Saturday, May 31, 2008

Digital Mode of the Week: PSK31 (Part 1 - Varicode)

Varicode is a Huffman code for use in PSK31 narrow band teleprinting. PSK31 is a binary phase-shift keyed, 31.35-baud mode designed for direct keyboard-to-keyboard ham contacts. Varicode is integral to the overall concept that made PSK31 so well suited to ham radio, despite this low baud rate. In fact, it was the original name for the whole mode that was proposed in 1998 by its developer, an English ham named Peter Martinez (G3PLX).

Like many "major breakthroughs" in radio, the underlying concept has actually been around a while - in this case, since the Morse code. Morse speeds up transmission by making the more commonly used characters shorter, for example a single dit for E. Morse, like Huffman coding, lends itself to tree-shaped decoding algorithms that save a lot of time. Unlike with Baudot, logic can be designed (including in your brain) that bails out of the loop whenever it detects that a character is complete.

The basic Varicode character set is the same as 7-bit ASCII, but the bits aren't, and the framing is completely different. Throughput is a lot faster than if straight ASCII were being sent and everything else was equal. One consideration, however, is that efficiency goes down in languages other than English, or if the traffic is something other than plain lower case text. Either situation begins to deviate from the designed optimum.

The shortest character is the blank space (a single 1 bit), and second shortest is the lower case e (11). Note that all characters, including nulls, end in a 1. This is due to the technical characteristics of the transmission mode, which we'll talk about next week.

Here's the code. It should look familiar, except for the bits.


Dec . Hex .. Char ... Bit Code
....0 ... 00 ... NUL ... 1010101011
....1 ... 01 ... SOH ... 1011011011
....2 ... 02 ... STX ... 1011101101
....3 ... 03 ... ETX ... 1101110111
....4 ... 04 ... EOT ... 1011101011
....5 ... 05 ... ENQ ... 1101011111
....6 ... 06 ... ACK ... 1011101111
....7 ... 07 ... BEL .... 1011111101
....8 ... 08 ... BS ...... 1011111111
....9 ... 09 ... HT ...... 11101111
..10 ... 0A ... LF ...... 11101
..11 ... 0B ... VT ..... 1101101111
..12 ... 0C ... FF ...... 1011011101
..13 ... 0D ... CR ..... 11111
..14 ... 0E ... SO ...... 1101110101
..15 ... 0F ... SI ....... 1110101011
..16 ... 10 ... DLE ... 1011110111
..17 ... 11 ... DC1 ... 1011110101
..18 ... 12 ... DC2 ... 1110101101
..19 ... 13 ... DC3 ... 1110101111
..20 ... 14 ... DC4 ... 1101011011
..21 ... 15 ... NAK .. 1101101011
..22 ... 16 ... SYN ... 1101101101
..23 ... 17 ... ETB ... 1101010111
..24 ... 18 ... CAN .. 1101111011
..25 ... 19 ... EM ..... 1101111101
..26 ... 1A ... SUB .. 1110110111
..27 ... 1B ... ESC ... 1101010101
..28 ... 1C ... FS ..... 1101011101
..29 ... 1D ... GS .... 1110111011
..30 ... 1E ... RS ..... 1011111011
..31 ... 1F ... US ..... 1101111111
..32 ... 20 ... SP....... 1
..33 ... 21 ... ! ..... 111111111
..34 ... 22 ... " ..... 101011111
..35 ... 23 ... # .... 111110101
..36 ... 24 ... $ .... 111011011
..37 ... 25 ... % ... 1011010101
..38 ... 26 ... & .. 1010111011
..39 ... 27 ... ' ..... 101111111
..40 ... 28 ... ( .... 11111011
..41 ... 29 ... ) .... 11110111
..42 ... 2A ... * .. 101101111
..43 ... 2B ... +... 111011111
..44 ... 2C ... , .. 1110101
..45 ... 2D ... - .. 110101
..46 ... 2E ... . .. 1010111
..47 ... 2F ... / .. 110101111
..48 ... 30 ... 0... 10110111
..49 ... 31 ... 1... 10111101
..50 ... 32 ... 2... 11101101
..51 ... 33 ... 3... 11111111
..52 ... 34 ... 4... 101110111
..53 ... 35 ... 5... 101011011
..54 ... 36 ... 6... 101101011
..55 ... 37 ... 7... 110101101
..56 ... 38 ... 8... 110101011
..57 ... 39 ... 9... 110110111
..58 ... 3A ... : .. 11110101
..59 ... 3B ... ; .. 110111101
..60 ... 3C ... < .. 111101101
..61 ... 3D ... = .. 1010101
..62 ... 3E ... > .. 111010111
..63 ... 3F ... ? .. 1010101111
..64 ... 40 ... @ .. 1010111101
..65 ... 41 ... A... 1111101
..66 ... 42 ... B... 11101011
..67 ... 43 ... C... 10101101
..68 ... 44 ... D... 10110101
..69 ... 45 ... E... 1110111
..70 ... 46 ... F... 11011011
..71 ... 47 ... G... 11111101
..72 ... 48 ... H... 101010101
..73 ... 49 ... I... 1111111
..74 ... 4A ... J... 111111101
..75 ... 4B ... K... 101111101
..76 ... 4C ... L... 11010111
..77 ... 4D ... M... 10111011
..78 ... 4E ... N... 11011101
..79 ... 4F ... O... 10101011
..80 ... 50 ... P... 11010101
..81 ... 51 ... Q... 1111011101
..82 ... 52 ... R... 10101111
..83 ... 53 ... S... 1101111
..84 ... 54 ... T... 1101101
..85 ... 55 ... U... 101010111
..86 ... 56 ... V... 110110101
..87 ... 57 ... W... 101011101
..88 ... 58 ... X... 101110101
..89 ... 59 ... Y... 101111011
..90 ... 5A ... Z... 1010101101
..91 ... 5B ... [ .. 111110111
..92 ... 5C ... \ .. 111101111
..93 ... 5D ... ]... 111111011
..94 ... 5E ... ^ .. 1010111111
..95 ... 5F ... _ .. 101101101
..96 ... 60 ... ` .. 1011011111
..97 ... 61 ... a..... 1011
..98 ... 62 ... b..... 1011111
..99 ... 63 ... c..... 101111
100 ... 64 ... d..... 101101
101 ... 65 ... e..... 11
102 ... 66 ... f..... 111101
103 ... 67 ... g..... 1011011
104 ... 68 ... h..... 101011
105 ... 69 ... i...... 1101
106 ... 6A ... j..... 111101011
107 ... 6B ... k..... 10111111
108 ... 6C ... l..... 11011
109 ... 6D ... m... 111011
110 ... 6E ... n.... 1111
111 ... 6F ... o..... 111
112 ... 70 ... p..... 111111
113 ... 71 ... q..... 110111111
114 ... 72 ... r..... 10101
115 ... 73 ... s..... 10111
116 ... 74 ... t..... 101
117 ... 75 ... u..... 110111
118 ... 76 ... v..... 1111011
119 ... 77 ... w..... 1101011
120 ... 78 ... x..... 11011111
121 ... 79 ... y..... 1011101
122 ... 7A ... z..... 111010101
123 ... 7B ... {..... 1010110111
124 ... 7C ... |..... 110111011
125 ... 7D ... }.... 1010110101
126 ... 7E ... ~..... 1011010111
127 ... 7F .. DEL ... 1110110101

