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In the United States, the standard "city" dial tone was a 600 Hz tone that was amplitude-modulated at 120 Hz. [3] Some dial tones were simply adapted from 60 Hz AC line current. In the UK, the standard Post Office dialing tone was 33 Hz; it was generated by a motor-driven ringing machine in most exchanges and by a vibrating-reed generator in ...
The commonly used keypad has four rows and three columns, but a fourth column is present for some applications. Pressing a key sends a combination of the row and column frequencies. For example, the 1 key produces a superimposition of a 697 Hz low tone and a 1209 Hz high tone. Initial pushbutton designs employed levers, enabling each button to ...
Equipment is required to maintain tolerances within ± 0.5% in frequency and ±1.5 dB in amplitude stability. Harmonic distortion is to be at least 30 dB below the applied tone level. [1] The tones are as follows: [2] Dial tone is a continuous tone of the addition of the frequencies 350 and 440 Hz at a level of −13 dBm.
Frequency definition Tone cadence Dial tone A: 425 Hz: continuous Dial tone B: 425 Hz, amplitude modulated by 25 Hz: continuous Dial tone C: 400 Hz + 425 Hz + 450 Hz: continuous Dial tone D: 400 Hz + 425 Hz: continuous Dial tone E: 413 Hz + 438 Hz: continuous Ringback tone A: 425 Hz, amplitude modulated by 25 Hz: 0.4 s on, 0.2 s off, 0.4 s on ...
Multifrequency signaling is a technological precursor of dual-tone multi-frequency signaling (DTMF, Touch-Tone), which uses the same fundamental principle, but was used primarily for signaling address information and control signals from a user's telephone to the wire-center's Class-5 switch. DTMF uses a total of eight frequencies.
Some central office switches in the United States, notably older GTD-5 EAX systems, utilize a single frequency tone, 480 Hz, known as High Tone for this purpose. In either case, the tone is substantially louder than any other signal transmitted over a copper POTS circuit; loud enough to be heard across a room from an unused off-hook telephone.
A dial tone (dialling tone in the UK) is a telephony signal sent by a telephone exchange or private branch exchange (PBX) to a terminating device, such as a telephone, when an off-hook condition is detected. It indicates that the exchange is working and is ready to initiate a telephone call. The tone stops when the first dialed digit is recognized.
Ringing tone is often also called ringback tone. However, in formal telecommunication specifications that originate in the Bell System in North America, ringback has a different definition. It is a signal used to recall either an operator or a customer at the originating end of an established telephone call. [ 2 ]