Tellabs 7501 Technical Manual

7tellabs
technical manual
76-837501
rev A
practice section 837501
©
Tellabs, Inc., 1 November 1983
all rights reserved, printed in USA
7501 Dial Long Line Module
(LSO~)
page T
page 2
page 5
page 7
pageB
page 9
page 9
contents
section T general description
section 2 application
section 3 installation
section 4
circuit description
section 5 block diagram
section 6 specifications
section 7 testing and troubleshooting
1. general description
1.01 The 7501 Dial long Line module (figure 1)
regenerates signaling and supervision to increase
the range of a loop-start or ground-start CO or PBX
line circuit in applications where a station served
by a metallic facilitY is located beyond the normal
range of the switching equipment. An integral re-
peat coil extends a separate source of locally de-
rived loop current toward the station. On calls to
the station, the 7501 bypasses ringing generated at
the switching equipment or repeats ringing (starts
and applies local ringing generator), as selected by
switch option. When the station answers, the 7501
trips ringing. On calls from the station, the 7501
detects and regenerates off-hook states and repeats
dial pulsing.
1.02 This practice section is reissued to docu-
ment the addition of option switches STT and ST2,
which allow you to select either a standard wiring
scheme or Tellabs universal wiring scheme. This
change resulted in the Issue 3 version of the mod-
ule (Tellabs part number 837501).
1.03 The 7501 accommodates short ringing
intervals typical of PBX's that use nonstandard
ringing sequences for precedence or prioritY alert-
ing. The module can reliably accommodate ringing
bursts and silent intervals as short as lOOms. Ring-
up and release delays are essentially symmetrical so
that the ringing intervals are not shortened as they
are repeated through the 7501. In addition, an
option switch permits extension of each ringing
interval by approximately 1 second. This option is
intended primarily for use in off-premises-station
(OPS) applications where a short ringing interval
from a PBX may not be recognized by ringing de-
tectors or alerting devices at a distant central of-
fice or station location.
1.04 The 7501 can be switch-optioned to ac-
commodate 48, 12, or 96Vdc talk-battery operation.
The module's maximum signaling range for on-hook/
off-hook detection is 3000 ohms of loop resistance
with 48Vdc talk battery, 4500 ohms with nVdc,
and 6000 ohms with 96Vdc. At 48Vdc talk battery,
the 7501 provides 13mA of loop current with
3000 ohms of cable resistance and 600 ohms of com-
bined station-instrument and internal-Dll resist-
*
loop start only
figure 7. 7507
Dial Long Line module
ance. When the 7501 is connected to a telephone
set (instead of to another Dll in a tandem arrange-
ment), the aforementioned ranges are somewhat less
because a telephone set requires more loop current
for proper operation (20 to 23mA) than does a
DlL. See section 2 of this practice for details.
1.05 The 7501 is designed so that, in repeated-
ringing applications, a ring-generator bias potential
equal to the talk-battery potential provides a ring-
trip range equal to the module's signaling range.
Thus, the 7501 will reliably trip ringing at up to
3000 ohms with 48Vdc ring generator bias, up to
4500 ohms with nVdc bias, and up to 6000 ohms
with 96Vdc bias.
1.06 The 7501 provides a switch-selectable
choice of 600 or 900-ohm terminating impedance
on both the switching-equipment and station sides
of the module. In addition, the module can be
switch-optioned to interface associated 2wire or
4wire transmission equipment on each side. Addi-
tional features and options of the 7501 include
solid-state ring-detection and ring-trip circuitry,
ring trip during either silent or ringing intervals,
loop-current limiting, signal and transient limiting,
and relay operation to enable an associated voice-
frequency repeater when the circu it is busy and to
disable it when the circuit is idle. The 7501 ac-
cepts two optional plug-on subassemblies: The
Tellabs 9901 Pulse Corrector for precision dial-
pulse correction and the Tellabs 9906 Reverse-
Battery Adapter for use on circuits with reverse-
battery supervision. Without the 9901 subassembly,
dial-pulse distortion of the 7501 is less than 5 per-
cent.
1.07 A front-panel lED on the 7501 lights to
indicate circuit-busy conditions. Also located on the
module's front panel are four test points that pro-
vide access to the switch-side and station-side tip
and ring leads.
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