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.