Experimental Comparison of the Unbiased FIR Estimates vs. the Sawtooth Correction in GPS-based Timekeeping

The trade-off is investigated experimentally between the real-time unbiased FIR estimates of the time interval error (TIE) model of a local clock and the sawtooth correction implemented to the measurement set. We exploit the crystal oscillator embedded to the Stanford Frequency Counter SR620 as a local clock and rubidium oscillator attached to SR625 as a reference clock. The SynPaQ III GPS Sensor is used as the GPS timing receiver. We show that the unbiased FIR estimates produce a lower error than the sawtooth correction. The error becomes much lower when the TIE changes very slowly. The unbiased FIR estimates of the fractional frequency offset are consistent to the rubidium measurements and produce much lower noise than in the measurements with the sawtooth correction