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

A cryocooled compensated sapphire oscillator (CSO), developed for the Cassini Ka-band Radio Science experiment, and operating in the 7 K-10 K temperature 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 than 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 indicate 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 by 20 to 28 dB over the design offset frequency range from 1 Hz to 40 Hz. Receiver design is also discussed.