Analysis and comparison of performance of frequency standard measurement systems based on beat-frequency method

The performance of two high precision frequency-stability measurement systems, analog beat method time-interval analyzer, has been compared with digital beat method systems developed at the National Time Service Center. In this paper, the digital beat method system is a measuring technique that uses a multi-channel beat note digital analyzer in place of the time interval counter. This technique uses the local oscillator and mixer to convert the test signals and reference signals to a low frequency. This article reports on the frequency-stability analysis of the digital beat method in detail based upon the beat method working at 10 MHz with 1 Hz beat note and the cross correlation arithmetic. The principle of the system is reviewed, the design approach and compared system is described, and the experimental results are present. The measurement system shows that the digital beat method system can achieve a stability of 3times10^-14 /tau (Allan deviation, tau =1s ) when the analog beat method can acquire a stability of 4.7times10^-12 /tau (Allan deviation, tau =1s ) by using the SR620. An approach to reduce quantization noise effects and evaluate performance of the algorithm problems has been tested too.