UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS

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2024-11-22 2:24
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Conference: Bucharest University Faculty of Physics 2005 Meeting


Section: Electricity and Biophysics


Title:
Fast Modulation of the Cavity’s Resonant Frequency for the Passive Hydrogen Maser


Authors:
Claudiu Mirica, Liviu Giurgiu, Octav Gheorghiu


Affiliation:
INLPR Bucuresti-Magurele


E-mail
octavgheorghiu@yahoo.com


Keywords:
Atomic Clock


Abstract:
The passive Hydrogen Maser resonator is a microwave cavity that has couplings with the in- and output circuits, and with the confined atomic oscillator within the cavity. The detected physical quantity is the output voltage of the cavity. In the passive detection of the atomic resonance an operating parameter is modulated to extract the information through synchronous detection. The most used technique is the fast modulation of the interrogation frequency. This work studies the possibility to use a fast modulation of the cavity’s resonant frequency through the tuning Varicap diode. While keeping the interrogation signal unmodulated, the output signal has harmonics of the modulation frequency. This harmonics have amplitudes that depend on how much is modulated the cavity’s resonant frequency. The calculations show that the useful signal is maximized if both the frequency and the amplitude of the cavity resonant frequency modulation are equal to the half-band width of the loaded cavity. Also, the superior harmonics of the signal are filtered by the cavity, leaving only the carrier and the first harmonics of the modulation. The carrier is resonant with the atomic oscillator and its dispersion changes the phase of the harmonics through the modulation. Also, the cavity tuning changes the harmonics amplitudes. By linear detection, the amplitude modulation of the signal is synchronously detected in a similar way as in the fast frequency modulation technique. An advantage of this technique would be that the resonant carrier dispersion by the atomic oscillator is present in the amplitude modulation not by the square detection of the signal, but by the parametric modulation itself.