Электр сигналдармен жазылған хабарларды жіберу құрылғысы

Device for transmitting messages in written form by electrical signals

the telecommunications system consisting of teleprinters connected by radio

A teleprinter (teletypewriter, teletype or TTY) is an electromechanical device that can be used to send and receive typed messages through various communications channels, in both point to point and point to multipoint configurations. Initially, from 1887 at the earliest, teleprinters were used in telegraphy. Electrical telegraphy had been developed decades earlier in the late 1830s and 1840s, then using simpler Morse key equipment and telegraph operators. The introduction of teleprinters automated much of this work and eventually largely replaced skilled operators versed in Morse code with typists and machines communicating faster via Baudot code. With the development of early computers in the 1950s, teleprinters were adapted to allow typed data to be sent to a computer, and responses printed. Some teleprinter models could also be used to create punched tape for data storage (either from typed input or from data received from a remote source) and to read back such tape for local printing or transmission. A teleprinter attached to a modem could also communicate through telephone lines. This latter configuration was often used to connect teleprinters to remote computers, particularly in time sharing environments. Teleprinters have largely been replaced by fully electronic computer terminals which typically have a computer monitor instead of a printer (though the term "TTY" is still occasionally used to refer to them, such as in Unix systems). Teleprinters are still widely used in the aviation industry (see AFTN and airline teletype system), and variants called Telecommunications Devices for the Deaf (TDDs) are used by the hearing impaired for typed communications over ordinary telephone lines.

