Long term time stability of conventional GPS receivers

The most important feature of GPS-receivers in time keeping is long-term phase stability and reliability. MIKES and Nokia have studied in cooperation the performance of medium price commercial GPS receivers both in the short term and long-term sense. By comparing time differences of the receivers, both short term and long-term stability can be evaluated assuming that all receivers do not drift into the same direction. A long term stability seems to be from < 1 ns/yr to about 10 ns/yr. Due to operational interrupts unexpected transient phase changes occur in some receivers. The magnitude of these permanent jumps varies from 10 ns to 50 ns. The older receivers show a diurnal phase variation of 10..20 ns. Temperature effects seem to be small though the ambient temperature can vary from -20degC to +30degC.