Recently, I read a rather impromptu test done by WZ7I. It seemed to indicate that a popular ham program called TrueTTY actually had better "sensitivity" than a tweaked version of the older MMTTY, which I'd always figured was the hot setup.
This got me interested, since I'd used TrueTTY in the past, and liked it. So I went to the DXSoft site where the clever Russian programmer Sergei Podstrigailo, UA9OSV, has his latest stuff.
What I noticed, though, is that his other NBDP program, called SeaTTY, was starting to look like a better deal for users who wanted to concentrate on receiving, especially in the maritime bands. Needless to say, I grabbed it, in version 2.30.
SeaTTY looks like TrueTTY, with the same sleek user interface showing the FFT amplitude plot at the top and the bit scope at the bottom. Its purpose, though, is not making ham QSOs. It's listed as a "weather messages decoder," and indeed it's set up to facilitate the unattended grabbing and filing of same.
Modes decoded are RTTY, Navtex/ Sitor-B, DSC (HF/VHF), HF FAX, and NWR-SAME. The latter is a VHF signaling mode used by weather broadcasts to target specific areas.
I put SeaTTY to work on the longwave RTTY weather broadcast from Hamburg/Pinneberg Meteo in Germany, as received by the WebSDR in the Netherlands. It started up, spat out a few garbage characters, then happily produced a steady 100% decode. I ran MMTTY and SkySweeper alongside, and MMTTY was also 100%. SkySweeper was good, but produced the inexplicable character errors I've come to expect from its RTTY mode.
This was too easy. I waited for propagation, and gave it the RTTY weather from CFH in Halifax, NS. This is never a good path to SoCal, and the geomagnetic storm had left some extra fading. Interestingly, SeaTTY and MMTTY produced about the same percentage of characters decoded, but messed up in different places. While the decode rate was about the same, SeaTTY actually produced somewhat more readable copy.
SeaTTY was about as good as DSCDecoder on Navtex and HF Sitor-B weather. It files successful Navtex decodes in a slick directory tree structure, with the copy showing in a window alongside. The save is automatic, as long as the Telex start code (ZCZC) and end code (NNNN) are detected.
DSC decode shows as a numeric dump of the raw symbols, but clicking the time stamp produces the message. The only missing feature compared to DSCDecoder is the instant lookup of MMSI numbers in the ITU database.
Where I really had fun, though, was the FAX. It's a very well thought out interface for this mode. Finally, there's a FAX decoder as intuitive and generally slick as the old JVComm, but which doesn't print "Demo" all over your faxes until you pony up. (SeaTTY, like DSCDecoder, waits a set number of days, then sulks until you pay. It's $35 and easy to register.)
I'd long since learned how to play SkySweeper's fax interface like a musical instrument, and turn out awesome copy, but right now I think I'll switch to SeaTTY. Once I get used to it, I suspect it'll be just as good, and with less general fuss to get working. Faxes, like Navtex messages, get time stamped and autosaved, accessible from the directory tree. Good stuff.
To sum up, SeaTTY is a keeper. I gladly paid up. Now I go forth into the Ether with some good tools.
Showing posts with label RTTY. Show all posts
Showing posts with label RTTY. Show all posts
Monday, August 09, 2010
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
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
Saturday, April 26, 2008
No KSM RTTY Today
As you might have noticed, there was no RTTY or FEC SITOR from KSM on Point Reyes, CA today. Your radio is fine. They didn't transmit it. This means the encrypted text was not sent, and those of us who were waiting with virtual cipher machines at the ready will just have to wait another week.
The broadcast had to be cancelled due to illness of the engineer who does the RTTY. They will try again next Saturday, May 3. Times and frequencies are still the same as the ones mentioned below.
The broadcast had to be cancelled due to illness of the engineer who does the RTTY. They will try again next Saturday, May 3. Times and frequencies are still the same as the ones mentioned below.
Thursday, April 24, 2008
KSM Encryption/ Decryption Exercise 4/26 and 5/3
KSM, a licensed commercial station using vintage equipment and antennas at historic KPH on Pt. Reyes, CA, will be doing a very interesting broadcast in World War II M-209 encryption. It's at 1900 and 2100 UTC on April 26 (also International Marconi Day) and a week later on May 3. The key will be broadcast, and listeners are invited to attempt decryption of the message with readily available freeware.
