try HF-ACARS mailing list. Please try to fill the DATABASE on mailing list relevant section with ICAO IDs of missing aircraft loggings
Please send your suggestions for a better website and mailing list. |
And the PC-HFDL decoder using soundcard is almost completed by Charles H. Brain
This document describes how to use PC-HFDL
PC-HFDL is a Windows based decoder for the ARINC 635-3 HF data-link protocol. To receive these transmissions
a good quality USB HF receiver is required; preferably one that can support a bandwidth of 2.8 Khz.
Simply copy the executable to a suitable directory. The sound level is controlled through the usual Windows Mixer controls. The modem software includes digital AGC so it should be fairly tolerant of level. However do not overdrive your soundcard.
The program does a lot of digital signal processing so a fast machine is required. The slowest machine that the software has been tested on is a 500Mhz PIII. However it may run on slower machines. Please let me know if it does. It will also not be compatible with older sound cards.
You can cut and paste from the main display window.
Double click on an Aircraft and further information is displayed. In the text box at the top. This includes where available, the time last heard, the ICAO 24 bit address, the flight ID and last position. A position of 180/180 means that the aircraft does not have its position available.
The currently known (there are more) frequencies are
Information was supplied by Day Watson
ARINC 635-3 aka HFDL aka GlobeLink/HF is based on a number of interconnected ground stations. Each ground station transmits a frame called a Squitter every 32 seconds. The Squitter frame informs aircraft of the system status, provides a timing reference and provides protocol control. Each ground station has a time offset for its Squitters. This allows aircraft when trying to log on to jump between ground stations finding the best one as fast as possible. When passing traffic Time Division Multiplexing (TDMA) is used. This prevents two aircraft transmitting at the same time causing collisions.
Let us pretend we are an aircraft. We have taken off and want to logon to the system.
Firstly we look at all the ground stations local to us, i.e within 3000 miles.We compare signal strengths, look at multi-path and see how busy each one is.
Once we have decided which ground station we want to use, we listen to that ground station to see what slots are to be used for random access. We decide on a slot and then send a log-on message including our ICAO 24 bit aircraft address using the log-on address 0xFF.
If it hears us the ground station sends a logon confirm. The message is sent using the same log-on address of 0xFF and we can tell it is for us as it also contains our unique ICAO 24 bit address. In this message is also the air address that will be used when the ground station is talking to us.
When we then wish to pass traffic we simply request a timeslot to use and then send the message using our air address ( allocated to us by the ground station).
Traffic can either be sent in a single timeslot or a double timeslot, hence the two interleaver settings ( 1.8 sec or 4.2 sec ).
The whole system works in pretty much the same way that GSM mobile phones work except the data rates are slower as it is on HF and there is no speech! The principle is otherwise the same. I have left out a lot of the fine detail but that is up to you to discover!
How does this modem work?
The modem uses a technique called Decision Feedback Equalisation. The received signal after being corrected for frequency error is processed by a digital filter. The digital filter tries to undo the effects of the ionosphere. To do this it uses the preamble and training information in the waveform as a sort of sanity check to see whether its model is correct. When it is not receiving either the preamble or the training information it uses the received data itself. It tries to work out what was sent then feeds that back into its model of the ionosphere, hence the term Decision Feedback. If it gets it wrong then things start to go horribly wrong, garbage in garbage out as they say!
Forward error correction is done using convolutional encoding, the modem using the Viterbi algorithm to correct errors, using the traceback method.
Best of Luck Charles
First HFDL logs by Dani Glikmanas
Dear
Friends,
These are the UPS'logs that I'm receiving now on HFDL. This
flight airborne from SBKP (Campinas) to SAEZ (Ezeiza).
