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This article reports on the characterization of cryogenic sapphire oscillators (CSOs), and on the first test of a CSO in a real field installation, where ultimate frequency stability and continuous operation are critical issues, with no survey. Thanks to low-vibration liquid-He cryocooler design, Internet monitoring, and a significant effort of engineering,(More)
We present the characterization of 8-12 GHz whispering gallery mode resonators machined in high-quality sapphire crystals manufactured with different growth techniques. These microwave resonators are intended to constitute the frequency reference of ultra-stable Cryogenic Sapphire Oscillators. We conducted systematic tests near 4 K to determine the unloaded(More)
We present the characterization of commercial tunnel diode low-level microwave power detectors at room and cryogenic temperatures. The sensitivity as well as the output voltage noise of the tunnel diodes is measured as functions of the applied microwave power. We highlight strong variations of the diode characteristics when the applied microwave power is(More)
We present the characterization of three cryogenic sapphire oscillators (CSOs) using the three-cornered-hat method. Easily implemented with commercial components and instruments, this method reveals itself very useful to analyze the fractional frequency stability limitations of these state-of-the-art ultrastable oscillators. The best unit presents a(More)
The phase noise of a quartz crystal resonator working at liquid helium temperatures is studied. Measurement methods and the device environment are explained. The phase noise is measured for different resonance modes, excitation levels, amount of operating time, device orientations in relation to the cryocooler vibration axis, and temperatures. Stability(More)
We present a detailed characterization of two atomic clock interrogation systems based on two different cryogenic sapphire oscillators operated simultaneously. We use them as references for two accurate fountain clock frequency standards participating in international atomic time and operating both at the quantum projection noise frequency limit. The two(More)
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