1-9. OPERATIONAL MODES AND CONTROLS. (CONT)
INCOMING CALLS WITH MODE SELECTOR SWITCH IN AC SUPV POSITION (CONT)
When the integrator switches off, the acknowledge delay circuit also switches off. The acknowledge delay circuit is a transistor in the
timer circuit which Is normally conducting. The output of the acknowledge delay circuit supplies the positive voltage necessary for the
tone ringer circuit to function. However, when the integrator and acknowledge delay are off, the tone ringer cannot function for at least
450 milliseconds. After this period of time the telephone set is ready to accept incoming calls.
When two telephone sets are connected for point-to-point operation, a switching facility is not used. When the MODE SELECTOR
SWITCH is set to POINT TO POINT, lifting the handset of the calling telephone set will cause the following functions in the order given:
The calling telephone sends a 570 Hz signal burst for about two seconds.
The 570 Hz signal is received on the receive terminals of the called telephone set. The receive terminals are inductively coupled to the
input of the 570 Hz amplifier in the ring acknowledge tone detector circuit. However, the output of the circuit does not energize the
integrator circuit because the 570 Hz signal is modulated.
The capacitor on the input to the integrator acts as a short circuit to the modulation frequency. The detector output is used to energize
The 1633 Hz oscillator switches on and off at modulation frequency. The output of the oscillator is coupled to the tone ringer circuit
receive element. The telephone set rings at a frequency of 1633 Hz and the ringing signal is stopped at the modulation rate of the
Incoming ring signal.
When the called telephone answers, a voice path is established between the two telephone sets. If the called telephone set does not
answer, the calling party must replace the handset in the cradle and lift it again.
DC SUPERVISION MODE
When two telephone sets are connected for DC SUPV operation, the MODE SELECTOR SWITCH is set to DC SUPV position and the
telephone is connected to a switching facility which uses dc current. In this mode, seize and release tones are prevented.