Microwave noise source modulator and power supply

Low pressure gas discharge tubes and some types of commercial fluorescent lamps make excellent secondary standards of microwave power,' generating spectrally "white" noise at a level of about 15 db above ambient thermal noise. The noise output, in addition, is not critically dependent on the discharge current, The operation of certain types of noise measuring circuits requires square-wave modulation of the discharge tube. The circuit described here can operate either continuously or square-wave modulated, any commercial noise-source tube operating at currents less than 250 ma. It provides 60-cycle square-wave modulation by means of an internal relay; the relay may also be operated from an external synchronizing source, at somewhat different modulation frequencies.