The teleprinter evolved through a series of inventions by a number of engineers, including Samuel Morse, Alexander Bain, Royal Earl House, David Edward Hughes, Emile Baudot, Donald Murray, Charles L. Krum, Edward Kleinschmidt and Frederick G. Creed. Teleprinters were invented in order to send and receive messages without the need for operators trained in the use of Morse code. A system of two teleprinters, with one operator trained to use a keyboard, replaced two trained Morse code operators. The teleprinter system improved message speed and delivery time, making it possible for messages to be flashed across a country with little manual intervention. There were a number of parallel developments on both sides of the Atlantic Ocean. In 1835 Samuel Morse devised a recording telegraph, and Morse code was born. Morse's instrument used a current to displace the armature of an electromagnet, which moved a marker, therefore recording the breaks in the current. Cooke & Wheatstone received a British patent covering telegraphy in 1837 and a second one in 1840 which described a type printing telegraph with steel type fixed at the tips of petals of a rotating brass daisy wheel, struck by an "electric hammer" to print Roman letters through carbon paper onto a moving paper tape. In 1841 Alexander Bain devised an electromagnetic printing telegraph machine. It used pulses of electricity created by rotating a dial over contact points to release and stop a type wheel turned by weight driven clockwork; a second clockwork mechanism rotated a drum covered with a sheet of paper and moved it slowly upwards so that the type wheel printed its signals in a spiral. The critical issue was to have the sending and receiving elements working synchronously. Bain attempted to achieve this using centrifugal governors to closely regulate the speed of the clockwork. It was patented, along with other devices, on April 21, 1841. By 1846, the Morse telegraph service was operational between Washington, D. C., and New York. Royal Earl House patented his printing telegraph that same year. He linked two 28 key piano style keyboards by wire. Each piano key represented a letter of the alphabet and when pressed caused the corresponding letter to print at the receiving end. A "shift" key gave each main key two optional values. A 56 character typewheel at the sending end was synchronised to coincide with a similar wheel at the receiving end. If the key corresponding to a particular character was pressed at the home station, it actuated the typewheel at the distant station just as the same character moved into the printing position, in a way similar to the (much later) daisy wheel printer. It was thus an example of a synchronous data transmission system. House's equipment could transmit around 40 instantly readable words per minute, but was difficult to manufacture in bulk. The printer could copy and print out up to 2,000 words per hour. This invention was first put in operation and exhibited at the Mechanics Institute in New York in 1844. Landline teleprinter operations began in 1849, when a circuit was put in service between Philadelphia and New York City. In 1855, David Edward Hughes introduced an improved machine built on the work of Royal Earl House. In less than two years, a number of small telegraph companies, including Western Union in early stages of development, united to form one large corporation – Western Union Telegraph Co. – to carry on the business of telegraphy on the Hughes system. In France, Émile Baudot designed in 1874 a system using a five unit code, which began to be used extensively in that country from 1877. The British Post Office adopted the Baudot system for use on a simplex circuit between London and Paris in 1897, and subsequently made considerable use of duplex Baudot systems on their Inland Telegraph Services. During 1901, Baudot's code was modified by Donald Murray (1865–1945, originally from New Zealand), prompted by his development of a typewriter like keyboard. The Murray system employed an intermediate step, a keyboard perforator, which allowed an operator to punch a paper tape, and a tape transmitter for sending the message from the punched tape. At the receiving end of the line, a printing mechanism would print on a paper tape, and/or a reperforator could be used to make a perforated copy of the message. As there was no longer a direct correlation between the operator's hand movement and the bits transmitted, there was no concern about arranging the code to minimize operator fatigue, and instead Murray designed the code to minimize wear on the machinery, assigning the code combinations with the fewest punched holes to the most frequently used characters. The Murray code also introduced what became known as "format effectors" or "control characters" – the CR (Carriage Return) and LF (Line Feed) codes. A few of Baudot's codes moved to the positions where they have stayed ever since: the NULL or BLANK and the DEL code. NULL/BLANK was used as an idle code for when no messages were being sent. In 1904, Krum filed a patent for a 'type wheel printing telegraph machine' which was issued in August, 1907. In 1906 Charles Krum's son, Howard Krum, joined his father in this work. It was Howard who developed and patented the start stop synchronizing method for code telegraph systems, which made possible the practical teleprinter. In 1908, a working teleprinter was produced by the Morkrum Company (formed between Joy Morton and Charles Krum), called the Morkrum Printing Telegraph, which was field tested with the Alton Railroad. In 1910, the Morkrum Company designed and installed the first commercial teletypewriter system on Postal Telegraph Company lines between Boston and New York City using the "Blue Code Version" of the Morkrum Printing Telegraph. In 1916, Edward Kleinschmidt filed a patent application for a typebar page printer. In 1919, shortly after the Morkrum company obtained their patent for a start stop synchronizing method for code telegraph systems, which made possible the practical teleprinter, Kleinschmidt filed an application titled "Method of and Apparatus for Operating Printing Telegraphs" which included an improved start stop method. The basic start stop procedure, however, is much older than the Kleinschmidt and Morkrum inventions. It was already proposed by D'Arlincourt in 1870. Instead of wasting time and money in patent disputes on the start stop method, Kleinschmidt and the Morkrum Company decided to merge and form the Morkrum Kleinschmidt Company in 1924. The new company combined the best features of both their machines into a new typewheel printer for which Kleinschmidt, Howard Krum, and Sterling Morton jointly obtained a patent. By 1938, the teleprinter network, handling weather traffic, extended over 20,000 miles, covering all 48 states except Maine, New Hampshire, and South Dakota.