STS-124 Countdown Continues

Launch is still scheduled for around 2104 UTC today (Saturday). The astronauts are presently entering the spacecraft.

Allan Stern has heard Booster Recovery Vessel traffic on 10780 and 5711 kHz.

Wednesday, May 28, 2008

STS-124 Tentative Launch Is Saturday

Shuttle Discovery's STS-124 mission to the International Space Station is scheduled to lift off at 5:02 p.m. EDT [2102 UTC] on Saturday, May 31.

Astronauts arrived at KSC this morning.

NASA will provide continuous online updates, including a webcast and a blog on the STS-124 mission at:
http://www.nasa.gov/shuttle

On launch day, a blog will update the countdown beginning at noon. Originating from NASA's Kennedy Space Center, the blog is the definitive Internet source for information leading up to launch. During the mission, visitors to NASA's shuttle Web site can read about the crew's progress and watch the spacewalks live. As Discovery's flight wraps up, NASA will offer a blog detailing the spacecraft's return to Earth.

Detailed lists of countdown milestones, news briefing times and participants, and hours of operation for Kennedy's news center and media credentialing office are available at:
http://www.nasa.gov/mission_pages/shuttle/news

For NASA TV streaming video, scheduling and downlink information, visit:
http://www.nasa.gov/ntv

Monday, May 26, 2008

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)

Saturday, May 24, 2008

Interesting RTTY Message from KSM 24 May 08

KSM is the commercial station at the Maritime Radio Historical Society, Pt. Reyes, CA (at the old RCA/MCI maritime and point to point site). In cooperation with the Comm Center group on Yahoo!, which is comprised of former or retired military communicators, it broadcast several RTTY/RATT messages in standard military form.

