Use of GPS ASHTECH Z12T receivers for accurate time and frequency comparisons

Area of Science:

• Metrology
• Geodesy
• Time and Frequency Standards

Background:

• Accurate time and frequency comparisons are crucial for scientific advancements.
• Existing GPS receivers require modifications for high-stability metrology applications.
• The Bureau International des Poids et Mesures (BIPM) and Laboratoire Primaire du Temps et des Frequences (BNM-LPTF) utilize GPS for precise measurements.

Purpose of the Study:

• To evaluate the performance of modified ASHTECH Z12T GPS receivers for time and frequency comparisons.
• To identify and mitigate sources of noise and systematic effects in GPS phase measurements.
• To assess the feasibility of using GPS phase measurements for high-precision frequency comparisons between remote locations.

Main Methods:

• Utilized two modified ASHTECH Z12T GPS receivers for phase measurements.
• Compared receiver performance in various antenna configurations.
• Implemented temperature stabilization for antennas and receivers.
• Conducted frequency comparisons between hydrogen-masers at BNM-LPTF and PTB using similar GPS receivers.

Main Results:

• Short-term noise levels of 1.1 to 3.5 picoseconds (ps) were observed.
• Temperature sensitivity was identified as a limiting factor for GPS phase method performance.
• Temperature stabilization of antennas and receivers significantly reduced systematic effects.
• Achieved a relative frequency stability of approximately 3.3x10^-15 for an averaging time of 15,000 seconds.

Conclusions:

• Modified ASHTECH Z12T GPS receivers can achieve high precision for time and frequency comparisons.
• Temperature control is essential for minimizing systematic errors and maximizing performance.
• The GPS phase method, with proper stabilization, offers a viable alternative for comparing remote frequency standards.