Tellabs 6971 Technical Manual

"'teIIabs
technical manual
76-816971
rev B
practice section 816971
©
Tellabs Inc., 2 April 1980
all rights reserved, printed in USA
6971 Common Interface Module
(2W/4W)
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page 2
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page 6
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contents
section 1 general description
section 2 application
section 3 installation
section 4 circuit description
section 5 functional schematic
section 6 specifications
section 7 testing and troubleshooting
1. general description
1.01 The 6971 Common Interface Module (fig-
ure 1) provides transmission interface between
4wire transmission equipment and a 2wire or 4wire
telephone station loop or a PBX trunk. Both ad-
justable transmission attenuation and switch-selec-
table 4wire-to-2wire conversion are provided. As an
alternative to 4wire-to-2wire conversion, the 6971
may be switch-optioned to provide a 4wire-to-4wire
pad/transformer interface. In addition, the 6971
accepts several types of optional signaling conver-
ter plug-on subassemblies that provide various
modes of loop-to-E-and-M and E-and-M-to-OX sig-
naling conversion.
1.02 Levels in both the transmit and receive chan-
nels may be prescription-set via front-panel switches
that introduce from 0 to 26.5dB of attenuation, in
0.1 dB increments, into the transmit and receive
4wi re paths.
1.03 An integral two-coil hybrid provides 4wire-
to-2wire transmission path conversion. A switch
option, however, conditions the 6971 to provide
4wire transmission between the transmission equip-
ment side and the facility side. The 4wire option
provides adjustable transmission attenuation with
transformer isolation and balance.
1.04 Switch able 600 or 900-ohm terminating
impedance is provided on the facil ity side of the
6971 when the module is optioned for 2wire loop
operation. The facility-side terminating impedance
is fixed at 600 ohms when the module is optioned
for 4wire loop operation. The 600 or 90o-ohm re-
sistive component at the 2wire port is in series
with a 2.151lF capacitive component. On the equip-
ment side of the 6971, terminating impedances are
fixed at 600 ohms.
1.05 The 6971 module is designed to accept
Tellabs' series of 9961X loop-to-E-and-M and E-
and-M-to-OX Signaling Converter plug-on subassem-
blies. The 9961A subassembly, when used on the
6971, provides conversion between local E-and-M
signaling leads and foreign-exchange station-end
(FXS) loop signaling. The 9961B subassembly pro-
vides conversion between E-and-M signaling and
foreign-exchange office-end (FXO) loop signaling.
page
1
figure 1. 6971 Common Interface Module
The 9961C subassembly provides conversion be-
tween E-and-M signaling and switchboard (ac) or
manual (dc) ringdown loop signaling. The 99610
subassembly provides E-and-M-to-duplex (OX) sig-
naling conversion. Signaling conversion is provided
when the 6971 is optioned foreither 2wire or 4wire
operation.
Note: When OX signaling is used (9961DJ, the OX
signaling path derived via the 6971 includes only
the transmit loop, as access to the receive-loop
simplex lead is not available.
1.06 The 6971 is equipped with a compromise
balance network that provides 600 or 900- ohm
impedance in series with 2.151lF capacitance when
the module is optioned for 2wire loop operation.
Network build-out (NBO) capacitors associated
with this balance network provide from 0 to
0.1261lF of NBO capacitance in 0.0021lF in-
crements. If precision balancing of the hybrid is
desired, a Tellabs 993X Precision Balance Network
(PBN) subassembly may be plugged into a recep-
tacle on the 6971 's printed circu it board and the
compromise network switch-optioned out of the
circuit. Refer to the 993X Tellabs Practice for de-
tailed information on these PBN SUbassemblies.
1.07 The front panel of the 6971 contains, in
addition to the aforementioned attenuation
switches, two light-emitting diodes (LE D's) that
light to indicate seizure in either direction (i.e., to
indicate E-Iead and M-Iead status) and two sets of
test points to access the equipment-side receive in-
put and transmit output ports.