Here's one of the most interesting ones. All net discipline is exactly as received. The "?" character was used in the message to replace ones that aren't in ITA2. Any format changes, such as stripping leading blanks, were done by Blogger, not me:


VV HNA033
RR RUWMKSM
DE RUMLNHA 0033 1410200
ZNR UUUUU
R 200131Z MAY 08
FM COMMCENTER AT YAHOOGROUPS.COM //NNN7DXB//
TO KSM MARINE RADIO SAN FRANCISCO CA //KSM BCST//
BT
UNCLAS
SUBJ: ACP-127 FORMATTED MESSAGE
REF: ACP-127 TAPE RELAY INSTRUCTIONS ( )
1. THIS IS AN EXAMPLE OF A MILITARY MESSAGE FORMATTED IN
THE ACP-127 TELETYPE TAPE RELAY FORMAT THAT WAS IN USE
IN THE US MILITARY PRIOR TO THE MID-1970S. DURING THE 1970S,
THE MILITARY TELETYPE TAPE RELAY SYSTEM, ALSO KNOWN AS
THE ?TORN TAPE RELAY SYSTEM? WAS SLOWLY REPLACED BY THE NEWER
AND FASTER AUTOMATIC DIGITIAL NETWORK, OR ?AUTODIN?.
2. AUTODIN WAS A HIGH-SPEED, HIGH CAPACITY, COMPUTER CONTROLLED
?SUPER TELETYPE? SYSTEM THAT WAS ALSO CAPABLE OF HANDLING
DATA TRAFFIC IN IBM PUNCHED CARD FORM (HOLLERITH CODE), AND
MAGNETIC MEDIA. IT RELIED ON SERVOS AND TAPE DRIVES, AND LATER,
WAS UPGRADED WITH WHAT WE NOW REFER TO AS HARD DRIVES
THAT WERE ABOUT THE SIZE OF WASHING MACHINES. SOME OF
THE MAIN BRAINS IN THE AUTODIN SYSTEM WERE RCA SPECTRE 70


PAGE 2 RUMLNHA0033 UNCLAS
MAIN FRAME COMPUTERS. MOST ARMY AUTODIN FACILITIES WERE
MAINTAINED BY EITHER PHILCO-FORD OR WESTERN UNION UNDER
DOD CONTRACT. AUTODIN ITSELF WAS FINALLY REPLACED ON
SEPTEMBER 30, 2003 BY A NEW MEDIUM CALLED THE DEFENSE
MESSAGING SYSTEM, OR ?DMS?. DMS OFFERS MORE CAPACITY THAN
DID AUTODIN. IT PERMITS ATTACHMENTS, GRAPHICS, MAPS, MAP
OVERLAYS, LETTERS AND NON-MESSAGE CORRESPONDENCE, FILES,
AND EMAIL TRAFFIC TO BE TRANSMITTED IN A SINGLE SECURE SYSTEM
THAT IS WORLDWIDE IN SCOPE AND OPERATION.
3. ACP-127 PROCEDURES HOWEVER, DIDN"T GO AWAY. MOST US
MILITARY TACTICAL CIRCUITS STILL USED ACP-127 FORMATS UNTIL
THE LATE 1980S, UNTIL THE AUTODIN SYSTEM WAS FINALLY
INTEGRATED IN THE FIELD UNITS. NATO UNITS CONTINUED TO USE
ACP-127 FORMATS, SINCE NONE OF THEIR EQUIPMENTS OR SYSTEMS
WERE COMPATIBLE WITH THE US COMPUTERIZED FORMAT. SYSTEM
COMPATIBILITY IN THOSE DAYS WAS CALLED ?INTEROPERABILITY?.
EVEN TODAY, ACP-127 FORMATS CAN STILL BE FOUND IN SOME
NATO COUNTRIES WHERE INTEROPERABILITY ISSUES CONTINUE
TO PERSIST.
4. TRANSMITTED AS AN INFORMATIONAL SERVICE BY THE


PAGE 3 RUMLNHA0033 UNCLAS
COMMCENTER AT YAHOOGROUPS.COM GROUP. ALL MATERIAL
APPEARING HEREIN IS IN THE PUBLIC DOMAIN.
5. SERVICE AND SUPPORT TO THE TROOPS FROM ONE OF THE
US ARMY"S FINEST COMMUNICATIONS OPERATIONS CHIEFS OF
THE 1ST INFANTRY DIVISION (FORWARD), FORMERLY LOCATED
A COOKE BARRACKS, GOEPPINGEN, NEAR STUTTGART, GERMANY.
BT
0033





NNNN

Monday, May 19, 2008

Digital Mode of the Week: PACTOR

PACTOR® (from Latin "the mediator," also a possible play on PACket plus amTOR) was developed by German hams in the early 1990s. It was originally intended to deal with the limitations of packet radio and AMTOR over noisy and fading HF circuits. It has become something of a de facto standard for HF e-mail systems, not only in amateur bands but also in commercial networks used by ships at sea and by nongovernmental organizations working in isolated areas.

PACTOR was originally based on the clever idea of using the good features of HF packet (robust error checking) and of AMTOR/SITOR (tight sync, short packet lengths), while eliminating the bad ones. The data bursts are longer than SITOR's, greatly reducing the timing demands on equipment. The protocol is better suited to HF than AX.25 packet, meaning fewer retries. Much of the time, PACTOR outperforms both modes in real-world band conditions.