NR AIR CALLS 1
AIR CALL 0 = 31
LPDUS = 1
Max Bit rate 1200 bps
[LPDU UNNUMBERED DATA]
[HFNPDU ACARS GND STN]
2.N309UP1_ N Cl
Nr LPDUs = 1 Ground station ID SANTA CRUZ - BOLIVIA SP ID 0 NOT
SYNCHED
Aircraft ID 31
Slots Requested medium = 0 Low = 0
Max Bit rate 1800 bps U(R) = 4 UR(R)vect = 0
[LPDU UNNUMBERED DATA]
[HFNPDU PERFORMANCE]
20:36:58 UTC Flight ID = UP6198 LAT 23 0 10 S LON 47 8 41 W
Slots Requested medium = 0 Low = 0
Max Bit rate 1800 bps U(R) = 4 UR(R)vect = 0
[LPDU UNNUMBERED ACKED DATA]
[HFNPDU ACARS AID UP6198]
2.N309UP 3B2 M15AUP6198032039 03VCP 2030203020392306EZE _
[LPDU UNNUMBERED DATA]
[HFNPDU PERFORMANCE]
20:40:28 UTC Flight ID = UP6198 LAT 23 0 56 S LON 47 7 21 W
Nr LPDUs = 2 Ground station ID SANTA CRUZ - BOLIVIA SP ID 0 NOT
SYNCHED
Aircraft ID 31
Slots Requested medium = 0 Low = 0
Max Bit rate 1800 bps U(R) = 4 UR(R)vect = 0
[LPDU UNNUMBERED ACKED DATA]
[HFNPDU ACARS AID UP6198]
2.N309UP 3B2 M15AUP6198032039 03VCP 2030203020392306EZE _
[LPDU UNNUMBERED DATA]
[HFNPDU PERFORMANCE]
20:40:28 UTC Flight ID = UP6198 LAT 23 0 56 S LON 47 7 21 W
Nr LPDUs = 2 Ground station ID SANTA CRUZ - BOLIVIA SP ID 0 NOT
SYNCHED
Aircraft ID 31
Slots Requested medium = 0 Low = 0
Max Bit rate 1800 bps U(R) = 4 UR(R)vect = 0
[LPDU UNNUMBERED ACKED DATA]
[HFNPDU ACARS AID UP6198]
2.N309UP 476 M16AUP6198032043 03VCP EZE DOFF 9
[LPDU UNNUMBERED DATA]
[HFNPDU PERFORMANCE]
20:44:34 UTC Flight ID = UP6198 LAT 23 16 47 S LON 47 13 15 W
Nr LPDUs = 1 Ground station ID SANTA CRUZ - BOLIVIA SP ID 0 NOT
SYNCHED
Aircraft ID 31
Slots Requested medium = 0 Low = 2
Max Bit rate 1800 bps U(R) = 4 UR(R)vect = 0
[LPDU UNNUMBERED DATA]
[HFNPDU PERFORMANCE]
20:45:16 UTC Flight ID = UP6198 LAT 23 19 31 S LON 47 15 10 W
Nr LPDUs = 2 Ground station ID SANTA CRUZ - BOLIVIA SP ID 0 NOT
SYNCHED
Aircraft ID 31
Slots Requested medium = 0 Low = 0
Max Bit rate 1800 bps U(R) = 4 UR(R)vect = 0
[LPDU UNNUMBERED ACKED DATA]
[HFNPDU ACARS AID UP6198]
2.N309UP H17 D04AUP6198#DFBA3M1032041VCP EZE
0432P201024005G00090453P201027005G0
0090480P19503
8004G00090513P190016004G00090541P188358003G00090564P182023002G000
9058 1P178053002G00090590P177072004G0009/ ^
[LPDU UNNUMBERED DATA]
[HFNPDU PERFORMANCE]
20:46:02 UTC Flight ID = UP6198 LAT 23 22 31 S LON 47 17 15 W
Ground station ID SANTA CRUZ - BOLIVIA SP ID 0 SYNCHED
NR AIR CALLS 1
AIR CALL 0 = 31
LPDUS = 1
Max Bit rate 1200 bps
[LPDU UNNUMBERED DATA]
[HFNPDU ACARS GND STN]
2.N309UP7_ T v3
The hfdl program decoder is working very well, near 95% of total.
I received messages from American Transair and China Airliners,
4000 nm far from my radio station.
Danis equipment is a Kenwood R5000
and Sony 2001. Receiving messages on 13315 Khz, Santa Cruz de La
Sierra, in Bolivia, 1200 km far from my radio station.
The only PC-HFDL monitoring station 24H daily located in Greece, tracking Bahrain Link on 21.982/17967 (daylight) and 10075/8885 (night)
