TELEPHONE INTERFACE MODULE (TIM)

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 potentiometers 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 ∝F/1000 ft. That's why Tellabs provides a total of 0.064 ∝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.

14.14.3ADDING CAPACITANCE TO THE TERMSET

Capacitance may be added to the Termset (see Figure 14-29)by soldering non-polarized, 0.033 ∝F capacitors in paralleled with the capacitors in the balance circuit of the Tellabs Termsets. Start with the least significant capacitor (0.002 ∝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 capacitors 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 variable resistor of the 6132 balance circuit.

14-30