In this paper, we report the development of the design
verification model (DVM) of Rb atomic frequency standard for the Indian
Regional Navigational Satellite System (IRNSS) programme. Rb atomic clock is
preferred for the space applications as it is light-weight and small in
size with excellent frequency stability for the short and medium term. It has
been used in all other similar navigation satellite systems including GPS,
GLONASS Galileo etc. The Rb atomic frequency standard or clock has two distinct
parts. One is the physics package where the hyperfine transitions produce the
clock signal in the integrated filter cell or separate filter cell
configuration and the other is the electronic circuits which include frequency
synthesizer for generating the resonant microwave hyperfine frequency, phase
modulator and phase sensitive detector. In this paper, the details of the
Rb physics package and the electronic circuits are given. The reasons for the
mode change in Rb lamp have been revisited. The effect of putting the photo
detector inside the microwave cavity is studied and reported with its effect on
the resonance signal profile. The Rb clock frequency stability measurements
have also been discussed.
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