HFDL System Table Update Pattern Emerges

Thanks to Ken on the HFDL mailing list for this intelligence:

2011/10/11(TUE) --> Pacific
DB36(024h): GS ID 1 SAN FRANCISCO(DIXON)
DB37(025h): GS ID 2 MOLOKAI
DB38(026h): GS ID 5 AUCKLAND
DB39(027h): GS ID16 AGANA

2011/10/18(TUE) --> North Atlantic(southern)
DB40(028h): GS ID 4 RIVERHEAD
DB41(029h): GS ID17 CANARIAS(GRAN CANARIA)

2011/10/25(TUE) --> South America
DB42(02Ah): GS ID11 ALBROOK(PANAMA-CITY)
DB43(02Bh): GS ID13 SANTA CRUZ

2011/11/01(TUE) --> Asia, Africa
DB44(02Ch): GS ID 6 HAT YAI
DB45(02Dh): GS ID 8 JOHANNESBURG <-- no change
DB46(02Eh): GS ID14 KRASNOYARSK
DB47(02Fh): GS ID15 AL MUHARRAQ


The next changes may be: (only my personal speculation!!!)

2011/11/08(TUE) --> North Atlantic(northern), Arctic
DB48(030h): GS ID 3 REYKJAVIK
DB49(031h): GS ID 7 SHANNON
DB50(032h): GS ID 9 BARROW

I hope the next would be the last.

You too, huh?

HFDL System Table Now at #47!

Yes, that's right.  Before I was able to post the new PCHFDL.DAT file for ARINC HFDL System Table #43, they put out another one... and another one... and another one... (total is five in about a week).

Obviously, there has not been an opportunity to catch up, and so the file will not be uploaded until this settles down.  Meanwhile, leave PC-HFDL going on a strong ground station all day, until it sends the table out to somebody.  The program will then update itself, and frequencies will replace the numbers.

Also, the changes in all five tables have been very minor.  One can still use old lists and spreadsheets to look up freqs manually.  A hassle, yes, but it works.  Keep in mind that freqs are numbered from the highest down.  Yes, that's right.  San Francisco is using 21943 (F-1) right now.  Gotta love solar peaks.

HFDL System Table #43 / 0x002B Is Now Current!

After a long interval with no changes, Aeronautical Radio, Inc (ARINC) has revised the system table used in its High-Frequency Data Link (HFDL) network.

Two updates, numbers 42 and 43, were issued in the space of about one day.  Number 43 (2B in hex) is still current at this time.

The system table is a lookup database of all frequencies used by HFDL stations.  For our use, it is essential in order to change the numbers passed in HFDL "squitters" to the frequencies in use at a given time.  One can look this up manually on a text file or spreadsheet of the system table, but it is far quicker to configure software to do it automatically.

In the case of the most popular program, PC-HFDL, this can be done in two ways.  The first is to get lucky, and have PC-HFDL open when the system passes the new frequencies to aircraft.  This works for the first few days after a change, before the information finally propagates to all users.

The second, and most practical, procedure is to replace the old pchfdl.dat file in the program's runtime directory.  This is done by obtaining the new file from someone who has made the update, usually from web sites or links posted to mailing lists.  Then close PC-HFDL if it's open.  Find the right directory, rename the existing file to oldpchfdl.dat, and copy in the new one as pchfdl.dat.  Then restart PC-HFDL and see if the numbers have changed back to freqs.

The structure of pchfdl.dat is completely bizarre, containing incomprehensible snippets of HFDL decodes.  However, it works - most of the time.

The new file will be added to this column's web site as soon as I can obtain and test it.  This will probably happen around Thursday.  Tomorrow, I'll be on an airplane myself.

Northwest/ Delta Oddity Continues On Air

The merger between Northwest and Delta Airlines was completed on January 31, 2010. Delta is the surviving company.

A few days ago, the folding of Northwest's booking system into Delta's was completed.The Northwest web site now goes to Delta's. All NW and NWA flight codes should now be DL and DAL.

