2-53
Thus, with the 4-digit code of figure 2-50 and 2-51, the quantizing noise will be about 35 dB weaker
than the peak signal which the channel will accommodate.
The advantages of pcm are two-fold. First, noise interference is almost completely eliminated when
the pulse signals exceed noise levels by a value of 20 dB or more. Second, the signal may be received and
retransmitted as many times as may be desired without introducing distortion into the signal.
Q-27.
Pulse-code modulation requires the use of approximations of value that are obtained by what
process?
Q-28.
If a modulating wave is sampled 10 times per cycle with a 5-element binary code, how many
bits of information are required to transmit the signal?
Q-29.
What is the primary advantage of pulse-modulation systems?
SUMMARY
Now that you have completed this chapter, a short review of what you have learned is in order. The
following review will refresh your memory of angle modulation and pulse modulation.
FREQUENCY-SHIFT KEYING (fsk) is similar to cw keying in amplitude modulation and is a
form of angle modulation. The carrier frequency is changed between two discrete values by the opening
and closing of a key.
