Frequency measurement errors due to noise in LDV signals.

Analysis is presented which, for single particle Doppler signals, quantifies the ability of frequency detectors to determine the true Doppler frequency of a Doppler signal in the presence of noise. The analysis predicts the expected value of the measured frequency and shows that, in addition to signal parameters such as the signal to noise ratio and the noise band width, the measured values are also strongly affected by the type of frequency detection that is employed and by the method of signal validation. Theoretical relations for the former effect are presented for three types of detectors (frequency locked loops, phased locked loops, and counters), and experimental results obtained with simulated Doppler signals are shown to support the theory. It is found that other things being equal, the frequency locked loop produces substantially smaller errors at low signal-to-noise ratios than the other two types of detectors. Limited experimental results on the effect of the method of signal validation are also presented. (A)