The original mode is called PACTOR-I (Roman numeral one). The company has been speeding it up and adding features ever since, to the point where PACTOR-I is now rather slow and primitive by comparison.

PACTOR-I is a half-duplex, synchronous, ARQ mode which uses connections. The initiating station operates in "master" mode, while the called station is the "slave." Stations then take turns as information sending and receiving stations. The receiving station does a Cyclic Redundancy Check (CRC) on the packets, and transmits a brief ACK/NAK Control Signal (CS). In order to speed things up, a system called "memory ARQ" is used to compare packets and reduce repetition. In the original SCS equipment, this feature used an extremely clever analog algorithm.

There is also a PACTOR-I FEC mode. This does not use connections, but something resembling the "unproto" mode in packet. Frames are repeated and padded out with character 21 if nothing is in the send buffer.

PACTOR-I packet lengths are 96 bits in the slow mode (100 baud) and 192 at 200 baud. The modems are able to choose the appropriate data rate based on error responses from the receiver. PACTOR uses online data compression to further speed up throughput. Text is ASCII using Huffman coding (which prints as garbage unless decoded), falling back to straight ASCII when necessary or for calling.

PACTOR-I modulation is frequency-shift keying (FSK/AFSK), 200-Hertz shift. Like packet, the bits are in the state transitions, so it can be successfully tuned in either USB or LSB without changing polarity. For this reason, amateur mailboxes often list PACTOR frequencies by their center of intelligence, between the two original FSK tones, which then are +/- 100 Hz. LSB dial/window reading will then be the center frequency plus the audio center of your modem or software. On USB, you subtract the audio center.

PACTOR-I has been released for use in any 3rd party products, including modems and multimode sound card programs. It can be considered a standard. Everything else, however, remains completely proprietary to SCS, the German company started by PACTOR's inventors, or its licensees. The company has also worked with large commercial networks such as Globe Wireless to adapt PACTOR into even more proprietary modes.

SCS modems are high-end products for professional use, and they are priced accordingly. There has been some criticism from hams that these prices are a bit out of reach for amateurs. SCS has answered with a simplified PACTOR modem, the PTC-IIex, that lists for "only" 614 Euros as opposed to 1025 Euros for the full-featured version. Of course, either of these prices is a steal compared to the staggeringly expensive WAVECOM and HOKA multimode packages that will do all PACTOR's modes.

Out in the real world, PACTOR-I is used mostly for calling. Some people are still reporting traffic in it, but otherwise you'll be able to tell it's PACTOR and grab a callsign or two, then things will get weird in a hurry as the modems adapt. They'll start to switch quickly through a truly bewildering number of highly advanced modes that remain available only in boxes made or licensed by SCS.

PACTOR-II adds several more compression and coding features, and switches the modem to differential phase-shift keying (DPSK) to save spectrum. The sound changes from the well known lazy brrrrrrp brrrrrrp brrrrrrp to various hisses and buzzes usually otherwise heard in advanced military modes. Throughput increases from 100/200 baud to a best case 1200 bits/sec using compression.

The current hot setup is PACTOR-III, which adds yet more features to the firmware in existing SCS modems. Users can try these features for 20 connects, then a license is required. This one goes at a screaming best case throughput of 5200 bits/sec, though in doing so it becomes very wide indeed (2.4 kHz), with 18 tones and a physical bitrate of 3600/sec.

Here's a list of PACTOR modulations:

PACTOR-I:
FSK, 200 Hz, 100/200 baud

PACTOR-II (uncompressed)
2 tone DBPSK, 200 b/s physical, 100 b/s throughput
2 tone DQPSK, 400 b/s, 200
2 tone 8-DPSK, 600 b/s, 400
2 tone 16-DPSK, 800 b/s, 700

PACTOR-III (uncompressed)
2 tones, 200 b/s physical, 76.8 net data rate
6 tones, 600 b/s, 247.5
14 tones, 1400 b/s, 588.8
16 tones, 3200 b/s, 2039.5
18 tones, 3600 b/s, 2722.1

Pactor-III also has many submodes depending on various combinations of tones and DBPSK vs DQPSK.

In all modems, the maximum speed level can be set by the user.


--
Legal note: PACTOR® is a registered trademark of SCS, Germany.
http://www.scs-ptc.com/

Thursday, May 08, 2008

FCC Denies Miller Digital Bandwidth Petition

In a Report and Order in the matter of RM-11392, the FCC has denied a rule making petition by amateur Mark Miller regarding bandwidth and frequencies used for digital modes, especially by automatically controlled stations.