Most teleprinters used the 5 bit International Telegraph Alphabet No. 2 (ITA2). This was limited to 32 codes (25 = 32). One had to use "FIGS" (for "figures") and "LTRS" (for "letters") keys to shift state, for a combined character set sufficient to type both letters and numbers, as well as some special characters. (The letters were uppercase only.) Special versions of teleprinters had FIGS characters for specific applications, such as weather symbols for weather reports. Print quality was poor by modern standards. The ITA2 code was used asynchronously with start and stop bits: the asynchronous code design was intimately linked with the start stop electro mechanical design of teleprinters. (Early systems had used synchronous codes, but were hard to synchronize mechanically). Other codes, such as FIELDATA and Flexowriter, were introduced but never became as popular as ITA2. Mark and space are terms describing logic levels in teleprinter circuits. The native mode of communication for a teleprinter is a simple series DC circuit that is interrupted, much as a rotary dial interrupts a telephone signal. The marking condition is when the circuit is closed (current is flowing), the spacing condition is when the circuit is open (no current is flowing). The "idle" condition of the circuit is a continuous marking state, with the start of a character signalled by a "start bit", which is always a space. Following the start bit, the character is represented by a fixed number of bits, such as 5 bits in the ITA2 code, each either a mark or a space to denote the specific character or machine function. After the character's bits, the sending machine sends one or more stop bits. The stop bits are marking, so as to be distinct from the subsequent start bit. If the sender has nothing more to send, the line simply remains in the marking state (as if a continuing series of stop bits) until a later space denotes the start of the next character. The time between characters need not be an integral multiple of a bit time, but it must be at least the minimum number of stop bits required by the receiving machine. When the line is broken, the continuous spacing (open circuit, no current flowing) causes a receiving teleprinter to cycle continuously, even in the absence of stop bits. It prints nothing because the characters received are all zeros, the ITA2 blank (or ASCII) null character. Teleprinter circuits were generally leased from a communications common carrier and consisted of ordinary telephone cables that extended from the teleprinter located at the customer location to the common carrier central office. These teleprinter circuits were connected to switching equipment at the central office for Telex and TWX service. Private line teleprinter circuits were not directly connected to switching equipment. Instead, these private line circuits were connected to network hubs and repeaters configured to provide point to point or point to multipoint service. More than two teleprinters could be connected to the same wire circuit by means of a current loop. Earlier teleprinters had three rows of keys and only supported upper case letters. They used the 5 bit ITA2 code and generally worked at 60 to 100 words per minute. Later teleprinters, specifically the Teletype Model 33, used ASCII code, an innovation that came into widespread use in the 1960s as computers became more widely available. "Speed", intended to be roughly comparable to words per minute, is the standard term introduced by Western Union for a mechanical teleprinter data transmission rate using the 5 bit ITA2 code that was popular in the 1940s and for several decades thereafter. Such a machine would send 1 start bit, 5 data bits, and 1.42 stop bits. This unusual stop bit time is actually a rest period to allow the mechanical printing mechanism to synchronize in the event that a garbled signal is received. This is true especially on high frequency radio circuits where selective fading is present. Selective fading causes the mark signal amplitude to be randomly different from the space signal amplitude. Selective fading, or Rayleigh fading can cause two carriers to randomly and independently fade to different depths. Since modern computer equipment cannot easily generate 1.42 bits for the stop period, common practice is to either approximate this with 1.5 bits, or to send 2.0 bits while accepting 1.0 bits receiving. For example, a "60 speed" machine is geared at 45.5 baud (22.0 ms per bit), a "66 speed" machine is geared at 50.0 baud (20.0 ms per bit), a "75 speed" machine is geared at 56.9 baud (17.5 ms per bit), a "100 speed" machine is geared at 74.2 baud (13.5 ms per bit), and a "133 speed" machine is geared at 100.0 baud (10.0 ms per bit). 60 speed became the de facto standard for amateur radio RTTY operation because of the widespread availability of equipment at that speed and the U. S. Federal Communications Commission (FCC) restrictions to only 60 speed from 1953 to 1972. Telex, news agency wires and similar services commonly used 66 speed services. There was some migration to 75 and 100 speed as more reliable devices were introduced. However, the limitations of HF transmission such as excessive error rates due to multipath distortion and the nature of ionospheric propagation kept many users at 60 and 66 speed. Most audio recordings in existence today are of teleprinters operating at 60 words per minute, and mostly of the Teletype Model 15. Another measure of the speed of a teletypewriter was in total "operations per minute (OPM)". For example, 60 speed was usually 368 OPM, 66 speed was 404 OPM, 75 speed was 460 OPM, and 100 speed was 600 OPM. Western Union Telexes were usually set at 390 OPM, with 7.0 total bits instead of the customary 7.42 bits. Both wire service and private teleprinters had bells to signal important incoming messages and could ring 24/7 while the power was turned on. For example, ringing 4 bells on UPI wire service machines meant an "Urgent" message; 5 bells was a "Bulletin"; and 10 bells was a FLASH, used only for very important news. The teleprinter circuit was often linked to a 5 bit paper tape punch (or "reperforator") and reader, allowing messages received to be resent on another circuit. Complex military and commercial communications networks were built using this technology. Message centers had rows of teleprinters and large racks for paper tapes awaiting transmission. Skilled operators could read the priority code from the hole pattern and might even feed a "FLASH PRIORITY" tape into a reader while it was still coming out of the punch. Routine traffic often had to wait hours for relay. Many teleprinters had built in paper tape readers and punches, allowing messages to be saved in machine readable form and edited off line. Communication by radio, known as radioteletype or RTTY (pronounced ritty), was also common, especially among military users. Ships, command posts (mobile, stationary, and even airborne) and logistics units took advantage of the ability of operators to send reliable and accurate information with a minimum of training. Amateur radio operators continue to use this mode of communication today, though most use computer interface sound generators, rather than legacy hardware teleprinter equipment. Numerous modes are in use within the "ham radio" community, from the original ITA2 format to more modern, faster modes, which include error checking of characters.

