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Problems

1. Two simple telephone sets each composed of a 50-ohm transmitter and a 75-ohm receiver are to be connected by a 500-foot 22-gauge cable circuit and fed by a 12-volt battery in series midway between the two sets. For maximum direct current through the transmitter, should the transmitter and receiver at each end be in series or parallel?

2. For what distance is the efficiency of the two connections the same as judged by the transmitter current?

3. The internal impedance as measured between the output terminals of a typical local-battery telephone set at a frequency of 1000 cycles is 433 ohms effective resistance and 0.043 henry inductance. This set delivers an alternating voltage of 0.70 volt to a 600-ohm load when the transmitter is excited by a 1000-cycle tone. Calculate the open-circuit voltage of the set.

4. Referring to Fig. 16, the direct-current resistance of the various units is as follows: each repeating coil winding, 22.5 ohms; supervisory relay (S.R.), 9.4 ohms; line relay (L.R.), 1000 ohms for each winding; transmitter, 50 ohms; receiver, 80 ohms; induction coil primary, 9 ohms, and secondary, 14 ohms; ringer, 1400 ohms. The set is connected to the central office by one mile of 22-gauge cable, and the battery voltage is 24 volts. Calculate the current which will flow from the central office, and the current through the transmitter, when the receiver is removed from the hook.

5. Make the same calculations for the circuit when the operator plugs in on the line and the receiver is off the hook.

6. The inductors or telephone "retard coils" of Fig. 19 have a direct-current resistance of 20 ohms, line A has a resistance of 600 ohms, and line B has a resistance of 100 ohms. The battery voltage is 24 volts. Calculate the currents that will flow through 100-ohm transmitters in the sets A and B. Now assume that the connections are as in Fig. 20(b) and that each winding has a resistance of 20 ohms. Calculate the currents that will flow through the same transmitters at A and B as before.

7. Seven central offices exist in an exchange area. Each office must have a trunk cable to each other office. How many trunks will be required for the arrangement of Fig. 22? If six offices are located on the circumference of a circle having a radius of 6 miles and one office is at the center, estimate the trunk miles saved if the tandem system of Fig. 23 is used. Assume that the number of trunk circuits between each office must be the same.

8. Draw a diagram similar to Fig. 27 for a system that theoretically will handle a maximum of one million lines. Explain how a call is completed to a given party.



Last Update: 2011-05-18