GPS disciplined offset-frequency quartz oscillator

The global positioning system can be used to provide a precise time and frequency reference to control local oscillators. The local oscillator is necessary to provide holdover of time and frequency in the absence of GPS and to average short-term jitter in the GPS signal recovered by the receiver. This paper gives an overview of the hardware design and control strategy for converting the output of a free-running ovened quartz oscillator (OCXO) to the desired standard frequency output by reference to GPS. The method enables the use of a very low aging fifth overtone quartz oscillator, to which final plating of the crystal to trim 'on frequency' is omitted. Sufficient frequency control could not normally be applied to this very stable oscillator by the conventional method of varactor tuning. A compact implementation is achieved with very low spurious frequency content and low phase-noise of the standard frequency output. Performance data is presented.