A typewriter or electromechanical printer can print characters on paper, and execute operations such as move the carriage back to the left margin of the same line (carriage return), advance to the same column of the next line (line feed), and so on. Commands to control non printing operations were transmitted in exactly the same way as printable characters by sending control characters with defined functions (e. g., the line feed character forced the carriage to move to the same position on the next line) to teleprinters. In modern computing and communications a few control characters, such as carriage return and line feed, have retained their original functions (although they are often implemented in software rather than activating electromechanical mechanisms to move a physical printer carriage) but many others are no longer required and are used for other purposes.

Some teleprinters had a "Here is" key, which transmitted a fixed sequence of 20 or 22 characters, programmable by breaking tabs off a drum. This sequence could also be transmitted automatically upon receipt of an ENQ (control E) signal, if enabled. This was commonly used to identify a station; the operator could press the key to send the station identifier to the other end, or the remote station could trigger its transmission by sending the ENQ character, essentially asking "who are you?"

The Gretag ETK 47 teleprinter developed in Switzerland by Edgar Gretener in 1947 uses a 14 bit start stop transmission method similar to the 5 bit code used by other teleprinters. However, instead of a more or less arbitrary mapping between 5 bit codes and letters in the Latin alphabet, all characters (letters, digits, and punctuation) printed by the ETK are built from 14 basic elements on a print head, very similar to the 14 elements on a modern fourteen segment display, each one selected independently by one of the 14 bits during transmission. Because it does not use a fixed character set, but instead builds up characters from smaller elements, the ETK printing element does not require modification to switch between Latin, Cyrillic, and Greek characters.

In 1931, American inventor Edward Kleinschmidt formed Kleinschmidt Labs to pursue a different design of teleprinter. In 1944 Kleinschmidt demonstrated their lightweight unit to the Signal Corps and in 1949 their design was adopted for the Army's portable needs. In 1956, Kleinschmidt Labs merged with Smith Corona, which then merged with the Marchant Calculating Machine Co., forming the SCM Corporation. By 1979, the Kleinschmidt division was turning to Electronic Data Interchange and away from mechanical products. Kleinschmidt machines, with the military as their primary customer, used standard military designations for their machines. The teleprinter was identified with designations such as a TT 4/FG, while communication "sets" to which a teleprinter might be a part generally used the standard Army/Navy designation system such as AN/FGC 25. This includes Kleinschmidt teleprinter TT 117/FG and tape reperforator TT 179/FG.

Morkrum made their first commercial installation of a printing telegraph with the Postal Telegraph Company in Boston and New York in 1910. It became popular with railroads, and the Associated Press adopted it in 1914 for their wire service. Morkrum merged with their competitor Kleinschmidt Electric Company to become Morkrum Kleinschmidt Corporation shortly before being renamed the Teletype Corporation.

Texas Instruments developed its own line of teletypes in 1971, the Silent 700. Their name came from the use of a thermal printer head to emit copy, making them substantially quieter than contemporary teletypes using impact printing, and some such as the 1975 Model 745 and 1983 Model 707 were even small enough to be sold as portable units. Certain models came with acoustic couplers and some had internal storage, initially cassette tape in the 1973 Models 732/733 ASR and later bubble memory in the 1977 Models 763/765, the first and one of the few commercial products to use the technology. In these units their storage capability essentially acted as a form of punched tape. The last Silent 700 was the 1987 700/1200 BPS, which was sold into the early 1990s.