Miller's argument was that the adoption of wideband data and image transmission by new generations of computer-oriented hams would clog the subbands now being used for such older modes as RTTY. He asked for tighter limits on these, more or less rolling back the FCC rules to before 2006. He noted his awareness that this would also effectively ban Pactor-III and ALE, but that was the price of good spectrum management.

Most of the 650 comments were negative, and Miller's filing had been widely derogated as the "digital stone age petition." The FCC agreed that he had not made a good case that rule changes were necessary.

Armed Forces Day SECDEF Message This Saturday

From Army MARS:

SECRETARY OF DEFENSE MESSAGE TEST VIA DIGITAL MODES.
The Secretary of Defense message will be transmitted via digital modes including RTTY, PACTOR, AMTOR, PSK-31, MFSK and MT63 from the stations listed below, including frequencies, mode, and date/time in Zulu (UTC). All frequencies are listed for center of intelligence. Offset as appropriate for your TNC. (Note: Not all stations may necessarily operate on all the frequencies listed, depending on propagation and available equipment.)

Army Stations

STATION: AAZ (HQ Army MARS Gateway, Fort Huachuca, Arizona)

6988.0 kHz
RTTY 11 May 0110Z
PACTOR FEC 11 May 0130Z
MT63 11 May 0220Z
PSK-31 11 May 0250Z
14402.0 kHz
RTTY 11 May 0110Z
PACTOR FEC 11 May 0130Z
MT63 11 May 0220Z
PSK-31 11 May 0250Z

STATION: WAR (Pentagon ARC/MARS Station, Arlington, Virginia)

6988.0 kHz
RTTY 10 May 1700Z
RTTY 10 May 2300Z
MT63 10 May 1715Z
MT63 10 May 2315Z
14440.0 kHz
PACTOR FEC 10 May 1730Z
PACTOR FEC 10 May 2330Z
Olivia 10 May 1745Z
Olivia 10 May 2345Z
Stations copying the Secretary of Defense message transmitted from AAZ/WAR should send their entries to Armed Forces Day Celebration, Commander NETCOM/9th ASC, Attn: NETC-OPE-MA (MARS) (31), Fort Huachuca, AZ 85613-5000.

Air Force Stations

STATION: AIR-2 (Scott Air Force Base)

7831.1 kHz
RTTY 10 May/1930Z
PACTOR 10 May/2000Z
MT63 10 May/2030Z
MFSK 10 May/2100Z
14877.1 kHz
RTTY 10 May/2130Z
PACTOR 10 May/2200Z
MT63 10 May/2230Z
MFSK 10 May/2300Z

Navy/Marine Corps Stations

STATION: NAV (HQ NAVMARCORMARS Radio Station, WILLIAMSBURG, VA)

7346.5 kHz
RTTY 75 baud 10 May/2340Z
AMTOR FEC 11 May/0010Z
MT63 11 May/0040Z
14480.0 kHz
RTTY 75 baud 10 May/2340Z
AMTOR FEC 11 May/0010Z
MT63 11 May/0040Z

STATION: NAV3 (NAVMARCORMARS Radio Station, CORPUS CHRISTI, TX)

7393.0 kHz
RTTY 10 May/2340Z
AMTOR FEC 11 May/0010Z
MT63 11 May/0040Z
13975.5 kHz
RTTY 10 May/2340Z
AMTOR FEC 11 May/0010Z
MT63 11 May/0040Z

STATION: NAV4 (NAVMARCORMARS Radio Station, GREAT LAKES, IL)

7375.0 kHz
RTTY 11 May/0240Z
AMTOR FEC 11 May/0310Z
MT63 11 May/0340Z
14468.5 kHz
RTTY 11 May/0240Z
AMTOR FEC 11 May/0310Z
MT63 11 May/0340Z

STATION: NBL (NAVMARCORMARS Radio Station, GROTON, CT)

7370.0 kHz
RTTY 10 May/2340Z
PACTOR FEC 11 May/0010Z
AMTOR FEC 11 May/0040Z
14393.0 kHz
RTTY 10 May/2340Z
PACTOR FEC 11 May/0010Z
AMTOR FEC 11 May/0040Z

STATION: NPL (NAVMARCORMARS Radio Station, SAN DIEGO, CA)

7350.0 kHz
RTTY 11 May/0240Z
PACTOR FEC 11 May/0310Z
AMTOR FEC 11 May/0340Z
14465.0 kHz
RTTY 11 May/0410Z
PACTOR FEC 11 May/0440Z
AMTOR FEC 11 May/0510Z

STATION: NUW (NAVMARCORMARS Radio Station, NAS WHIDBEY
ISLAND, WA)

7380.0 kHz
RTTY 11 May/0240Z
PACTOR FEC 11 May/0310Z
AMTOR FEC 11 May/0340Z
13530.0 kHz RTTY 11 May/0410Z
PACTOR FEC 11 May/0440Z
AMTOR FEC 11 May/0510Z

SUBMISSION OF SECRETARY OF DEFENSE TEST MESSAGE ENTRIES.