M-209, for those of us who weren't born yet, is a US military mechanical code machine slightly resembling a 6-rotor, patch board-less version of the better known German ENIGMA.
Here's the full release from Richard Dillman of MRHS:
M-209, for those of us who weren't born yet, is a US military mechanical code machine slightly resembling a 6-rotor, patch board-less version of the better known German ENIGMA.
Here's the full release from Richard Dillman of MRHS:
KSM will broadcast messages encrypted with the military M-209 crypto machine via RTTY on 26 April and 3 May.
The idea for the broadcast came up in conversations between myself and Dave Ross as a way for the MRHS to support the Military Radio Collectors Group meet taking place in San Luis Obispo, CA on 2-3 May. We thought it would be fun to give the attendees something to copy on their vintage military RTTY gear and then exercise their M-209 skills by decoding the message. But we thought other listeners may enjoy trying their hand at decoding the message as well, thus this announcement (see below for information about a M-209 emulator in case you don't have access to the genuine article).
MRHS transmitter engineer Steve Hawes, who manages our RTTY broadcasts, was keen for the idea and Dave provided the text so all the pieces are in place. Here are the details:
Dates: 26 April and 3 May
Times: Approximately 1200pdt and 1400pdt
Modes: RTTY and FEC. Baudot transmissions are at 170cps shift, 45 baud. FEC transmissions are at 170cps shift, 100 baud
Frequencies: 8433.0kc, 12631.0kc
Text: Dave's 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.
Additional information:
MRCG - http://syzen.com/milradio/
M-209 emulator for those who wish to participate but don't have a M-209 -
http://users.telenet.be/d.rijmenants/en/m209sim.htm
MRHS - http://www.radiomarine.org
Sunday, April 20, 2008
Digital Mode of the Week: RTTY (Part 2: Teleprinting over radio)
Having discussed the origins of the 5-bit teleprinting ("Baudot") code, now we can talk about one of the oldest digital modes. This is RTTY, for radioteletype. It has undergone several incarnations, from wire teleprinting (like news wires), through various types of hardware-based radio modems, and finally to just another digital option in multimode computer sound card packages.
RTTY is sent over the radio by keying a transmitter between two tone frequencies corresponding to binary states. These are called mark and space. The process is called frequency-shift keying (FSK, F1B emission).
Direct FSK is still used in some dedicated RTTY equipment, but audio frequency-shift keying (AFSK) is far more common today. It is done by generating the proper modulation of an audio tone, which is then sent to the audio input of a standard single-sideband voice radio. (Note that power is lowered due to RTTY having a continuous duty cycle.)
Either method produces the same signal in the receiver. To the ear, RTTY sounds like a continuous warbling tone with rather clicky bit transitions, and often kind of a busy, chattery pulsation to it.
The difference between mark and space frequencies is the shift (in Hz), and the number of bit transitions sent in a second is the speed (in baud). Sometimes you also see speed in words per minute.
Common speeds are 45 (actually 45.45), 50, and 75. Common shifts are 170, 450, and 850. Characters are sent asynchronously, as they are generated. The five data bits are preceded by a single start bit and then followed by 1, 1.5, or two stop bits. (In practice, a long stop bit just sounds like a brief pause on the tone, making RTTY sound even more chattery.)
RTTY's standard tone center (halfway between mark and space) varies a bit. For the most part, it's around 2210 Hz. RTTY used to require careful tuning to center the tones on their respective filters, but today's decoders are more forgiving. Usually, one simply clicks on or between the two peaks on a display, or the software jumps to the loudest signals. The tone center is sometimes relevant for frequency logging, however.
RTTY dial vs listed frequencies can get pretty ambiguous. One can easily be 2 or more kHz off, and not even be sure which way. If you hear nothing on the listed frequency, tune around.
The third important parameter is signal polarity, which can be "normal" or "reverse." This refers to whether mark or space is the lower of the two tones, preferably when tuned in LSB. Unknown signals require some trial and error to find the speed and polarity which print readable text. Shift is usually more evident.
