Novel Microhertz Comparison Measurement of Remote Frequency Standards : Fast Micro-Hertz Measurement of Frequency by Phase

Measuring frequency by phase is demonstrated practically to be greater than a hundred times faster than direct frequency measurement. Even on remote off-air radio frequency standards affected by radio propagation variations, microhertz accuracy can be achieved in hours rather than weeks. And this at low cost by using readily available SDR techniques. The novelty is the use of a large (21 bit) high precision (24 bit) FFT on a signal translated to IFs at about 70 to100 Hz and with FFT window lengths of a few minutes. These first results indicate that this novel technique could in the future compute Allan Variances perhaps a hundred times faster than the longest stated ‘observation-time’. This frequency-by-phase fast measurement technique is also compared with a frequency-bin-interpolation technique.