Transcripts of the RTTY, PACTOR, AMTOR, PSK-31, MFSK and MT63 receiving test should be submitted "as received". No attempt should be made to correct possible transmission errors. Provide time, frequency and call sign of the military station copied, including name, call sign, and address (including ZIP code) of individual submitting the entry. Ensure this information is placed on the paper containing the test message. Each year a large number of acceptable entries are received with insufficient information, or necessary information was not attached to the transcriptions and was separated, thereby precluding issuance of a certificate. Entries must be sent to the appropriate military address as follows:

a. Stations copying Secretary of Defense message transmitted from AAZ send entries to:
Armed Forces Day Celebration
Commander NETCOM/9th ASC
Armed Forces Day Celebration
Attn: NETC-OPE-MA (MARS) (31)
Fort Huachuca, AZ 85613-5000
b. Stations copying Secretary of Defense message transmitted from NAV, NAV-3, NAV-
4, NBL, NPL or NUW send entries to:
Armed Forces Day Celebration
Chief, Navy-Marine Corps MARS
Cheatham Annex Bldg 117
108 Sanda Ave
Williamsburg, VA 23185-5830
c. Stations copying Secretary of Defense message transmitted from AIR-2 send entries
to:
Armed Forces Day Celebration
AFCA / Chief, AF MARS
203W Losey St
Scott AFB, IL 62225

Details of the amateur crossband transmitting test are here.

US Army Corps of Engineers QSL Opportunity

From Jim Pogue:

Once again, station WUG-231 will offer a special QSL card for SWLs only who hear our station during the ANNUAL ARMED FORCES DAY CROSSBAND MILITARY/AMATEUR RADIO COMMUNICATIONS TEST this Saturday, 10/11 MAY 2008.

Any SWL worldwide who hears us is invited to send a reception report and receive our special commemorative QSL card. This will be different than the one amateurs receive for any contacts they make with us.

You may send your report directly to me at the address below. No return postage is necessary. Frequencies are also listed below. Good luck and I hope to hear from you.

STATION: WUG-231 (10 May 1300Z - 11 May 0200Z)

Frequency Emission Amateur Band
4032.9 kHz LSB 80M
7.360.0 kHz LSB 40M
6.826.0 kHz LSB 40M
14486.0 kHz USB 20M
14663.5 kHz USB 20M
20973.5 kHz USB 15M

Location: Memphis, TN
Address:
USACE Memphis District Office
ATTN: Jim Pogue
Public Affairs Office Room B-202
167 N. Main St.
Memphis, TN 38103-1894

POC: Mr. Jim Pogue
Commercial: (901) 544-4109

[Editor's note: the annual Armed Forces Day crossband tests are done a week before AFD, so as not to conflict with the Dayton Hamvention.]

Digital Mode of the "Week:" HF Packet

This is early because I'm going on vacation.

---

"Packet Radio" is an amateur mode used to send data between terminals attached to radios. It really took off in the 80s after the authorization of ASCII on amateur bands. It gets its name from "packet switching," a networking protocol in which data is divided into small blocks (packets) with the address and sequence numbers attached. This allows a station to act as a "node," and connect to multiple users on the same frequency. Incidentally, you're using packet-switching and routing right now, since these are also used in the TCP/IP protocol suite which makes the Internet go.

HF packet, which is what we're interested in, is an adaptation of the VHF packet you might be more used to. It transmits at 300 baud, with a 200-Hz shift, using audio frequency-shift keying (AFSK) of standard single-sideband ham transceivers. Various tone centers have been used by different hardware Terminal Node Controllers (TNCs), with the most common being 2210 and 1700.

The AX.25 link-layer protocol used by amateur packet radio uses a special polarity (or lack therof) called NRZI (Non-Return to Zero Inverted). In this, any bit state transition is a one, and no transition is a zero. Since it's the transitions that matter, mark and space are in practice not relevant. This means that packet can be tuned in USB or LSB with no need to change polarity at the receiver. However, as in RTTY, the receiver dial frequencies are usually (though not always) closer to the listed ones in LSB mode.

Today, software TNCs have pretty much replaced hardware ones, but the underlying link-layer scheme is the same. It's just better hidden. AX.25 uses connections, meaning that one station will connect with the other before exchanging information. However an "unproto" mode is provided for CQs, and a "beacon" mode for all-station-this-net broadcasts. There's also a "monitor" mode, which is what we will use, because it decodes all the packets.

Packets are labeled for type of data, which for our purposes means that they are either control packets or data packets. A lot of control packets are sent, giving the mode a rather high overhead.