What's interesting is that NWxxxx and NWAxxx flight numbers are still appearing on ACARS and HFDL. According to several people familiar with such things, this might be due to people manually entering codes that they are used to. Since ARINC, which operates both systems, tracks flights by registration number, this should not cause problems.

Something similar is happening with Mode-S identifiers.

Northwest's aircraft are being repainted into Delta livery. Most should be done by now. I'm less sure of what will happen to the old registrations ending in NW.

New Pchfdl.dat Is Up

A new version of pchfdl.dat, the ARINC system table #35 (0x0023) file for PC-HFDL, has been tested here and found to work properly. It came from the files section of the HFDL mailing list. I've also made it available here at this column's web site.

Close PC-HFDL if you have it open, go to the configs folder of the program's home directory, and rename the old file to something like oldpchfdl.dat . Download this new file as a binary and place it in the configs folder. Restart PC-HFDL. If the system table shows as #35, you're there.

The pchfdl.txt file that supplies the names of the ground stations to PC-HFDL has also been tweaked a bit to finally reflect the name change to PANAMA. It, too, is available on the web site, and should be added to the configs folder in the same manner described above.

HFDL System Table #35 Now Current

Actually, it changed last Thursday. Some lucky individuals have probably gotten it off the air. For the rest of us, PCHFDL.DAT is in the files sections of the UDXF and HFDL mailing lists. Also, I'll post it to the column's web site as soon as I get it and check that it works.

It appears that the only changes are for the Panama station:

13264000 Hz Master Frame Slot 2
8894000 Hz Master Frame Slot 6

More on HFDL

1. James Gilbert in Florida reports that he has the new PC-HFDL version 2.042 working fine under Vista and on a Winradio virtual sound card. Others report similar success with the program and Vista.

2. The new Panama HFDL station is being copied widely working aircraft on 10063 and 17901 kHz. It fills a gap in Central America. James has it in FL on 17 MHz, and so do I in CA. Along with squitters, I have recently logged new aircraft N317UP, N446UP (both UPS), LX-RCV (Cargolux), N17122, N33132 (both Continental), HP-1521, HP-1534CMP (both Copa), and XA-MXQ (Mexicana).

More On New HFDL System Table #34 (0x0022)

Users of PC-HFDL probably know that when ARINC changes the System Table of frequencies used for this huge system, the mismatch is picked up by the program. You see this when it reverts to using numbers instead of frequencies in kHz. Checking the "System Table" box to open the window won't help, because the program still doesn't have the new information.

PC-HFDL does have the ability to update itself, but you have to be lucky. What happens is that the mismatch is also picked up by the "real" HFDL system, which sends aircraft the new table until everyone has it. Those who are listening at the right time, or the real hard core fans who run PC-HFDL 24/7 are already in business.

Everyone else has to update it by hand. Here's what you do:

1. Find the directory containing PC-HFDL. There should be a subfolder called configs (all lower case). This contains, at a minimum, three files auto-generated by PC-HFDL the first time it runs. These are:

pchfdl.ini (don't worry about this one);

pchfdl.dat (contains a lot of weird text and binary stuff that is apparently a capture of the system table from the air; this is how the program updates itself);

pchfdl.txt (a list of ground stations, with unused slots and 0 padded with UNKNOWN).

2. Ordinarily, only pchfdl.dat would need to be changed. However, this time there's a new ground station. This one replaces the long-gone Annapolis station in slot number 11. It's at or near the old Albrook Air Base near Panama City, which was once used by the US until the canal was given back. Therefore the HFDL community has decided to call it ALBROOK in PC-HFDL.

Therefore, two files must be changed.

3. Back up pchfdl.dat and pchfdl.txt somewhere else, so you have untouched copies if you need to revert.

4. Make sure PC-HFDL is not running, or none of the subsequent steps will work.

5. Download the new pchfdl.dat from somewhere. I got my copy from the excellent HFDL group on Yahoo. This is a great group populated by the real heavy duty HFDL monitors, and it is highly recommended. If you don't want to join, a copy of the file is on the Utility World site. It's the same one in use here, though for various reasons I can't guarantee it will be right for everyone.

