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Milliwatt Test
A Milliwatt test (Milliwatt line) is a test method or test facility used in telecommunications to measure line quality and transmission loss between stations or points in an analog telephone system. The test consists of transmitting an analog sinusoidal signal at the frequency of 1004 Hz with the power level of 0 (zero) dBm. By definition, this is the equivalent of a continuous power dissipation of 1 mW (milliWatt), i.e., the power consumed if a voltage of 0.775 V( RMS) is applied to a telephone line with 600 Ohm nominal impedance.H.A. Quinn, et al., 'A New Standard Volume Indicator and Reference Level', Proceedings of the Institute of Radio Engineers, Volume 28 (1940) In the Bell System, central offices provided this type of service on a dedicated telephone number (102 type Milliwatt line) for remote subscriber line testing. In conjunction, a second line (type 100 line) provided quiet termination. Various types of test lines were called "100", "102", "104" etc., because thes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telecommunications
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that feasible with the human voice, but with a similar scale of expediency; thus, slow systems (such as postal mail) are excluded from the field. The transmission media in telecommunication have evolved through numerous stages of technology, from beacons and other visual signals (such as smoke signals, semaphore telegraphs, signal flags, and optical heliographs), to electrical cable and electromagnetic radiation, including light. Such transmission paths are often divided into communication channels, which afford the advantages of multiplexing multiple concurrent communication sessions. ''Telecommunication'' is often used in its plural form. Other examples of pre-modern long-distance communication included audio messages, such as coded drumb ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hertz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one hertz is the reciprocal of one second. It is named after Heinrich Rudolf Hertz (1857–1894), the first person to provide conclusive proof of the existence of electromagnetic waves. Hertz are commonly expressed in multiples: kilohertz (kHz), megahertz (MHz), gigahertz (GHz), terahertz (THz). Some of the unit's most common uses are in the description of periodic waveforms and musical tones, particularly those used in radio- and audio-related applications. It is also used to describe the clock speeds at which computers and other electronics are driven. The units are sometimes also used as a representation of the energy of a photon, via the Planck relation ''E'' = ''hν'', where ''E'' is the photon's energy, ''ν'' is its freq ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Watt
The watt (symbol: W) is the unit of power or radiant flux in the International System of Units (SI), equal to 1 joule per second or 1 kg⋅m2⋅s−3. It is used to quantify the rate of energy transfer. The watt is named after James Watt (1736–1819), an 18th-century Scottish inventor, mechanical engineer, and chemist who improved the Newcomen engine with his own steam engine in 1776. Watt's invention was fundamental for the Industrial Revolution. Overview When an object's velocity is held constant at one metre per second against a constant opposing force of one newton, the rate at which work is done is one watt. : \mathrm In terms of electromagnetism, one watt is the rate at which electrical work is performed when a current of one ampere (A) flows across an electrical potential difference of one volt (V), meaning the watt is equivalent to the volt-ampere (the latter unit, however, is used for a different quantity from the real power of an electrical circuit). : ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Volt
The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827). Definition One volt is defined as the electric potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points. Equivalently, it is the potential difference between two points that will impart one joule of energy per coulomb of charge that passes through it. It can be expressed in terms of SI base units ( m, kg, second, s, and ampere, A) as : \text = \frac = \frac = \frac. It can also be expressed as amperes times ohms (current times resistance, Ohm's law), webers per second (magnetic flux per time), watts per ampere (power per current), or joules per coulomb (energy per charge), which is also equivalent to electronvolts per elementary charge: : \text = \tex ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Root Mean Square
In mathematics and its applications, the root mean square of a set of numbers x_i (abbreviated as RMS, or rms and denoted in formulas as either x_\mathrm or \mathrm_x) is defined as the square root of the mean square (the arithmetic mean of the squares) of the set. The RMS is also known as the quadratic mean (denoted M_2) and is a particular case of the generalized mean. The RMS of a continuously varying function (denoted f_\mathrm) can be defined in terms of an integral of the squares of the instantaneous values during a cycle. For alternating electric current, RMS is equal to the value of the constant direct current that would produce the same power dissipation in a resistive load. In estimation theory, the root-mean-square deviation of an estimator is a measure of the imperfection of the fit of the estimator to the data. Definition The RMS value of a set of values (or a continuous-time waveform) is the square root of the arithmetic mean of the squares of the values, or th ... [...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] |
Tandem Office
