Service Manual

PAGE 36 TECHNICAL DESCRIPTION
links F3 and F4 can be fitted to provide bias volts. This allows the unit to use DC
signalling.
4.2.2.8 PSTN Interface
A Clare DAA chip (U7) provides a PSTN interface. An audio channel links the telephone
port to a codec (U54).
At the time of configuration, the audio levels of the PSTN interface should be set for
optimal transmission and reception.
PSTN Interface Specifications:
Isolation
Characteristics
3000 Vrms rated isolation voltage; 2000V/μs rated surge rise time.
Continuous
Output Current
130 mA (max where Rzdc = 8.2Ω).
Ringing Signal
Detect Level
5 Vrms (min for 68Hz applied to tip and ring); 28 Vrms (min for 15Hz
applied across tip and ring).
Frequency
Response
30 to 4000Hz (166Hz to 4000Hz for Snoop Circuit).
Ringer
Equivalence
0.01B REN.
Return Loss
26 dB (typical, into 600Ω at 1800Hz).
Insertion Loss
-0.4dB to 0.4dB (Tx and Rx, 30 to 4000Hz).
Tx/Rx Level
2.2Vp-p (max) for a single-tone sine wave.