6. Go to the PC-HFDL config folder and rename the existing pchfdl.dat. Copy in the new one. Make sure the file doesn't get changed in any way, for it indeed IS a binary and must be treated as such. Most problems in this step come from the file getting changed somehow.

7. Now it's time to fix the ground station list. This is easy. Rename pchfdl.txt and open it an any plain text editor like Notepad. Don't use a formatting editor like MS-WORD that adds stuff, unless you know how to save straight text from the program. Find the line containing ANNAPOLIS - MARYLAND and change it to ALBROOK - PANAMA.

When you're done, the text in the file should look like this:

UNKNOWN
SAN FRANCISCO - CALIFORNIA
MOLOKAI - HAWAII
REYKJAVIK - ICELAND
RIVERHEAD - NEW YORK
AUCKLAND - NEW ZEALAND
HAT YAI - THAILAND
SHANNON - IRELAND
JOHANNESBURG - SOUTH AFRICA
BARROW - ALASKA
UNKNOWN
ALBROOK - PANAMA
ANCHORAGE - ALASKA
SANTA CRUZ - BOLIVIA
KRASNOYARSK - RUSSIA
AL MUHARRAQ - BAHRAIN
AGANA - GUAM
CANARIAS - SPAIN

Save as pchfdl.txt and exit.

8. Fire up PC-HFDL, find some squitters to decode, and you should be back in business.

I have working copies of pchfdl.dat and pchfdl.txt for public download on the Utility World web site. You're welcome to them, though of course I must again note that they have no guarantees due to the jungle that is Windows. They were good files whey I put them up there, but that's where my knowledge of them stops.

I also have version34.txt, which is just a straight capture of the contents of the window that comes up when you check the System Table box. It's a good way to get the new table in its entirety. However, it's not needed for the operation of PC-HFDL.

Have a good flight!

New HFDL System Table 34 (0x22) Is Out

Never fails... you disappear for a few days to eliminate a backlog of projects, and all hell breaks loose.

This time it's a new system table for ARINC's global HFDL system. It has apparently added an altogether new ground station in the open slot 11, and changed quite a few things. More when I get it up and running here.

No New HFDL Ground Station

I'm receiving New York squitters now, but there is no mention of a new ground station, and others report that it is no longer being sent. Perhaps confusion in the HFDL system, now resolved?

New HFDL Ground Station?

Nothing from ARINC, but several HFDL ground stations are mentioning a new ground station called UNKNOWN in their squitters. Unfortunately, the closest one to The Land That Short Wave Forgot is New York, and there's not propagation from there yet. We'll try to get some more information.

Digital Mode of the Week: HFDL

HFDL stands for High-Frequency Data Link. It is the HF band portion of a comprehensive, global, air-ground, communications system that also uses VHF and satellite. The ACARS ( Aircraft Communications Addressing and Reporting System) is another part of all this. Most people associate ACARS with VHF, but the HFDL protocol can carry it as well.

The HFDL standard is ARINC Report 635-3 (HF Data Link Protocols), which can be ordered from the company, Aeronautical Radio Inc, for a price. ARINC is a private company, formerly owned by the airlines, but now contracting with them for communication services.

Like packet radio, HFDL has layers. These are physical, link, and subnetwork. The subnetwork layer isn't important for receiving, since we're just randomly decoding everything on a frequency.

The physical layer is, once again, the actual transmission of data over the radio. HFDL is a single-tone, phase-shift keyed, text-based, error-checking mode with a baseband audio carrier frequency of 1440 Hz. It is tuned in USB, and the 1440 Hz center is critical for decoding. LSB works too, but the dial frequencies won't match the ones in the ARINC database.

Each burst begins with the unmodulated 1440-Hz tone, so that the decoder's automatic frequency control can lock on. This is the scary-sounding "frequency error" that is output by the decoder. Errors within 50 Hz or so can be ignored. This beeping, followed by hiss, is what the mode sounds like.

