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Appendix F
Tone Signalling
The system contains different tone signals, used to indicate status or
action of the user, on 4 different frequencies: 450, 900, 1440 and
1800 Hz. The figure below illustrates the tone signals of different
purposes:
1800 Hz
1440 Hz
900 Hz
450 Hz
1 sec.
DISTRESS IN
PROGRESS
DISTRESS HAS
BEEN SENT
DEEP
HIGH
TOGGLE HIGH
TOGGLE SLOW
HIGH DUAL
DEEP DUAL
DISTRESS
RECEIVED
BUSY
READY
CONNECTION
WAITING FOR
NON
EXISTING
ANSWER
CONNECTION
RECEIVING CALLS
TRANSMITTING CALLS
ALARMS
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