Whitepaper
Comb Generator as a Reference Source
This application note from Com-Power Corporation explains what a comb generator is and how it is used as a reference source in EMC testing environments. A comb generator produces a repetitive pulse with very fast rise and fall times, generating a series of harmonically related frequency components that, when viewed on a spectrum analyzer, resemble the teeth of a comb. Its compact size, battery power, instant on/off operation, and simultaneous multi-frequency output make it far more practical for lab use than a conventional RF signal generator. The primary application discussed is EMC test site validation, where the comb generator is used before each test session to verify that all components of the measurement chain — antenna, cables, connectors, preamplifier, and receiver — are working correctly. Discrepancies from previously recorded reference readings indicate a problem that should be investigated before data is collected. The document outlines six desirable characteristics for a radiated reference source, covering radiation pattern (ideally omnidirectional), battery-only operation during use, temperature stability, appropriate output power level relative to specification limits, harmonic step size to control energy density, and usable frequency range. For conducted reference sources, ease of connection to the LISN and stable output are highlighted. The note also covers how a comb generator can be used to evaluate the quality of anechoic chamber absorber material by comparing readings taken at two slightly different positions within the chamber.