The receiving connected station will error-check packets and ask for retries of missed ones. Therefore packet radio, like SITOR-A, slows down as channel noise increases. Even at 300 baud, the need for retries can make real information throughput absolutely glacial, and HF packet just isn't used much for long messages. In extensive monitoring, I've seen a few BBS (Bulletin Board System) connections, a few compressed file transfers (which print as gibberish), and a lot of automatic forwarding of packets (aka "digipeating").

Plain text is 7-bit ASCII. TNCs can switch to 8-bit mode for binary transfers or extended characters, but the one at the other end has to do same.

HF packet sounds like a series of short buzzes. These are much shorter and chirpier sounding than other modes used for e-mail and such. Given the greater chance that long packets will be rejected, it's best to keep the bursts very short.

One interesting mode that is run as an application on top of packet is Automatic Position Reporting System (APRS). This automatically sends the GPS position of the station, or even such data as the weather. It allows hams to track vehicles out in the boonies, or participate in weather observing networks. These are then forwarded to multiple stations, and plotted using slick map software. Obviously, HF has considerable potential here due to its coverage of areas where VHF is unheard of.

The best HF frequency for APRS is listed as 10147.6 USB. This is the worldwide APRS gateway. My receiver gives a 1700-Hz tone center when tuned in this mode. I have it on right now, and an HF station just reported a position in California. This is cool stuff.

Sunday, May 04, 2008

Digital Mode of the Week: ASCII

ASCII stands for American Standard Code for Information Interchange. It was developed in the United States as a standard means of encoding text readable by people as bits readable by digital computers. It gradually replaced other such American codes as IBM's EBCDIC and Commodore's PETSCII. US ASCII is something of a de facto standard worldwide.

You're using ASCII right now. It's still the basis for most of the text characters used by computers, although as a subset of several much larger character sets that are now used. Plain text files are still usually straight ASCII. It's still fundamental to most of our digital modes.

ASCII was originally developed at Bell Labs for use with wireline TWX machines (an AT&T version of the Teletype). It is essentially an expansion and reordering of ITA2 to make it more useful to computers or "dumb" terminals with modems attached. Today's ASCII is a 7-bit asynchronous code with 128 characters (starting at zero). The first 33 characters (0-32) are non-printing, consisting of null (all zeroes) plus a number of control codes, and the space/blank character (decimal 32).

ASCII can, of course, be sent by frequency-shift keying, and in fact it wasn't long before hams investigated its use as an improvement to radioteletype (RTTY). However, its greater complexity and speed made results on noisy HF circuits disappointing at best when just using straight ASCII. Instead, it's usually sent by packet radio or other error-checking teleprinting schemes.

ASCII characters are sent with "framing" consisting of one start bit and one or two stop bits (remember Baudot's use of a longer stop). Characters usually map to bytes, and since these have 8 bits in modern computers, there's a bit left over. Various things are done with this extra bit.

Many modems have the option to use this 8th bit as a parity bit. This gives a rudimentary error check. If parity is used, the 8th bit will be set or unset so that every character has an even number of ones (even parity) or an odd number (odd parity). If parity is turned off on 7-bit ASCII, the receiver will (hopefully) ignore the 8th bit.

The 8th bit is also used to expand the character set to the full 255. Although SHIFT IN and SHIFT OUT are provided, setting this bit can also send the expanded characters, essentially treating ASCII as an 8-bit code with no parity check.

Unfortunately, there's no international standard for this, and technically it's something of a misnomer to apply the name ASCII to all 8 bits. The high-bit characters are often dependent on application. They can contain accented letters and symbols used in a particular language, or little pieces of lines and corners useful for drawing boxes on old text based terminals.

All of this leads to those infamous ASCII receiver setup parameters that are used in most of our digital modes. These are character length (7 or 8 data bits), stop bits (one or two), and parity (odd, even, or none). While some straight ASCII software can autobaud, it's usually also necessary to set the baud rate by hand. Common HF rates are 100, 110, 300, 600, 1200, 1800, and 2400.

Usually getting all this right in a short wave listening situation is by trial and error. It helps that there are really only two settings in common use. These are 7E1 (7 data bits, even parity, one stop bit), and 8N1 (eight data bits, no parity, one stop bit). It is also possible to emulate the old ITA2 alphabet by simply transmitting the appropriate character set in 5N1 or 5N2 (5 data bits, no parity, one or two stop bits). You see this done by the French Navy when sending data in newer modes such as STANAG 4285.

Here's the 7-bit ASCII in a compact table found on Wikipedia:



An expanded listing of this code is at this column's web site.

Saturday, May 03, 2008

KSM Encrypted Broadcast WILL Take Place May 3

KSM's intrepid transmitter engineer has recovered sufficiently to come to the station and make the encrypted RTTY and SITOR-B broadcasts using a classic US military crypto machine from World War II. Details are as follows:

Times: Approximately 1900 and 2100 UTC on May 3.