RTTY has no error check, meaning that any problems with the signal will create gibberish, or no print at all. Missed characters on fades are just something we live with.
The good news is that RTTY may be primitive, but it's still heard all over the HF bands. The bad news is that most of this is encrypted, often in a secure military/ government mode called KG-84. There is absolutely no way to get meaningful copy from it. A few navies, particularly the French, still run RTTY test loops and an occasional real message in the clear. Remaining weather stations in Germany and Canada have regular RTTY schedules.
RTTY in the military can also be referred to as RATT.
Old time RTTY stations stored messages on long reels of perforated paper tape, a character at a time. A procedure named "tape relay" existed for the storage and forwarding of traffic. Tapes were punched by perforating devices attached to Teletype machines, for transmission later. Received traffic could be punched directly onto this tape by a reperforator, and relayed by sending the tape to a reader. Much of RTTY's operating nomenclature such as "brag tapes," "test slips," and "loops," is a holdover from this era.
1950s US Navy tape position
The American Radio Relay League (ARRL) headquarters station W1AW sends long RTTY bulletins daily, on time/frequency schedules listed all over the Internet. Shorter transmissions, by hams shooting the breeze or in operating contests, can be heard up or down maybe 10-15 kHz from 14080.
RTTY is sent over the radio by keying a transmitter between two tone frequencies corresponding to binary states. These are called mark and space. The process is called frequency-shift keying (FSK, F1B emission).
Direct FSK is still used in some dedicated RTTY equipment, but audio frequency-shift keying (AFSK) is far more common today. It is done by generating the proper modulation of an audio tone, which is then sent to the audio input of a standard single-sideband voice radio. (Note that power is lowered due to RTTY having a continuous duty cycle.)
Either method produces the same signal in the receiver. To the ear, RTTY sounds like a continuous warbling tone with rather clicky bit transitions, and often kind of a busy, chattery pulsation to it.
The difference between mark and space frequencies is the shift (in Hz), and the number of bit transitions sent in a second is the speed (in baud). Sometimes you also see speed in words per minute.
Common speeds are 45 (actually 45.45), 50, and 75. Common shifts are 170, 450, and 850. Characters are sent asynchronously, as they are generated. The five data bits are preceded by a single start bit and then followed by 1, 1.5, or two stop bits. (In practice, a long stop bit just sounds like a brief pause on the tone, making RTTY sound even more chattery.)
RTTY's standard tone center (halfway between mark and space) varies a bit. For the most part, it's around 2210 Hz. RTTY used to require careful tuning to center the tones on their respective filters, but today's decoders are more forgiving. Usually, one simply clicks on or between the two peaks on a display, or the software jumps to the loudest signals. The tone center is sometimes relevant for frequency logging, however.
RTTY dial vs listed frequencies can get pretty ambiguous. One can easily be 2 or more kHz off, and not even be sure which way. If you hear nothing on the listed frequency, tune around.
The third important parameter is signal polarity, which can be "normal" or "reverse." This refers to whether mark or space is the lower of the two tones, preferably when tuned in LSB. Unknown signals require some trial and error to find the speed and polarity which print readable text. Shift is usually more evident.
RTTY has no error check, meaning that any problems with the signal will create gibberish, or no print at all. Missed characters on fades are just something we live with.
The good news is that RTTY may be primitive, but it's still heard all over the HF bands. The bad news is that most of this is encrypted, often in a secure military/ government mode called KG-84. There is absolutely no way to get meaningful copy from it. A few navies, particularly the French, still run RTTY test loops and an occasional real message in the clear. Remaining weather stations in Germany and Canada have regular RTTY schedules.
RTTY in the military can also be referred to as RATT.
Old time RTTY stations stored messages on long reels of perforated paper tape, a character at a time. A procedure named "tape relay" existed for the storage and forwarding of traffic. Tapes were punched by perforating devices attached to Teletype machines, for transmission later. Received traffic could be punched directly onto this tape by a reperforator, and relayed by sending the tape to a reader. Much of RTTY's operating nomenclature such as "brag tapes," "test slips," and "loops," is a holdover from this era.
