7.5: Direct IF sampling of TWT AM and PM noise

The development of a novel technique for measuring TWT AM and PM noise is reported. The new method utilizes a dual channel microwave downconverter and a 16-bit high-speed digitizer to directly sample the IF allowing digital demodulation of AM and PM noise simultaneously. A prototype AM/PM noise measurement system has been built with a measurement single-sideband noise floor of -155 dBc/Hz at 100 kHz offset from the carrier.