Digital Transmission Equipment
SIDACtor
Data Book
3 - 14
Teccor Electronics
(972)580-7777
Pair Gain Circuit Protection
A digital pair gain system differs from an ISDN circuit in that ring detection, ring trip,
ring forward, and off hook detection are carried within the 64 kbps bit stream for each
channel rather than using a separate D channel. The pair gain system also uses loop
powering from 10V up to 145V with a typical maximum current of 75mA.
Protection Circuitry
In Figure 3-14, longitudinal protection is required at the Central Office Terminal (COT)
interface because of the ground connection used with loop powering. This is
accomplished using two P1800SC SIDACtor
’
s for over voltage protection and two
F1250T TeleLink fuses (one on TIP, one on RING) for over current protection. For the
U-interface side of the coupling transformer, additional over voltage protection is
shown using the P0080SA SIDACtor.
For the Customer Premises (CP) and the Remote Terminal (RT) interfaces where an earth
ground connection is not utilized, only metallic protection is required. Figure 3-15 shows
metallic protection being satisfied using a single P3100SC across TIP and RING and a
single F1250T on either Tip or Ring.
Component Selection
The
“
SC
”
SIDACtor and F1250T TeleLink were chosen because both components
meet GR 1089 surge immunity requirements without the use of additional series
resistance. The voltage rating of the P1800SC was selected to ensure coordination
with loop powering up to 150V. The voltage rating of the P3100SC was selected to
ensure coordination with POTS ringing and battery voltages.
Figure 3-13 Pair Gain Overview
Switching
System
Line powered
DSL 2-Wire,
160 kbps
2B1Q
POTS
Line 1
Line 2
MDF
Central Office
Terminal (COT)
VF
1
VF
2
HF
VF
1
VF
2
HF
Remote
Terminal
Remote Terminal (RT)
building or pedestal
mounted
POTS
Customer
Premises
(CP)
Central Office (CO)