The AR6A Single-Sideband Microwave Radio System: Frequency control

The AR6A Radio System requires precise control of the local oscillator frequency at repeaters and main stations, so that the IF equalizer pilots will be accurately located with respect to the narrowband crystal pick-off filters. In addition, the accumulated frequency error from each repeater and main station must be limited to a value that can be corrected by the tracking receiver of the multimastergroup terminal. Precise frequency control is maintained along the route by locking local oscillators to a stable and accurate frequency reference provided at each repeater station by the Microwave Carrier Synchronization Supply (MCSS). The MCSS provides a source and a backup for this signal. Extensive monitoring circuitry in the MCSS detects failed conditions. The accuracy of the two oscillators is continuously monitored by making frequency comparisons of their output. These frequency-monitoring circuits are also used to make yearly adjustments to the oscillators using a rubidium frequency standard as reference. This paper describes the MCSS System that has been developed for the AR6A Radio System.