Techniques for improving the accuracy of frequency measurements on proton precession signals

Abstract

A statistical data processing technique has been implemented by which a significant improvement in accuracy can be achieved when measuring the frequency of noisy sinusoidal signals with an exponential amplitude decay as is the case with free proton precession signals (originating from a proton magnetometer sensor), where the highest accuracy is desired for the shortest observation time. A least square error curve fit method was used and weighing factors were introduced to compensate for the exponential decay of the signal into the noise floor. Additionally, a hardware demodulation process was implemented, enabling a higher quantizing accuracy to be achieved using the same frequency counter clock. Both techniques were realised with appropriate hardware and software and the results confirm the improvement in accuracy.