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Bell 202
The Bell 202 modem was an early (1976) modem standard developed by the Bell System. It specifies audio frequency-shift keying (AFSK) to encode and transfer data at a rate of 1200 bits per second, half-duplex. It has separate sets of circuits for 1200 bps and 300 bps rates. These signalling protocols, also used in third-party modems, are referred to generically as ''Bell 202 modulation'', and any device employing it as ''Bell-202-compatible''. * Bell 202 AFSK uses a 1200 Hz tone for ''mark'' (typically a binary ''1'') and 2200 Hz for ''space'' (typically a binary ''0''). In North America, Bell 202 AFSK modulation is used to transmit Caller ID information over POTS lines in the public telephone network. It is also employed in some commercial settings. In addition, Bell 202 is the basis for the most commonly used physical layer for the HART Communication Protocol - a communication protocol widely used in the process industries. Surplus Bell 202 modems were used by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modem
A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by Modulation#Digital modulation methods, modulating one or more carrier wave signals to encode digital information, while the receiver Demodulation, demodulates the signal to recreate the original digital information. The goal is to produce a Signal (electronics), signal that can be transmitted easily and decoded reliably. Modems can be used with almost any means of transmitting analog signals, from light-emitting diodes to radio. Early modems were devices that used audible sounds suitable for transmission over traditional telephone systems and leased lines. These generally operated at 110 or 300 bits per second (bit/s), and the connection between devices was normally manual, using an attached telephone handset. By the 1970s, higher speeds of 1,200 and 2,400 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Amateur Radio
Amateur radio, also known as ham radio, is the use of the radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communications. The term "amateur" is used to specify "a duly authorised person interested in radioelectric practice with a purely personal aim and without pecuniary interest;" (either direct monetary or other similar reward) and to differentiate it from commercial broadcasting, public safety (such as police and fire), or professional two-way radio services (such as maritime, aviation, taxis, etc.). The amateur radio service (''amateur service'' and '' amateur-satellite service'') is established by the International Telecommunication Union (ITU) through the Radio Regulations. National governments regulate technical and operational characteristics of transmissions and issue individual station licenses with a unique identifying call sign, which ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Manchester Code
In telecommunication and data storage, Manchester code (also known as phase encoding, or PE) is a line code in which the encoding of each data bit is either low then high, or high then low, for equal time. It is a self-clocking signal with no DC component. Consequently, electrical connections using a Manchester code are easily galvanically isolated. Manchester code derives its name from its development at the University of Manchester, where the coding was used for storing data on the magnetic drums of the Manchester Mark 1 computer. Manchester code was widely used for magnetic recording on 1600 bpi computer tapes before the introduction of 6250 bpi tapes which used the more efficient group-coded recording. Manchester code was used in early Ethernet physical layer standards and is still used in consumer IR protocols, RFID and near-field communication. Features Manchester coding is a special case of binary phase-shift keying (BPSK), where the data controls the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Production Control System
Within supply chain management and manufacturing, production control is the activity of monitoring and controlling any particular production or operation. Production control is often run from a specific control room or operations room. With inventory control and quality control, production control is one of the key functions of operations management. Overview Production control is the activity of monitoring and controlling a large physical facility or physically dispersed service. It is a "set of actions and decision taken during production to regulate output and obtain reasonable assurance that the specification will be met."S. N. Ghosh (ed.) ''Cement and Concrete Science & Technology.'' 1991. p. 419 The American Production and Inventory Control Society, nowadays APICS, defined production control in 1959 as: :''Production control is the task of predicting, planning and scheduling work, taking into account manpower, materials availability and other capacity restrictions, and co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bell 103 Modem
The Bell 103 modem or Bell 103 dataset was the second commercial modem for computers, released by AT&T Corporation in 1962. It allowed digital data to be transmitted over regular unconditioned telephone lines at a speed of 300 bits per second. It followed the introduction of the 110 baud Bell 101 dataset in 1958. The Bell 103 modem used audio frequency-shift keying to encode data. Different pairs of audio frequencies were used by each station: * The originating station used a mark tone of 1,270 Hz and a space tone of 1,070 Hz. * The answering station used a mark tone of 2,225 Hz and a space tone of 2,025 Hz. Although original Bell 103 modems are no longer in common use, this encoding scheme is referred to generically as "Bell 103 modulation", and any device employing it as "Bell 103-compatible" or "a Bell 103 modem". For many years, higher-speed modems retained the ability to emulate the Bell 103, allowing a fallback method for data to be communicated at low sp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
High Frequency
