A precision sidereal telescope drive based on a solar time crystal clock

A requirement arose for a sidereal drive for a small microwave radiometer on an equatorial mount, the equipment to run unattended to a precision of about 2 minutes in hour angle over a 7-day period. The installation already included a solar-time crystal clock based on a IO MHz oscillator (type HCD 25), which through decade scalers could easily be arranged to operate a standard 50 Hz synchronous motor which would drive the mounting at one revolution per solar day. However, no suitable gearing was available to generate the required sidereal rate.