Rev. 1.0
Principles of Operation
4—5
4.3.2
Stereo Generator
The 19 and 38–kHz subcarriers are digitally synthesized from a master 7.6 MHz
crystal oscillator. The 1.52 MHz clock signal used by the low-pass filter is also
derived from the 7.6 MHz master oscillator.
Stereo signals are generated by a four-quadrant, analog multiplier. The output of
multiplier is the product of 38 kHz applied to the “X” input and the difference of left
and right audio (L-R signal) applied to the “Y” input. The resulting output is a
double sideband, suppressed carrier—the L-R subcarrier.
An analog switch at the input of the stereo generator provides selection of left and
right audio for stereo and mono modes. In the mono mode, right channel audio is
disabled and the left channel audio is increased from 45% modulation to 100%.
4.3.3
SCA Input
The SCA subcarrier, the left, right, and left-minus-right subcarriers, and the 19–kHz
pilot subcarrier are combined into the composite stereo signal by a summing
amplifier. The output of the summing amplifier is buffered to drive both the RF
synthesizer and the front panel display.
4.3.4
Processed Audio
A de-emphasis network samples the stereo generator input signals and routes the
de-empasised audio to the back panel to be used for a studio monitor and for audio
testing. Jumpers JP203 and JP204 select between 75 and 50 µsec.
