Abstract: Disclosed is a high resolution frequency measuring system which uses a frequency counter for a coarse reading and a frequency to voltage converter for a vernier reading, which readings are combined. Two types of converters are disclosed. One embodiment comprises an input terminal for receiving an input signal frequency and a pulse shaper for converting the input signal to a first train of pulses. The pulses are applied to a delay means to produce a second train of pulses delayed with respect to the first train of pulses and the first and second trains of pulses are applied to first and second inputs of a phase detector, e.g. a flip-flop. In another embodiment, delayed and undelayed versions of the input signal are fed to separate pulse shapers and then to the inputs of the phase detector.

Abstract: A low frequency radio position location system for aircraft or other vehicles for operating in conjunction with ground stations transmitting at a first VLF radio frequency which is shifted in frequency by a small amount to a second frequency at fixed intervals with the shifting being carried out coherently with a defined transition point at the frequency signal is made up of an RF receiver and amplifier, a phase-locked loop for providing a continuous output frequency signal precisely locked to the first frequency, a detector for deriving a signal at the modulation frequency, a phase comparator for comparing the phase relationship of the derived modulation frequency signal to the phase relationship of the output frequency signal and the second frequency signal. The derived modulation frequency signal and its phase information is then available for providing distance and position information in relation to the ground stations.