Positron Teleline 751221, Description And Installation

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751221
6 Standalone Telephone Unit
Hybrid Voice Circuits
The Hybrid Voice Circuits located on both the Station and CO sides of the card
form a two-wire to four-wire to two-wire configuration that permits the
separation of Transmit (TX) and Receive (RX) signals. These circuits also
perform an impedance matching function such that the Station side impedance is
reflected to the CO side. This renders the card effectively transparent for
communication purposes.
Ring Detector
The Ring Detector is a bandpass filter centered about 20 Hz. It detects ringing
signals and sends 40 Hz pulses to the ring generator on the Station side, via a
digital opto-coupler.
Digital Opto-Isolators
Each Digital Opto-Isolator consists of a light emitting diode (LED) and a
phototransistor pair, connected with a plastic fiber optic cable for isolation. They
provide digital signal transmission across the isolation gap.
Transmit and Receive Analog Opto-Isolators
The Transmit and Receive Analog Opto-Isolator employs feedback circuitry to
“linearize” the behavior of its LED/photodiode pairs, thus providing for
undistorted lightwave analog signal transmission across the air gap. Feedback
also makes it possible to compensate for the aging of the LEDs, ensuring that the
performance of the unit does not degrade over time.
Ring Generator
The Ring Generator receives 40 Hz pulses from the CO side and regenerates a
ringing signal at the same frequency and synchronism as the CO side.
On-hook/Off-hook Switch
The On-hook/off-hook Switch is a metal oxide semiconductor field effect
transistor (MOSFET) current limiting circuit that is turned on by the off-hook
signal. When switched on, it permits modulation of the hybrid voice circuits.
Off-hook Detector
The Off-hook Detector transmits a signal to the CO side to go off-hook when the
telephone is lifted.