Frequency-temperature dependence of an WGE mode, measured by beating against another CSO and logging the difference frequency as the temperature of one sapphire resonator is ramped.
Schematic diagram showing design features of the lower portion of the helium Dewar insert comprising two vacuum cans and the sapphire loaded cavity.
Schematic diagram of a CSO showing three control systems stabilizing its frequency and power and eliminating the spurious amplitude modulation of the interrogation signal. Thick lines indicate microwave coaxial cables. controlled pahse shifter, controlled attenuator, pass filter.
Schematic diagram of a CSO with an external Pound FD illustrating the technique used for evaluation of the clock’s frequency stability due to intrinsic fluctuations in the frequency discriminator.
Curve 1 is the Allan frequency deviation of a free-running oscillator. Curve 2 is the FD noise floor calculated from voltage noise measurements.
Noise suppression factor of the frequency control system curve 1: approximation obtained from the ratio of two phase noise spectra; curve 2: calculated dependence for the integrator based feedback loop.
Calculated spectral densities of phase fluctuations of both a free-running and a frequency stabilized CSOs, along with the phase noise floor of the Pound FD.
Frequency-to-voltage conversion efficiency of the Pound FD as a function of incident power: curve 1 , curve 2 , and curve 3 . The following list of parameters was assumed: , , , a resonator coupling coefficient , and a -factor of .
Optimized frequency-to-voltage conversion efficiency of the Pound FD as a function of incident power: curve 1 (, ), curve 2 (, ).
Schematic diagram of the interferometric Pound FD.
Inferred fractional-frequency stability from voltage fluctuations due to amplitude modulation of the interrogation signal. Curve 1: modulation signal on (bias control loop open). Curve 2: modulation signal off (bias control loop open).
Experimental setup for the in situ evaluation of the frequency stability of the CSO due to amplitude fluctuations of the interrogation signal. The digital voltmeter (DVM) and a personal computer are used to compute the square root Allan variance (SRAV) of fractional voltage fluctuations at the output of the additional channel of the measurement system.
Measured Allan deviation for a single oscillator from the beat between two nominally identical cryogenic sapphire oscillators (curve 3: gate time of ) and between one cryogenic sapphire oscillator and a hydrogen maser (curve 1: gate time of ; curve 2: gate time of ) to determine the long-term performance.
Measured Allan deviation for a single oscillator from the beat between two nominally identical cryogenic sapphire oscillators. One oscillator acted as a reference oscillator with all control systems operational. In the second oscillator power control and AM-index suppression was turned off (curve 1: gate time ), power control on, and AM-index off (curve 2: gate time of ) and both power control and AM-index suppression on (curve 3: gate time of ).
Relative beat note between a cryogenic sapphire oscillator and a synthesized signal from an environmentally isolated and temperature controlled hydrogen maser, measured over by using a countergate time of .
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