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.
Benmessai, K., Bourgeois, P. F., Kersale, Y., Bazin, N., Tobar, M., Hartnett, J., ... Giordano, V. (2007). Frequency instability measurement system of cryogenic maser oscillator. Electronics Letters, 43(25), 1436-1437. https://doi.org/10.1049/el:20072684