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The original plan had two slightly different versions of this signal, with a cadence of 0.2 of a second ON and 0.3 of a second OFF to signal toll-circuit congestion and a cadence of 0.3 of second ON and 0.2 of a second OFF for local reorder. High tone is a tone of 480 Hz at –17 dB.
The tone frequencies, as defined by the precise tone plan, are selected such that harmonics and intermodulation products will not cause an unreliable signal. No frequency is a multiple of another, the difference between any two frequencies does not equal any of the frequencies, and the sum of any two frequencies does not equal any of the ...
Dial tone for the precise tone plan found on public switched telephone networks in North America: −20 dBm: 10 μW: −30 dBm: 1.0 μW = 1000 nW: −40 dBm: 100 nW: −50 dBm: 10 nW: −60 dBm: 1.0 nW = 1000 pW: The Earth receives one nanowatt per square metre from a magnitude +3.5 star [15] −70 dBm: 100 pW: −73 dBm: 50.12 pW
o o o s. c: o thO 00 . Created Date: 9/20/2007 3:37:18 PM
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In North America, the Precise Tone Plan used today employs two tones of 480 and 620 Hz at an amplitude of -24 dBm with a 0.5 s on/off cadence. Prior to the adoption of the PreciseTone system, the busy signal generally had the same frequency as the dial tone. Until frequencies began to be standardized in the 1960s, telephone signals varied from ...
The Precise Tone Plan for the North American Numbering Plan of the US, Canada, and various Caribbean nations specifies a combination of two tones (350 Hz and 440 Hz) which, when mixed, creates a beat frequency of 90 Hz. The UK dial tone is similar, but combines 350 Hz and 450 Hz tones instead, creating a 100 Hz beat frequency.
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