Frequency instability measurement system of cryogenic maser oscillator

The frequency stability measurement of a new kind of secondary frequency standard, the whispering gallery mode maser oscillator, is reported. Based on a very simple design the beatnote comparison with a state-of-the-art cryogenic sapphire resonator oscillator gave a preliminary result of 10^-14 frequency instability at 1 s integration time. The measurement is limited by the microwave synthesis chain used to evaluate the maser stability.