EFJohnson 3000 SERIES - Manual (Page 140)

TELEPHONE INTERFACE MODULE (TIM)
14-30
12.Monitor the Exciter deviation.
13.Adjust R41 (Rx Audio) on the E&M Main Board
such that
±
3 kHz is transmitted from the Exciter (
±
1
kHz data +
±
2 kHz audio).
14.Make several calls, interconnect and dispatch
comparing the levels. Make minor adjustments as
needed to ensure interconnect and dispatch are the
same level. While the E&M Main Board potenti-
ometers can be used for this fine tuning, it will be
more convenient to use the Termset dip switches.
15.Remove the tone from Tip and Ring, and tear down
the call. This telephone line is now tuned such that:
a.
±
2 kHz into the Receiver results in -7 dBm at
Tip and Ring.
b. Standard audio from the CO results in
±
2 kHz
Exciter audio transmitted.
c. Network equipment is balanced to the telephone
lines.
d. Interconnect/Dispatch levels are equal.
14.14 BALANCING TO THE CENTRAL OFFICE
14.14.1 INTRODUCTION
Tellabs places a circuit on their Termsets that
balances to 4k/ft of standard 2-Wire line. This is 24
gauge cable with specification of 0.016
µ
F/1000 ft.
That's why Tellabs provides a total of 0.064
µ
F of
capacitance in their balance circuit.
14.14.2 STATISTICS
The Tellabs 6132 has a maximum line drive
capability of 7.2 miles. The capacitance specification
for 24 gauge (commonly used) station cable is
0.044 µF/mile. The maximum capacitance of a line
will therefore be 7.2 x 0.084 mF = 0.605 mF. But, the
maximum capacitance of a 6132 balance circuit is
0.064 µF.
These figures show that it may be necessary to
add additional capacitance to the 6132 balance circuit
to improve the balance.
14.14.3 ADDING CAPACITANCE TO THE
TERMSET
Capacitance may be added to the Termset (see
Figure 14-29) by soldering non-polarized, 0.033
µ
F
capacitors in paralleled with the capacitors in the
balance circuit of the Tellabs Termsets. Start with the
least significant capacitor (0.002
µ
F) and work
towards the most significant if necessary. See the
handout for the 6132 for the locations of these capaci-
tors.
14.14.4 RURAL AREAS
It will be typical of rural sites to find that the 2-
Wire line leading to the CO (and, eventually, another
hybrid to convert to 4-Wire for the telephone
company) is longer than 4000 feet. When this is the
case, the capacitance in the Tellabs balance circuit is
inadequate for the task. If all of the Termset capaci-
tors have been placed in line to minimize the balance,
then try placing (soldering) additional capacitors
across the LSBs of the Tellabs cards as described
above.
14.14.5 URBAN AREAS
In other cases, there may not be enough cable
between the Termset hybrid and the CO hybrid. Near
large building (e.g. hotels, office buildings, etc.) the
CO will place a SLIC pedestal, or digital switcher. In
these cases, there may only be a few hundred feet
between the Tellabs hybrid and the CO hybrid. This is
likely the case if, when balancing, the addition of any
capacitance at all degrades the balance. All that can be
done to minimize reflected energy is using the vari-
able resistor of the 6132 balance circuit.