Crystal oscillator noise effects on the measurement of ionospheric phase scintillation using GPS

This paper presents the results of a development and testing of a software-modified commercial single-frequency NAVSTAR Global Positioning System C/A-code receiver to measure the effects of ionospheric scintillation on signals passing through the ionosphere. This product measures the difference between the received signal phase and the phase of a low-noise oven-controlled crystal oscillator (OCXO). However, even the high quality OCXOs exhibit a frequency "jumping" phenomenon that hinders the monitoring of phase scintillation. The development resulted in extensive testing of OCXOs. With minor adjustments of the supply voltage and screening or by synthesizing from a lower-frequency oscillator, this phenomenon was overcome, resulting in a successful product that is now commercially available. This paper presents details of the phase-monitoring performance using different types of oscillators and how their performance compares to ionospheric phase scintillation variations.