July 2002
Intermediate to advanced
344 pages
8h 37m
English
Content preview from Newnes Radio and RF Engineering Pocket Book, 3rd Edition
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16.4 Standard PSTN tones
Signal
UK USA
Tone
Frequency
Sequence
Frequency
Sequence
Number unobtainable 400 Hz Continuous 500 + 600 Hz Interrupted every second
Number busy 400 Hz 0.75 s on, 0.75 s off 480 + 620 Hz Interrupted once per second
System busy 400 Hz 0.4 s on, 0.35 s off, 480 +620 Hz Interrupted twice per second
0.225 s on, 0.525 s off
Dial tone 50 Hz 350 + 440 Hz
33.3 Hz
Ringing tone 400 Hz, or 0.4 s on, 0.2 s off, 440 + 480 Hz Interrupted once per second
400 + 450 Hz, 0.4 s on, 2 s off
modulated by
17, 25, or 50 Hz
Pay tone 400 Hz 0.125 s on, 0.125 s off
Time tones 900 Hz 0.15 s on, 0.85 s off. Three
times every three minutes
Recorder warning 1400 Hz
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