Evaluation of the tie of a crystal clock by gps measurements with negative sawtooth correction and unbiased fir filtering

The local crystal clock performance is evaluated in terms of the time interval error (TIE) that is a measure of inaccuracy in timekeeping. In this paper, we apply the unbiased FIR filter to examine the TIE by the GPS timing receiver with and without the negative sawtooth correction. The rubidium clock is used as a reference source of 1 PPS signal for the local crystal clock. We show that the unbiased FIR estimate is comparable to measurements with the sawtooth correction. Herewith, the estimate becomes much more accurate when the TIE changes with time very slowly.