1950s US Navy tape position
The American Radio Relay League (ARRL) headquarters station W1AW sends long RTTY bulletins daily, on time/frequency schedules listed all over the Internet. Shorter transmissions, by hams shooting the breeze or in operating contests, can be heard up or down maybe 10-15 kHz from 14080.
Sunday, April 13, 2008
Digital Mode of the Week: RTTY (Part 1: ITA2 Telegraphic Alphabet)
We begin a new Utility World series of basic descriptions of digital modes you hear on the air.
First up is one of the oldest modes, but it is still used widely. It's usually called RTTY, for Radioteletype. In the military, you'll also see references to RATT, also Radioteletype.
RTTY's earliest precursor is the Baudot telegraphy code developed in the 1870s by two people working for Jean-Maurice-Émile Baudot, a French engineer. (Yes, that's where we get the transmission speed unit "baud.") This was a 5-bit code, that became known as International Telegraph Alphabet #1 (ITA1, no longer used).
The Baudot code was improved by Donald Murray and others in the early 20th century, leading to an originally Western Union wireline standard called ITA2. This is still the one used for basic English-language Baudot teleprinting. It is still a 5-bit, 32-state, 58-character code, with longer pauses marking start and stop of characters. The name "Baudot" for ITA2 is not technically correct, but in practice the two names are interchangeable. Several ITA alphabets with higher numbers exist for use in other languages, and of course we don't even have time to talk about "third shift" modes for such non-Latin character set languages as Russian.
ITA2 has no lower case. The cases are LTRS (Letters; all upper case) and FIGS (Figures; numbers and punctuation). The case is changed by transmission of control characters corresponding to each. Since the normal mode is letters case, they can also be regarded as shift in (to figures) and shift out. A missed shift character leads to gibberish, and most RTTY systems have the option USOS (Unshift On Space) as a partial (and only partial) solution.
ITA2 bit states are based on timing, and they do not correspond to the base-2 places used in binary numerical notation, which was not used in mechanical teleprinting. Since a bit is technically a "binary digit," we should probably be calling them something else, but we won't. However, note how many of the ITA2 control characters carried over, with bit changes, into later binary computer codes such as American Standard Code for Information Interchange (ASCII).
The 5 bits were typically stored by punching holes in paper tape run through a perforator machine from reels resembling 16-mm movie film. These were read by tape keyers, which controlled a "current loop" connected to a "terminal unit" that interfaced with mechanical teleprinting machines. Many of these were made by the Teletype Corporation, and so "Teletype" is actually an old business trade name, though it has become somewhat generic.
Messages could be relayed by "reperforating" at the receive site. Note that the character pair RY is sent with alternating 01010 and 10101, testing all possible bit states in the code. Even in this electronic age, the test "slip" RYRYRY..., sometimes accompanied by THE QUICK BROWN FOX... is still common.
Here is the ITA2 code (click for bigger image):
First up is one of the oldest modes, but it is still used widely. It's usually called RTTY, for Radioteletype. In the military, you'll also see references to RATT, also Radioteletype.
RTTY's earliest precursor is the Baudot telegraphy code developed in the 1870s by two people working for Jean-Maurice-Émile Baudot, a French engineer. (Yes, that's where we get the transmission speed unit "baud.") This was a 5-bit code, that became known as International Telegraph Alphabet #1 (ITA1, no longer used).
The Baudot code was improved by Donald Murray and others in the early 20th century, leading to an originally Western Union wireline standard called ITA2. This is still the one used for basic English-language Baudot teleprinting. It is still a 5-bit, 32-state, 58-character code, with longer pauses marking start and stop of characters. The name "Baudot" for ITA2 is not technically correct, but in practice the two names are interchangeable. Several ITA alphabets with higher numbers exist for use in other languages, and of course we don't even have time to talk about "third shift" modes for such non-Latin character set languages as Russian.
ITA2 has no lower case. The cases are LTRS (Letters; all upper case) and FIGS (Figures; numbers and punctuation). The case is changed by transmission of control characters corresponding to each. Since the normal mode is letters case, they can also be regarded as shift in (to figures) and shift out. A missed shift character leads to gibberish, and most RTTY systems have the option USOS (Unshift On Space) as a partial (and only partial) solution.
