Multi-channel Beat-Frequency Digital Measurement system for frequency standard

A multi-channel beat-frequency digital measurement system (BFDMS) using digital signal processing method has been developed and operated in NTSC. The system can high-precision analyze and monitor high-stability frequency sources. It consists of three independent measuring channels what can be operated simultaneously and one calibrating channel to correct the systematic error. This result that the measured noise floor Allan deviation is approximately 3e-14 at one second has been approved in system test. The key technique is the digital correlation algorithm that has been designed to reduce the effecting of beat-frequency device noise floor on measurement accuracy. So the limit factor of improving measurement precision that is brought by circuit noise of beat-frequency technology has been solved. The algorithm can calculate phase difference either. To improve ability of measurement, the system has a calibration channel what is designed to remove the systematic error. In this channel, the known reference frequency can be used to deduce systematic error. And then this result will be used to modify the value of measurement channels. The principles of operation, and error analysis have been verified will be introduced in detail in this article.