Assigned frequencies: 8433.0 and 12631.0.

Modes: RTTY and FEC. Baudot transmissions are at 170cps shift, 45 baud. FEC transmissions are at 170cps shift, 100 baud (SITOR-B).

Text will start with a plaintext preamble and will include the settings for the M-209 as well as the key. That will be followed by the encrypted text in five letter groups. Since hardly anyone has an M-209, a software emulator is available here. I have been playing with this, and it's a very slick program.

K6KPH will guard its usual CW frequencies of 7050, 14050, 21050 (3550 on request). Since these frequencies are in the scan with the ship calling frequencies the best bet is to use commercial calling procedure: repeat "K6KPH" (within the limits of FCC identification requirements of course) until the K6KPH operator responds with "DE", then send your call and traffic.

QSL, as always, is to Denice Stoops, PO Box 381, Bolinas, California 94926 USA.

Maritime Radio Historical Society web site

Friday, May 02, 2008

IARU Simulated Emergency Test Is May 3

For us, the most interesting feature of this event is the use of Automatic Link Establishment on amateur frequencies. From International Amateur Radio Union:

Operators participate in the Global Simulated Emergency Test by sending ALE text messages to the central IARU GlobalSET European headquarters relayed via the network of ALE Global HFN Pilot Stations. Hams activate their ALE stations, start scanning and sounding before the event, and send messages during the day of the event. In addition to the emergency practice, this provides valuable
knowledge of the resources that can be mobilized in the event of a real emergency.


HFN is the amateur Global High Frequency Network. The network frequencies and pilot stations are:

3596.0
7102.0
10145.5
14109.0
18106.0
21096.0
24926.0
28146.0

ALE Net: HFN
SLOT
1 [ User's callsign ]
2 KM4BA
3 KQ6XA
4 WA3MEZ
5 K7EK
6 VE2FXL
7 NJ7C
8 WD8ARZ
9 KN0CK
10 N0PWZ

Amateurs will attempt to link up with these stations and pass their emergency power capability in an AMD (Automatic Message of the Day).

While it is not clear, presumably May 3 begins at 0000 UTC, which is on the 2nd in the US. In fact, it is about an hour from this posting.

A "qrg" (frequency) file is available at hflink.com. If you join their Yahoo! group, you can also get the latest version of PC-ALE, which will scan (MultiPSK and SkySweeper won't). I've got it going here, and it seems much more sensitive than previous versions. Thanks to the hflink administrators for making it available to me.

It is important NOT to attempt to transmit ALE with amateur equipment unless you know what you are doing. It's not designed to change bands this fast unless you are using a good autotuner and antenna(s) for all bands. In addition, the amateur rules impose certain technical issues. Read the materials out on the Internet before trying this mode!!!!!!

US/NATO Joint Exercise On Until May 14

From Combinedendeavor.net


Welcome to Combined Endeavor 2008!

This annual, United States European Command (USEUCOM)-sponsored exercise is “in the spirit of” the Partnership for Peace (PfP) C4 Integration and Interoperability Exercise. CE enables interoperability between U.S. and NATO / PfP military C4 equipment by documenting and exercising technical and procedural solutions.


What this means in standard English is that this annual communication/ interoperability exercise always brings out some good (often unencrypted) digital military exercise traffic in Europe.

Thursday, May 01, 2008

Charles Brain's Web Site Vanishes

Those looking for Charles Brain's web site with the "official" distributions of PC-ALE and PC-HFDL got a rude surprise today when it vanished. Those taking the link got a blank white page with the cryptic, "I am sorry but my website got deleted."

The last "official" stable release of PC-HFDL, version 2.031, is still available on this column's web site. It was put there originally by request of Charles to help with his bandwidth issues, and it is a copy of the official msi file in a zip folder.

Since the beta 2.04 was never "officially" released, I won't put it up unless asked to, even though I have the distribution zip archive, and the program has always worked just fine here.

The latest stable, non-MARS version of PC-ALE is 1.062G. There's a beta of 1.062H available here. This one is really intended for amateur radio use, though I have gotten it to work for utilities simply by changing the frequencies and group names in the QRG file. There has been some grumbling about this program by those who preferred the old, terse, rather inscrutable user interface. However, it's the one in use here.

While checking all this, I notice that the frequency 14109.0 is now the amateur ALE "pilot channel," though 14109.5 will be scanned until July of 2008.

Pacific Air Route Map

This was made by plotting several hundred aircraft position reports with PC-HFDL and Posfix, then layering the resulting maps with Photoshop. The result was a clear indication of the routes taken by airplanes between the US mainland and Hawaii. These were traced over on a new layer. Then the Posfix plots were dropped out, and the original map was combined with the new darkened lines, and saved as a new Posfix map. Subsequent plots have all been right on.