18. One method of telegraphy that gives equally satisfactory operation in wire as well as in radio
communication is
a. dc polar.
b. dc neutral.
c. ac on-tone, off-tone.
d. ac frequency-shift keying.
19. The transmission mode most often used by speech-plus-duplex systems is one in which the
a. two terminals use the line alternately.
b. two terminals send in both directions simultaneously.
c. one terminal keys for mark signals and the other one keys for space signals.
d. one terminal shifts the phase of its signal to permit transmission in two directions.
20. In the speech-plus-duplex system, tone telegraph signals do not interfere with the speech signal because
of the
a. mode of operation.
b. narrowband filter.
c. dissimilar frequencies of the two terminals.
d. separate lines for speech and tone telegraph signals.
CHECK YOUR ANSWERS WITH LESSON #2 SOLUTION SHEET, PAGE 47.
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