In telecommunications, squelch is a circuit function that acts to suppress the audio (or video) output of a receiver in the absence of a sufficiently strong desired input signal. Telecommunication involves the transmission of signals over a distance for the purpose of communication. ... An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, and switches. ... Sound reproduction is the electrical or mechanical re-creation and/or amplification of sound, often as music. ... Video is the technology of capturing, recording, processing, transmitting, and reconstructing moving pictures, typically using celluloid film, electronic signals, or digital media, primarily for viewing on television or computer monitors. ... // Information processing In information processing, output is the process of transmitting information by an object (verb usage). ... In radio terminology, a receiver is an electronic circuit that receives a radio signal from an antenna and decodes the signal for use as sound, pictures, navigational-position information, etc. ... The term input has a variety of uses in different fields. ... In telecommunication, signalling (or signaling) has the following meanings: The use of signals for controlling communications. ...

Squelch excludes undesired lower-power input signals that may be present at or near the frequency of the desired signal. Squelch is a noise gate that only allows signals at a specified strength over a threshold to be played through the speaker. As an example, general static (with no transmission) is squelched out. (Contrast with noise suppression.)^[1] In physics, power (symbol: P) is the amount of work done per unit of time. ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... A noise gate is an electronic device or software logic that is used to control the volume of an audio signal. ... Active noise control (also known as noise cancellation, active noise reduction (ANR) or antinoise) is a method for reducing unwanted sound. ...

Carrier squelch

A simple carrier squelch or noise squelch operates strictly on the signal strength of the signal, such as when a television mutes the audio or blanks the video on "empty" channels, or when a walkie talkie mutes the audio when no signal is present. In some designs, the squelch threshold is preset. For example, television squelch settings are usually preset. Receivers in base stations at remote mountain top sites are usually not adjustable remotely from the control point. In telecommunications, and particularly in radio, signal strength is the measure of how strongly a transmitted signal is being received, measured, or predicted, at a reference point that is a significant distance from the transmitting antenna. ... In telecommunication, signalling (or signaling) has the following meanings: The use of signals for controlling communications. ... The MUTE Network, MUTE-net for short, is a peer-to-peer and friend-to-friend file sharing network developed with anonymity in mind. ... There are a number of uses for the word blank: Look up blank in Wiktionary, the free dictionary. ... Channel, in communications (sometimes called communications channel), refers to the medium through which information is transmitted from a sender (or transmitter) to a receiver. ... Recreational, toy and amateur radio walkie talkies A walkie-talkie is a portable, bi-directional radio transceiver, first developed for military use. ... Two GSM mobile phone base stations disguised as trees in Dublin, Ireland. ...

In devices such as radiotelephones (also known as two-way radios), the squelch threshold is set with an adjustable knob marked squelch. This setting adjusts the threshold at which signals will open the audio channel. Backing off the control will turn on the audio, and the operator will hear white noise if there is no signal present. The usual operation is to adjust the control until the channel just shuts off - then only a small threshold signal is needed to turn on the speaker. However, if a weak signal is annoying, the operator can adjust the squelch to open only when stronger signals are received. A radiotelephone is a communications device that allows two or more people to talk using radio. ... A two-way radio is simply a radio that can both transmit and receive (a transceiver). ... For other uses of the term white noise, see white noise (disambiguation). ...

A typical FM two-way radio carrier squelch circuit takes out the voice components of the receive audio by passing the detected audio through a high-pass filter. A typical filter might pass frequencies over 2,000 Hz (2 KHz). The squelch control adjusts the gain of an amplifier which varies the level of noise coming out of the filter. The audio output of the filter and amplifier is rectified and produces a DC voltage when noise is present. The presence of noise creates a DC voltage which turns the receiver audio off. When a signal with little or no noise is received, the voltage goes away and the receiver audio turns on. The abbreviations FM, Fm, and fm may refer to: Electrical engineering Frequency modulation (FM) and its most common applications: FM broadcasting, used primarily to broadcast music and speech at VHF frequencies FM synthesis, a sound-generation technique popularized by early digital synthesizers Science Femtometre (fm), an SI measure of length... A two-way radio is simply a radio that can both transmit and receive (a transceiver). ...

Tone squelch and selective calling

Main article: Selective calling

Tone squelch, or other forms of selective calling, are sometimes used to solve interference problems. Where more than one user is on the same channel (co-channel users), selective calling addresses a subset of all receivers. Instead of turning on the receive audio for any signal, the audio turns on only in the presence of the correct selective calling code. This is akin to the use of a lock on a door. A carrier squelch is unlocked and will let any signal in. Selective calling locks out all signals except ones with the correct code. In a conventional, analog two-way radio system, a standard radio has noise squelch or carrier squelch which allows a radio to receive all transmissions on a channel. ...

In non-critical uses, selective calling can also be used to hide the presence of interfering signals such as receiver-produced intermodulation. Receivers with poor specifications — such as scanners or low-cost mobile radios — cannot reject the strong signals present in urban environments. The interference will still be present. It will still degrade system performance but by using selective calling the user will not have to hear the noises produced by receiving the interference.

Four different techniques are commonly used. Selective calling can be regarded as a form of in-band signaling. It has been suggested that this article or section be merged with In-band signalling. ...

