Section 365–336–202
4
The adjusted VF signal is then routed through transformer T2 which provides dc isolation from the line and a bal-
anced output level. The signal is then fed to the T1 & R1 leads (pins 8 and 7) via the LINE and DROP jacks.
4.3
Sealing Current
Three different configurations of Sealing Current are provided and are selected by option Switch S1.
The SX (Simplex) position supplies ground to leads T and R and –48Vdc, through a 750-ohm thermistor, to leads
T1 and R1. When the module is first plugged in, the current surges to approximately 100mA and decreases
quickly to a steady simplex current of approximately 30mA. This low value of dc current being applied to the 4W
cable pairs, on a simplex basis, will break down any resistance film which may build up at nonsoldered splices.
Continued application of this dc sealing current sustains the normal resistance of the cable pairs and prevents
degradation of transmission performance.
In the LP (Loop) position, the simplex leads of T1 and T2 are shorted together. Sealing current from the analog
facility will be looped by the channel unit.
The OPN (Open) position is used when no sealing current is required.
XDATA
4W OUTPUT
RANGE +13
TO
-19.5dBm
R 48
T 50
R1 7
T1 8
T-SIG
S11-1
S1-A
LP
SX
OPN
OPN
LP
S1-B
SX
4W INPUT
RANGE
-19.5 TO
+13dBm
PC board connector pin
NOTES:
XXXX
SEALING
CURRENT
GENERATOR
T1
T2
RELAY
LB
LOOPBACK
1.
2.
3.
4.
MLB
LB
LINE
DROP
T1&R1
LINE
DROP
T&R
-48V
XMT LEVEL
CONTROL
S2 & S3
FILTER
ENCODER
LB
LOOPBACK
LEVEL
CONTROL
S6
S7
&
LB
RCV LEVEL
CONTROL
S4 & S5
FILTER
DECODER
RDATA
R-SIG
S11-2
DIS
TO
4
20
DIS
LB
S8-1
S8-2
S8-3
TONE
DETECTOR
CIRCUIT
5.
Ganged switches are indicated by alphabeti
cally suffixed reference. Numerical suffix de
notes discrete switch within a package.
N. O., N. C. Relay contact
Frontpanel marking
Signal flow direction
Figure 3. 3653–36 Block Diagram