A practical non‐Stark modulated double resonance microwave spectrometer has been constructed and tested in which frequency modulation is applied to one (strong) microwave source, the power from which passes through the sample gas but is prevented from reaching the crystal by filters. The second source does reach the crystal but is unmodulated. The modulation is therefore transmitted to the crystal and tuned amplifier exclusively via the phenomenon of double quantum absorption. The only transitions observed were those which occur as active pairs involving a common energy level, the two frequencies being near the two source frequencies. This provides extremely specific spectra for identification in complex situations, and is a convenient way of searching for linked transitions which are useful for assignment purposes. Because no Stark electrode is needed, it is easier to construct special absorption cells such as coiled guides, high temperature cells, free space paths, etc.