ITA2 bit states are based on timing, and they do not correspond to the base-2 places used in binary numerical notation, which was not used in mechanical teleprinting. Since a bit is technically a "binary digit," we should probably be calling them something else, but we won't. However, note how many of the ITA2 control characters carried over, with bit changes, into later binary computer codes such as American Standard Code for Information Interchange (ASCII).
The 5 bits were typically stored by punching holes in paper tape run through a perforator machine from reels resembling 16-mm movie film. These were read by tape keyers, which controlled a "current loop" connected to a "terminal unit" that interfaced with mechanical teleprinting machines. Many of these were made by the Teletype Corporation, and so "Teletype" is actually an old business trade name, though it has become somewhat generic.
Messages could be relayed by "reperforating" at the receive site. Note that the character pair RY is sent with alternating 01010 and 10101, testing all possible bit states in the code. Even in this electronic age, the test "slip" RYRYRY..., sometimes accompanied by THE QUICK BROWN FOX... is still common.
Here is the ITA2 code (click for bigger image):
Saturday, September 01, 2007
KSM RTTY Testing Again Today
From Richard Dillman of MRHS:
Once again this Saturday the KSM Transmitter Department plans to exercise the 12Mc RTTY transmitter beginning at about 2000Z and ending at about 2300Z. Press and weather will be broadcast in Baudot and FEC modes.
The Baudot transmission will be 170cps shift, 45.45 baud. The frequency is 12631.0kc.
The tubes currently in the transmitter limit power output to 2.5kW. Once these are replaced a power output of 4 to 5kW will be used. The antenna is a H over 2.
The transmitter for our 8Mc RTTY frequency is undergoing restoration by the Transmitter Department. Once this transmitter operational both 8Mc and 12Mc will be active each Saturday with press and weather information of interest to the maritime community. The 8Mc frequency is 8433.0kc. A double extended Zepp will be used on this frequency.
KSM will be active on Morse as usual on:
426
500
4350.5
6474.0
8438.3
12993.0
16914.0
K6KPH will guard 7050kc and 14050kc for signal reports, NTS traffic and general calls. Since the above frequencies are in a scanner along with the ship calling frequencies, the best procedure to use when calling K6KPH is the same as that for commercial operations: Keep sending "K6KPH" on the above frequencies (within the limits of FCC identification requirements of course). When your call is heard K6KPH will send "DE" after which you can send your call sign. Sometimes things get busy at the station so I apologize in advance if your call is not immediately answered.
VY 73,
Richard Dillman
Chief Operator, MRHS
Once again this Saturday the KSM Transmitter Department plans to exercise the 12Mc RTTY transmitter beginning at about 2000Z and ending at about 2300Z. Press and weather will be broadcast in Baudot and FEC modes.
The Baudot transmission will be 170cps shift, 45.45 baud. The frequency is 12631.0kc.
The tubes currently in the transmitter limit power output to 2.5kW. Once these are replaced a power output of 4 to 5kW will be used. The antenna is a H over 2.
The transmitter for our 8Mc RTTY frequency is undergoing restoration by the Transmitter Department. Once this transmitter operational both 8Mc and 12Mc will be active each Saturday with press and weather information of interest to the maritime community. The 8Mc frequency is 8433.0kc. A double extended Zepp will be used on this frequency.
KSM will be active on Morse as usual on:
426
500
4350.5
6474.0
8438.3
12993.0
16914.0
K6KPH will guard 7050kc and 14050kc for signal reports, NTS traffic and general calls. Since the above frequencies are in a scanner along with the ship calling frequencies, the best procedure to use when calling K6KPH is the same as that for commercial operations: Keep sending "K6KPH" on the above frequencies (within the limits of FCC identification requirements of course). When your call is heard K6KPH will send "DE" after which you can send your call sign. Sometimes things get busy at the station so I apologize in advance if your call is not immediately answered.
VY 73,
Richard Dillman
Chief Operator, MRHS
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