Abstract: A frequency measuring apparatus is disclosed wherein a plurality of sets of harmonic signals is mixed with a received signal to produce a plurality of groups of beat frequency signals. A plurality of filters, each one being fed by a corresponding one of the groups of beat frequency signals, is provided to reject the beat frequency signals in such group having frequencies greater than one-half the fundamental frequency of the set of signals producing the group of beat frequency signals fed to such one of the filters. A plurality of counters, each one coupled to the output of a corresponding one of the filters, converts the frequency of the beat frequency signals fed to such counter to corresponding digital words. A logic network is provided to calculate the frequency of the received signal from the digital words provided by the counter.