A global teleprinter network called Telex was developed in the late 1920s, and was used through most of the 20th century for business communications. The main difference from a standard teleprinter is that Telex includes a switched routing network, originally based on pulse telephone dialing, which in the United States was provided by Western Union. AT&T developed a competing network called "TWX" which initially also used rotary dialing and Baudot code, carried to the customer premises as pulses of DC on a metallic copper pair. TWX later added a second ASCII based service using Bell 103 type modems served over lines whose physical interface was identical to regular telephone lines. In many cases, the TWX service was provided by the same telephone central office that handled voice calls, using class of service to prevent POTS customers from connecting to TWX customers. Telex is still in use in some countries for certain applications such as shipping, news, weather reporting and military command. Many business applications have moved to the Internet as most countries have discontinued telex/TWX services.

In addition to the 5 bit Baudot code and the much later seven bit ASCII code, there was a six bit code known as the Teletypesetter code (TTS) used by news wire services. It was first demonstrated in 1928 and began to see widespread use in the 1950s. Through the use of "shift in" and "shift out" codes, this six bit code could represent a full set of upper and lower case characters, digits, symbols commonly used in newspapers, and typesetting instructions such as "flush left" or "center", and even "auxiliary font", to switch to italics or bold type, and back to roman ("upper rail"). The TTS produces aligned text, taking into consideration character widths and column width, or line length. A Model 20 Teletype machine with a paper tape punch ("reperforator") was installed at subscriber newspaper sites. Originally these machines would simply punch paper tapes and these tapes could be read by a tape reader attached to a "Teletypesetter operating unit" installed on a Linotype machine. The "operating unit" was essentially a tape reader which actuated a mechanical box, which in turn operated the Linotype's keyboard and other controls, in response to the codes read from the tape, thus creating type for printing in newspapers and magazines. This allowed higher production rates for the Linotype, and was used both locally, where the tape was first punched and then fed to the machine, as well as remotely, using tape transmitters and receivers. Remote use played an essential role for distributing identical content, such as syndicated columns, news agency news, classified advertising, and more, to different publications across wide geographical areas. In later years the incoming 6 bit current loop signal carrying the TTS code was connected to a minicomputer or mainframe for storage, editing, and eventual feed to a phototypesetting machine.

Computers used teleprinters for input and output from the early days of computing. Punched card readers and fast printers replaced teleprinters for most purposes, but teleprinters continued to be used as interactive time sharing terminals until video displays became widely available in the late 1970s. Users typed commands after a prompt character was printed. Printing was unidirectional; if the user wanted to delete what had been typed, further characters were printed to indicate that previous text had been cancelled. When video displays first became available the user interface was initially exactly the same as for an electromechanical printer; expensive and scarce video terminals could be used interchangeably with teleprinters. This was the origin of the text terminal and the command line interface. Paper tape was sometimes used to prepare input for the computer session off line and to capture computer output. The popular Teletype Model 33 used 7 bit ASCII code (with an eighth parity bit) instead of Baudot. The common modem communications settings, Start/Stop Bits and Parity, stem from the Teletype era. In early operating systems such as Digital's RT 11, serial communication lines were often connected to teleprinters and were given device names starting with This and similar conventions were adopted by many other operating systems. Unix and Unix like operating systems use the prefix , for example , or (for pseudo tty), such as , but some of them (e. g. Solaris & recent Linux) have replaced pty files by a pts folder (where "pt" stands for "pseudoterminal" instead). In many computing contexts, "TTY" has become the name for any text terminal, such as an external console device, a user dialing into the system on a modem on a serial port device, a printing or graphical computer terminal on a computer's serial port or the RS 232 port on a USB to RS 232 converter attached to a computer's USB port, or even a terminal emulator application in the window system using a pseudoterminal device. Teleprinters were also used to record fault printout and other information in some TXE telephone exchanges.

Although printing news, messages, and other text at a distance is still universal, the dedicated teleprinter tied to a pair of leased copper wires was made functionally obsolete by the fax, personal computer, inkjet printer, email, and the Internet. In the 1980s, packet radio became the most common form of digital communications used in amateur radio. Soon, advanced multimode electronic interfaces such as the AEA PK 232 were developed, which could send and receive not only packet, but various other modulation types including Baudot. This made it possible for a home or laptop computer to replace teleprinters, saving money, complexity, space and the massive amount of paper which mechanical machines used.