[Radio Wrangler]

The synchronous demodulation feature is on the H2900 block, but it's hidden in full view.

The synthesiser is more than a little bit weird

For minimum phase noise, it employs a huge bank of crystal oscillators mounted in a thermal mass box. One oscillator is enabled at a time and is free-running and acts as the first local oscillator. The incoming signal is mixed into an IF around 80MHz, 1 or 2 MHz wide, which uses a helical filter. A sample of the crystal oscillator signal goes to the synthesiser and is compared to the frequency standard, so the 2nD LO synthesiser can be offset to compensate for errors and drift in the crystal oscillator frequency ( Ha! shades of Wadley!) For synchronous demod, all they had to do was to extract the carrier from the final IF and compare that to the frequency standard. The frequency standard provided the reinserted carrier, and the 2nd LO synthesiser was slewed to put the signal on the right frequency for the fixed inserted carrier at the demod. The crystal oscillators no longer needed compensation, any and all causes of offset got taken into account.

David