Stability and phase noise tests of two cryo-cooled sapphire oscillators

A cryocooled compensated sapphire oscillator (CSO), developed for the Cassi ni Ka-band Radio Science experiment, and operating in the 7 K-10 K temperat ure range, was demonstrated to show ultra-high stability of sigma(y) = 2.5 X 10(-15) for measuring times 200 seconds less than or equal to tau less th an or equal to 600 seconds using a hydrogen maser as a reference. CSO-1 and CSO-3 are now both operational with new low noise receivers. We have made initial phase noise and Allan deviation measurements that show more than 10 times stability improvement over the hydrogen maser for measuring times 1 second less than or equal to tau less than or equal to 10 seconds, and indi cate performance for the individual units of sigma(y) approximate to 3 x 10 (-15) for measuring times from 10 to 1000 seconds. Phase noise is reduced b y 20 to 28 dB over the design offset frequency range from 1 Hz to 40 Hz. Re ceiver design is also discussed.