Abstract: Disclosed is an apparatus and process for indicating or measuring the frequency of an incoming signal of unknown frequency. The system includes a plurality of processing channels, each of said channels including a pair of oscillators offset in frequency coupled to a pair of harmonic generators for producing respective output signals harmonically related, wherein the fundamental frequency of said harmonic generators are correspondingly offset. A combination of mixers, filters, amplifiers, and frequency-to-voltage convertors are utilized in combination with logic comparator means for producing analog voltage signals representative of the unknown frequency. Examples of utilization and display of these analog signals are illustrated.