A New 9-GHz Synthesis Chain for Atomic Fountain Clocks

We describe a new microwave synthesizer chain to produce the 9.192 GHz Cs frequency currently being developed in a cooperation of PTB and NPL India. In this synthesis a 9600 GHz YIG oscillator is locked to a 5 MHz quartz oscillator via a divider chain (9600 : 8 : 3 : 4 : 20). Along the way, a signal of 407.37 MHz is generated with the help of direct digital synthesis (DDS). The required interrogation frequency is obtained by mixing (9600 MHz - 407.37 MHz = 9192.63 MHz). The signal from the atoms is then used to steer the 5 MHz quartz frequency. We discuss the preliminary results of studies of the metrological features - namely, the spectral purity, phase noise and the long term phase stability -of the few prototype units constructed so far.