Meaning
High resolution phase comparison between two independent signal sources provides the necessary precision for evaluating state of the art frequency standards. The dual-mixer time difference method eliminates the noise inherent in the measurement system by using a common oscillator to down-convert both signals to a lower frequency. This architecture allows the timing jitter of the test equipment to cancel out.
Metrology labs use this approach to verify the phase noise and short term stability of oscillators sold into financial trading or aerospace markets.
Noise Cancellation
Simultaneous mixing of two signals against a single transfer oscillator ensures that any fluctuations in the local source appear equally in both channels. Because the system subtracts one channel from the other, the common noise disappears from the final result. This feature enables the measurement of stability levels that are far below the noise floor of the equipment itself.
Resolution Level
Down-conversion to a low frequency beat note allows for the use of standard time interval counters with enhanced precision. Every cycle of the original high frequency signal is represented by a much larger time period in the beat signal.
Verification Requirement
Verification of timing hardware depends on this technique. The data from a dual-mixer time difference evaluation supports the issuance of quality certificates.
