The concept uses frequency shifting to overcome the narrowbandwidth of regular telephone systems. The input signal is sent on one telephone line as-is, or in some cases upshifted to provide extra low-frequency response, and sent on a second line shifted down by 3 kHz, which is normally the upper bandpass limit in telephony. Thus, an audio frequency of 5kHz is sent at 2kHz. A receiver on the other end then shifts the second line back up and mixes it with the first. This results in greatly improved audio, adding a full octave of range, and pushing the total bandpass to 6kHz. The sound is then acceptable for voice, if not for music.
It is also possible to add other lines, each increasing the bandpass by another 3kHz. However, the law of diminishing returns takes over, because each successive octave is double the size of the last. A third line pushes the bandpass up 50% to 9kHz, equivalent to AM radio. A fourth line would push it up 33% to 12kHz. FM radio quality would require five telephone lines to be installed, pushing the bandpass up 25% to 15kHz. The audio is shifted down by 6,9, and 12kHz respectively for each additional line.
Frequency extenders have been nearly eliminated by POTS codecs.
NTSC is the first American standard for analog television, published in 1941. In 1961, it was assigned the designation System M. It is also known as EIA standard 170.
A superheterodyne receiver, often shortened to superhet, is a type of radio receiver that uses frequency mixing to convert a received signal to a fixed intermediate frequency (IF) which can be more conveniently processed than the original carrier frequency. It was invented by French radio engineer and radio manufacturer Lucien Lévy. Virtually all modern radio receivers use the superheterodyne principle.
Digital subscriber line is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line (ADSL), the most commonly installed DSL technology, for Internet access.
Slow-scan television (SSTV) is a picture transmission method, used mainly by amateur radio operators, to transmit and receive static pictures via radio in monochrome or color.
In communications and electronic engineering, an intermediate frequency (IF) is a frequency to which a carrier wave is shifted as an intermediate step in transmission or reception. The intermediate frequency is created by mixing the carrier signal with a local oscillator signal in a process called heterodyning, resulting in a signal at the difference or beat frequency. Intermediate frequencies are used in superheterodyne radio receivers, in which an incoming signal is shifted to an IF for amplification before final detection is done.
AM broadcasting is radio broadcasting using amplitude modulation (AM) transmissions. It was the first method developed for making audio radio transmissions, and is still used worldwide, primarily for medium wave transmissions, but also on the longwave and shortwave radio bands.
A blue box is an electronic device that produces tones used to generate the in-band signaling tones formerly used within the North American long-distance telephone network to send line status and called number information over voice circuits. This allowed an illicit user, referred to as a "phreaker", to place long-distance calls, without using the network's user facilities, that would be billed to another number or dismissed entirely as an incomplete call. A number of similar "color boxes" were also created to control other aspects of the phone network.
Power-line communication (PLC) is the carrying of data on a conductor that is also used simultaneously for AC electric power transmission or electric power distribution to consumers. The line that does so is known as a power-line carrier.
Multichannel Television Sound (MTS) is the method of encoding three additional audio channels into analog 4.5 MHz audio carriers on System M and System N. It was developed by the Broadcast Television Systems Committee, an industry group, and sometimes known as BTSC as a result.
In telecommunications, Continuous Tone-Coded Squelch System or CTCSS is one type of in-band signaling that is used to reduce the annoyance of listening to other users on a shared two-way radio communication channel. It is sometimes referred to as tone squelch or PL for Private Line, a trademark of Motorola. It does this by adding a low frequency audio tone to the voice. Where more than one group of users is on the same radio frequency, CTCSS circuitry mutes those users who are using a different CTCSS tone or no CTCSS.
WWV is a shortwave radio station, located near Fort Collins, Colorado. It has broadcast a continuous time signal since 1945, and implements United States government frequency standards, with transmitters operating on 2.5, 5, 10, 15, and 20 MHz. WWV is operated by the U.S. National Institute of Standards and Technology (NIST), under the oversight of its Time and Frequency Division, which is part of NIST's Physical Measurement Laboratory based in Gaithersburg, Maryland.
In analog telephony, a telephone hybrid is the component at the ends of a subscriber line of the public switched telephone network (PSTN) that converts between two-wire and four-wire forms of bidirectional audio paths. When used in broadcast facilities to enable the airing of telephone callers, the broadcast-quality telephone hybrid is known as a broadcast telephone hybrid or telephone balance unit.
In broadcast engineering, a remote broadcast is broadcasting done from a location away from a formal television or radio studio and is considered an electronic field production (EFP). A remote pickup unit (RPU) is usually used to transmit the audio and/or video back to the broadcast station, where it joins the normal airchain. Other methods include satellite trucks, production trucks and even regular telephone lines if necessary.
ITU-R 468 is a standard relating to noise measurement, widely used when measuring noise in audio systems. The standard, now referred to as ITU-R BS.468-4, defines a weighting filter curve, together with a quasi-peak rectifier having special characteristics as defined by specified tone-burst tests. It is currently maintained by the International Telecommunication Union who took it over from the CCIR.
Phonevision was a project by Zenith Radio Company to create the world's first pay television system. It was developed and first launched in Chicago, followed by further trials in New York City and Hartford, Connecticut.
CCIR System B was the 625-line VHF analog broadcast television system which at its peak was adopted by more than one hundred countries, either with PAL or SECAM colour. It is usually associated with CCIR System G for UHF broadcasts.
Equalization, or simply EQ, in sound recording and reproduction is the process of adjusting the volume of different frequency bands within an audio signal. The circuit or equipment used to achieve this is called an equalizer.
CCIR System I is an analogue broadcast television system. It was first used in the Republic of Ireland starting in December 1961 as the 625-line broadcasting standard to be used on VHF Band I and Band III, sharing Band III with 405-line System A signals radiated in the north and east of the country. The Republic of Ireland has (slowly) extended its use of System I onto the UHF bands.
Comrex is an American corporation that designs and manufactures equipment for radio and television broadcasting.
The British Army's Wireless Set, Number 10, was the world's first microwave relay telephone system. It transmitted eight full-duplex (two-way) telephone channels between two stations limited only by the line-of-sight, often on the order of 25 to 50 miles. The stations were mounted in highly mobile trailers and were set up simply by aiming the two parabolic antennas on the roof at the next station.
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