Page 311 - Satellite Communications, Fourth Edition

Digital Signals 291

Figure 10.5 Compressor characteristics. Input and output voltage scales
are normalized to the maximum values.

otherwise the systems are incompatible, and conversion circuitry is
required for interconnections such as might occur with international
traffic. The MC145500 can be configured for use with either law through
appropriate pin selections, but of course the transmitting and receiving
functions must be configured for the same law.
In the receiver, the output from the D/A converter is passed through
a low-pass filter which selects the original analog spectrum from the
quantized signal. Its characteristics are similar to those of the low-pass
filter used in the transmitter. Apart from the quantization noise (which
should be negligible), the final output is a replica of the filtered analog
signal at the transmitter.
With a sampling rate of 8 kHz or 8000 samples per second and 8 bits
for each sample codeword, the bit rate for a single-channel PCM signal is

R 8000 8 64 kb/s (10.6)
b
The frequency spectrum occupied by a digital signal is proportional
to the bit rate, and in order to conserve bandwidth, it may be necessary
to reduce the bit rate. For example, if 7-bit codewords were to be used,