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15
The resulting 455 kHz signal is
mixed up to the broadcast band
and inserted into a stereo
receiver. The stereo indicator is
turned on, and the resulting left
and right output signals are
captured on the TDS 744A scope
(Figure 15). The upper two
traces are the right channel
(1000 Hz) signal and spectrum.
The lower two traces are from
the left channel (800 Hz). The
stereo encoding was successful
with the receiver separating the
two tones by over 35 dB. The
38 kHz sub-carrier in FM broad-
cast is not unique. Higher sub-
carriers are commonly used to
encode specialized audio
channels or pager data to take
advantage of the coverage of
commercial FM transmitters.
Figure 15. After demodulation by an FM receiver,
the TDS 744A displays the left and right channels
and their spectra. The receiver separated the
800 Hz and 1000 Hz tones by over 35 dB
(spectrum scales are 250 Hz/div horizontal and
20 dB/div vertical).
Right channel and spectrum
Left channel and spectrum