High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters (ten to one hundred meters). Frequencies immediately below HF are denoted medium frequency (MF), while the next band of higher frequencies is known as the very high frequency (VHF) band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio. Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as "skip" or " skywave" propagation – these frequencies are suitable for long-distance communication across intercontinental distances and for mountainous terrains which prevent line-of-sight communications. The band is used by international shortwave broadcasting station ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Automatic Packet Reporting System
Automatic Packet Reporting System (APRS) is an amateur radio-based system for real time digital communications of information of immediate value in the local area. Data can include object Global Positioning System (GPS) coordinates, weather station telemetry, text messages, announcements, queries, and other telemetry. APRS data can be displayed on a map, which can show stations, objects, tracks of moving objects, weather stations, search and rescue data, and direction finding data. APRS data is typically transmitted on a single shared frequency (depending on country) to be repeated locally by area relay stations (digipeaters) for widespread local consumption. In addition, all such data are typically ingested into the APRS Internet System (APRS-IS) via an Internet-connected receiver (IGate) and distributed globally for ubiquitous and immediate access. Data shared via radio or Internet are collected by all users and can be combined with external map data to build a shared live v ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Very High Frequency
Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves ( radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one meter. Frequencies immediately below VHF are denoted high frequency (HF), and the next higher frequencies are known as ultra high frequency (UHF). VHF radio waves propagate mainly by line-of-sight, so they are blocked by hills and mountains, although due to refraction they can travel somewhat beyond the visual horizon out to about 160 km (100 miles). Common uses for radio waves in the VHF band are Digital Audio Broadcasting (DAB) and FM radio broadcasting, television broadcasting, two-way land mobile radio systems (emergency, business, private use and military), long range data communication up to several tens of kilometers with radio modems, amateur radio, and marine communications. Air traffic control communications and air navigation systems (e.g. VOR and ILS ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Signaling Rate
In telecommunication, data signaling rate (DSR), also known as gross bit rate, is the aggregate rate at which data passes a point in the transmission path of a data transmission system. # The DSR is usually expressed in bits per second. # The data signaling rate is given by \sum_^ \frac where ''m'' is the number of parallel channels, ''ni'' is the number of significant conditions of the modulation in the ''i''-th channel, and ''Ti'' is the unit interval, expressed in seconds, for the ''i''-th channel. # For serial transmission in a single channel, the DSR reduces to (1/''T'')log2''n''; with a two-condition modulation, i. e. ''n'' = 2, the DSR is 1/''T'', according to Hartley's law. # For parallel transmission with equal unit intervals and equal numbers of significant conditions on each channel, the DSR is (''m''/''T'')log2''n''; in the case of a two-condition modulation, this reduces to ''m''/''T''. # The DSR may be expressed in bauds, in which case, the factor log2''ni'' in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Packet Radio
In digital radio, packet radio is the application of packet switching techniques to digital radio communications. Packet radio uses a packet switching protocol as opposed to circuit switching or message switching protocols to transmit digital data via a radio communication link. Packet radio can be differentiated from other digital radio switching schemes by the following attributes: * Transmitted data is broken into packets, each of which contains a destination (and typically the source) address * A transmitted message may be broken into a sequence of packets before transmission, which are then re-assembled into the original message upon reception * Packets for multiple destinations can be transmitted on the same radio link in an asynchronous fashion * A packet may be addressed to all possible recipients rather than a specific one (broadcast) * A packet may be stored and subsequently forwarded towards its destination by a network node This is very similar to how packets of d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Process Manufacturing
Process manufacturing is a branch of manufacturing that is associated with formulas and manufacturing recipes,Difference Between Discrete and Process Manufacturing BatchMaster Blog. and can be contrasted with discrete manufacturing, which is concerned with discrete units, bills of materials and the assembly of components. Process manufacturing is also referred to as a 'process industry' which is defined as an industry, such as the chemical or petrochemical industry, that is concerned with the processing of bulk resources into other products. Process manufacturing is common [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bell System
The Bell System was a system of telecommunication companies, led by the Bell Telephone Company and later by the American Telephone and Telegraph Company (AT&T), that dominated the telephone services industry in North America for over one hundred years from its creation in 1877 until its antitrust breakup in 1983. The system of companies was often colloquially called Ma Bell (as in "Mother Bell"), as it held a vertical monopoly over telecommunication products and services in most areas of the United States and Canada. At the time of the breakup of the Bell System in the early 1980s, it had assets of $150 billion (equivalent to $ billion in ) and employed over one million people. Ever since the 1910s, American antitrust regulators had been observing and accusing the Bell System of abusing its monopoly power, and had brought legal action multiple times over the decades, until in 1974 the Antitrust Division of the U.S. Department of Justice brought a lawsuit against Be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