The symbol speed is fixed at 1800 baud, but the data rate is determined by the exact modulation used. BPSK is 300 bps, QPSK is 600, and 8PSK is 1200 or 1800. 300 is by far the most common, though I've heard it go up to 1200. Tuning error, modulation type, and signal quality are best viewed on a phase constellation display like the one in the PC-HFDL program.

Frequencies are stored in a numbered database, called a system table, which is sent by ARINC to all stations. A few times a year, the table is replaced by a new one with a higher number. The resulting mismatch causes aircraft software to request an update, which we receive too. At least one decoding program (again PC-HFDL) will grab these for its own use, if you're lucky to hear one. Afterward, the frequencies show up in kHz, which is extremely convenient. Otherwise, there are ways to update PC-HFDL manually with system tables found online.

Old databases aren't useless. The frequencies always come from the same pool, and never change that much.

Ground stations pick 2-3 frequencies from the table depending on propagation. This may change every few hours. The frequencies being used by the entire network are sent, two stations at a time, in the "squitter." (Squitter in air comm jargon is an unsolicited information transmission. More on these soon.)

Aircraft can choose frequencies, or even ground stations. If reception exists, they can also switch to satellite or VHF. The comm status is passed to the ground station. All this is automatic, so the crew can just get on with flying the airplane.

Transmission types are uplinks (ground-air), downlinks (air-ground), and the aforementioned squitters. A squitter is always sent every 32 seconds by the ground. It contains various network maintenance data, including all the frequencies (if you wait long enough). It's also a quick propagation check, because you're never more than half a minute from a ground transmission coming from a known location. Of course, aircraft may be heard even if the squitters are inaudible, and vice versa.

HFDL uses a simple form of time-division multiplex. The entire 32-second cycle is divided into 13 numbered slots of 2.5 seconds each. Slot 0 is always the squitter, leaving 1-12 for up- and downlinks. Databursts always occupy all of one slot, though the various overheads of the physical layer reduce the actual transmission of data to 1.8 seconds. Sometimes an uplink with an embedded ACARS message might require a double-length transmission using two slots.

The network assigns the use of these slots, keeping stations from transmitting at once. Assignments are made by ID, a temporary hexadecimal number given each aircraft at logon.

The use of condensed message formats and lookup tables makes HFDL extremely efficient in its use of air time. It's amazing how much can be crammed into a 2-second burst. Most decoders have a "verbose" mode which will output everything. Hundreds of lines with every kind of count and measurement you can think of will scroll madly up your screen, filling your buffer at a merry rate.

Really long ACARS messages, like airport arrival information (ATIS), can be sent in numbered packets (same as on VHF). Otherwise the communication makes use of standard formatted blocks called Protocol Data Units (PDU). This gets geeky in a hurry. Rather than write a 2000-word blog entry, I'll just list them:

SPDU
Squitter Protocol Data Unit
Frequencies and slot assignments, plus network maintenance data

PDU (PREAM)
Preamble Data Unit
Basic negotiation of connection - frequency error, station ID, bit rate, etc

BDU
Basic Data Unit
The smallest data block, from which LPDU are built

LPDU
Link Protocol Data Unit
Larger structure, which in turn makes up the largest ones

MPDU
Media Access Protocol Data Unit
Several LPDU concerning login, aircraft ID, and the ACARS message, if any

HFNPDU
High-Frequency Network Protocol Data Unit
Several LPDU, containing all manner of data, most for network maintenance. The most useful to us is HFNPDU PERFORMANCE, which will usually contain the flight number and GPS position of the aircraft.

Here are the ARINC ground stations. Note that some numbers are skipped:

1 San Francisco, CA
2 Molokai, HI
3 Reykjavik, Iceland
4 New York, NY
5 Auckland, NZ
6 Hat Yai, Thailand
7 Shannon, Ireland
8 Johannesburg, S. Africa
9 Barrow, AK
13 Santa Cruz, Bolivia
14 Krasnoyarsk, Russia
15 Al Muharraq, Bahrain
16 Guam
17 Canarias (Canary Islands)