Digital filters for obtaining quadrature components of a periodic signal

Abstract

A digital filter for obtaining quadrature components in a periodic signal, such as the recovery of phase and/or amplitude of two or more periodic signals through coherent digital summation techniques. In one embodiment of the invention, the digital filter forms part of an omega type radio navigation system in which a mobile receiver station receives a signal containing three preselected frequencies of interest transmitted from a plurality of fixed transmitting stations in timed sharing sequence. The mobile receiving station may contain band pass filters to receive the signal and separate and pass only the three preselected frequencies of interest. These three preselected frequencies of interest are then summed and introduced into a sample and hold circuit which operates in combination with an analog-to-digital converter. In this way, the digital equivalent of each of these three preselected frequencies are generated on a pre-established sample time basis so that digital binary numbers represent the voltages of the frequency samples. A data processor receives the binary number equivalents of these frequencies and generates a phase relationship between the preselected frequencies. In this way, when the digital filter forms part of the omega type navigation system, it is possible to thereby determine the location of the mobile receiving station relative to the fixed transmitting stations.

Dependencies are inferred from the claim text.