Documentation is much more detailed than seen with other kit manufacturers.
I must confess that at that time, I did not clearly understand the subtler nuances of generating stereo signals, preferring to look at Exciters and RF Amps instead. Have a stable, exact 19 KHz Sine wave Pilot Tone. Internally generate a 38 KHz signal which is in phase with the 19 KHz Pilot. This is needed for the Multiplexor. Time Division Multiplex the Left and Right Audio channels generating the least amount of harmonics.