14. Telephone repeaters include facilities to change two-wire circuits to
four-wire inside the repeaters.
This is made necessary by the fact that
repeaters normally have
a. bidirectional amplifiers that raise signal level the same amount in
each direction of transmission.
b. series-connected amplifiers so as to reinforce feedback in the loop
from one telephone transmitter to its receiver.
c. two amplifiers in cascade because one amplifier seldom has sufficient
gain to overcome line loss.
d. two amplifiers, one for each direction of transmission.
15. Using a 4-kHz circuit to pass frequencies of 0.3 to
3 kHz
may be
detrimental to voice communication because
a. more power will be needed for the same distance.
b. the added complexity of equipment increases cost.
c. all end instruments
must
be
changed
to
accommodate
the
increased
d. the unused portion of the baud allows passage of additional noise and
crosstalk.
16. Careful installation and maintenance of a telephone system can be negated
by carelessness of the user.
How can the user improve the quality of the
received voice?
a. Shield the microphone and the earpiece against background noise.
b. Speak with a firm voice and clear
pronunciation,
and
shield
the
microphone against background noise.
c. Shield the earpiece against background noise, and keep the telephone
away from power lines.
d. Keep the telephone away from power lines, and speak with a firm voice
and clear pronunciation.
17. The relative interfering effect of noise depends on its frequency, as
shown in figure 1-1.
If the interference is produced by four tones of a
telegraph carrier terminal the tone that will have the greatest interfering
effect is
a. 425 Hz.
c. 1,155 Hz.
b. 765 Hz.
d. 2,795 Hz.
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