A class-4, or tandem, telephone switch is a U.S. telephone company central office telephone exchange used to interconnect local exchange carrier offices for long distance communications in the public switched telephone network. A class-4 switch does not connect directly to telephones; instead, it connects to other class-4 switches and to class-5 telephone switches. The telephones of service subscribers are wired to class-5 switches. When a call is placed to a telephone that is not on the same class-5 switch as the originating subscriber, the call may be routed through one or more class-4 switches to reach its destination. Etymology ''Tandem'' derives from the Latin adverb ''tandem'' meaning ''at length'', and is used in English to mean a group of two people or machines working together, usually in series. A tandem switch is used to interconnect other switches via trunks. Thus, tandem switches are always part of a series of switches and lines that connect telephone callers t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Milliwatt
In digital telephony, the digital milliwatt is a standard test signal that serves as a reference for analog signal levels in the telecommunications network.Anttalainen T., ''Introduction to Telecommunications Network Engineering, Artech House (2003). When decoding the digital milliwatt, a PCM decoder produces a sinusoidal signal with a frequency of with one milliwatt in power (). The digital milliwatt signal is encoded by eight 8-bit words corresponding to one pulse-code modulated cycle of the signal, sampled 8000 times per second. It is typically stored in read-only memory (ROM) in the telecommunication equipment.AT&T, ''Digital Channel Bank Requirements And Objectives'', Publication No. 43801 (December 1978). page A6. The digital milliwatt signal is often generated in instruments in place of separate test equipment. It has the advantage of being tied in frequency and amplitude to the relatively stable digital clock signal and power (voltage) supply, respectively, that are us ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Loop Around
A loop line or loop around is a telephone company test circuit. The circuit has two associated phone numbers. When one side of the loop is called (side A), the caller receives a test tone of approximately 1000 Hz (milliwatt test). When the second number (side B) is called, it produces dead silence, but the party on side A hears the milliwatt test tone drop, and is connected to the person on side B. The purpose of the loop around test is to allow circuit testing to a distant central office without needing a person at the far end. The technician can send a tone down either line and measure the response tone on the second line to determine the path loss parameters. When a line is connected to side A, multiple telephone lines, within limits, may connect to side B and thus be connected into a conference with the person on side A. The function of the tone on side A was to alert those already connected, when somebody called the B side and connected. Teenagers discovered that the te ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plant Test Number
In telecommunications, a plant test number is a telephone number reserved for use by telephone installers or other workers to test an individual telephone line. Test number are typically unlisted. The North American Numbering Plan (NANP) reserves the exchange (''central office'') prefixes ''958'' and ''959'' for plant testing.''Telcordia Notes on the Network'', Telcordia Technologies, Special Report SR-2275 Issue 4 (October 2000), Section 8.2.5, p.8-8 Central office code 958 is intended for communications between switching centers. Central office code 959 with three or four additional digits is dedicated for access to office test lines in local exchange carrier (LEC) and interoffice carrier (IC) central offices. The specifications define several test features for line conditions, such as quiet line and busy line, and test tones transmitted to callers. The tests available for plant testing include * Automatic number announcement circuit, a machine which announces the caller's number ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transmission Level Point
In telecommunication, a transmission level point (TLP) is a physical test point in an electronic circuit, typically a transmission channel, where a test signal may be inserted or measured.Whitham R. Reeve (1992) ''Subscriber Loop Signaling and Transmission Handbook—Analog'', IEEE Press, p.229 Typically, various parameters, such as the power of the signal, noise, or test tones inserted are specified or measured at the TLP. The nominal transmission level at a TLP is a function of system design and is an expression of the design gain or attenuation (loss). Voice-channel transmission levels at test points are measured in decibel-milliwatts (dBm) at a frequency of ca. 1000 hertz. The dBm is an absolute level with respect to 1 mW. The TLP is thus characterized by the relation: :TLP = dBm — dBm0 When the nominal signal power is 0dBm at the TLP, the test point is called a ''zero transmission level point'', or ''zero-dBm TLP''. In general, the term ''TLP'' is commonly used as if ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telecommunications Systems
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that feasible with the human voice, but with a similar scale of expediency; thus, slow systems (such as postal mail) are excluded from the field. The transmission media in telecommunication have evolved through numerous stages of technology, from beacons and other visual signals (such as smoke signals, semaphore telegraphs, signal flags, and optical heliographs), to electrical cable and electromagnetic radiation, including light. Such transmission paths are often divided into communication channels, which afford the advantages of multiplexing multiple concurrent communication sessions. ''Telecommunication'' is often used in its plural form. Other examples of pre-modern long-distance communication included audio messages, such as coded drumbea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