CTCSS

Main article: CTCSS

CTCSS (Continuous Tone-Coded Squelch System) continuously superimposes any one of about 50 low-pitch audio tones on the transmitted signal, ranging from 67 to 254 Hz. CTCSS is often called PL tone (for Private Line, a trademark of Motorola), or simply tone squelch. General Electric's implementation of CTCSS is called Channel Guard (or CG). There are many other company-specific names used by radio vendors to describe compatible options. Any CTCSS system that has compatible tones is interchangeable. Old and new radios with CTCSS and radios across manufacturers are compatible. In telecommunications, squelch is a circuit function that acts to suppress the audio (or video) output of a receiver. ... In music, pitch is the psychological correlate of the fundamental frequency of a note. ... The hertz (symbol: Hz) is the SI unit of frequency. ... A trademark or trade mark[1] is a distinctive sign of some kind which is used by a business to uniquely identify itself and its products and services to consumers, and to distinguish the business and its products or services from those of other businesses. ... Motorola (NYSE: MOT) is an American international communications company based in Schaumburg, Illinois, a Chicago suburb. ... GE redirects here. ...

SelCall

Main article: Selcall

Selcall (Selective Calling) transmits a burst of five inband audio tones at the beginning of each transmission. This feature is common in European systems. In the same way that a single CTCSS tone would be used on an entire group of radios, a single five-tone sequence is used in a group of radios. Selcall (selective calling) is a type of squelch protocol used in radio communications systems, in which transmissions are preceded by a brief burst of sequential audio tones. ...

DCS

DCS (Digital-Coded Squelch) superimposes a continuous stream of FSK digital data, at about 131 baud, on the transmitted signal. In the same way that a single CTCSS tone would be used on an entire group of radios, the same DCS code is used in a group of radios. DCS is also referred to as DPL tone (for Digital Private Line, a trademark of Motorola), and likewise, GE's implementation of DCS is referred to a Digital Channel Guard (or DCG). Radios with DCS options are generally compatible provided the radio's encoder-decoder will use the same code as radios in the existing system. A running stream. ... FSK can have alternative meanings; Frequency-shift keying is frequency modulation. ... A digital system is one that uses discrete numbers, especially binary numbers, or non-numeric symbols such as letters or icons, for input, processing, transmission, storage, or display, rather than a continuous spectrum of values (an analog system). ... In general, data consist of propositions that reflect reality. ... In telecommunications and electronics, baud (pronounced , unit symbol Bd) is a measure of the symbol rate, that is the number of distinct symbolic changes (signalling event) made to the transmission medium per second in a digitally modulated signal. ... A trademark or trade mark[1] is a distinctive sign of some kind which is used by a business to uniquely identify itself and its products and services to consumers, and to distinguish the business and its products or services from those of other businesses. ... Motorola (NYSE: MOT) is an American international communications company based in Schaumburg, Illinois, a Chicago suburb. ...

XTCSS

XTCSS is the newest signaling technique and it provides 99 codes with the added advantage of 'silent operation'. XTCSS fitted radios are purposed to enjoy more privacy and flexibility of operation.

Uses

Carrier squelch is used in amateur radio to keep repeaters from being transmitting continually. CTCSS is often used as well it keeps other nearby repeaters on the same input frequency from keying the carrier squelch repeater unnecessarily. Amateur radio, often called ham radio, is a hobby and public service enjoyed by about 3 million people[1] throughout the world. ... An Amateur radio repeater is an electronic device that receives a weak or low-level amateur radio signal and retransmits it at a higher level or higher power, so that the signal can cover longer distances without degradation. ... The word keying has a number of meanings: keying (cryptography) is the installation of key material into a device. ... The term input has a variety of uses in different fields. ...

Family Radio Service (FRS) and PMR446 radios often use 38 different CTCSS tones, also erroneously called "sub-channels". While these do not add to the available number of conversations which can take place at once in a given area, they do reduce annoying interference experienced by users. The Family Radio Service is an improved walkie talkie system authorized in the United States. ... Alan 456r PMR446 (Personal Mobile Radio, 446 MHz) is a radio frequency part of the UHF range that is open without licensing for personal usage in most members of the European Union. ... For the movie from Francis Ford Coppola, see The Conversation. ... Interference of two circular waves - Wavelength (decreasing bottom to top) and Wave centers distance (increasing to the right). ...

Professional wireless microphones use squelch to avoid reproducing noise when the receiver does not receive enough signal from the microphone. Most professional models have adjustable squelch, which is adjusted with a screw on the receiver. The first wireless microphone went into production in 1962, called the transistophone and put out by the German equipment manufacturer beyerdynamic. ...

Notes

1. ^ Source: modified from Federal Standard 1037C and from the NTIA Manual of Regulations and Procedures for Federal Radio Frequency Management in support of MIL-STD-188.

Federal Standard 1037C entitled Telecommunications: Glossary of Telecommunication Terms is a U.S. Federal Standard, issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended. ... Also known as the Red Book, this publication of the Office of Office of Spectrum Management of the National Telecommunications and Information Administration or NTIA, is the official source for all technical regulations relating to the use of the electromagnetic frequency spectrum. ... MIL-STD-188 is a series of U.S. military standards relating to telecommunications. ...

External links

• Alternative CTCSS description.
• Alternative DCS description.