iSource
®
StarLPRO-1500
Manual
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The clock microwave frequency of the Rb atoms in the vapor cell has a nominal value of 6834.684 MHz . This
frequency is generated from a voltage controlled quartz oscillator (VCXO) which is multiplied up to 60 MHz .
Multiplication from 60 MHz to 6840 MHz is accomplished in one stage (x114 ) using a step-recovery diode
mounted in the magnetron resonator inside the physics package.
Fig. 2-3: Dip minimum detection
The 5.316... MHz phase modulation is introduced at the 60 MHz level. The 5.316... MHz spectrum is thus
reproduced as a sideband of the 6840 MHz signal multiplied from the 10 MHz VCXO. The difference of the two
frequencies corresponds to the Rb clock frequency.
This 5.316... MHz is generated by a synthesizer which is frequency modulated at the rate of fm for dip
detection.
The center frequency of the synthesizer is adjustable with step sizes of 5.12uHz in order to have the capability
to adjust the STARLPRO-1500 output frequency (10 MHz ) with a resolution of 5.12 E-13 per step and, also, to
compensate the frequency shift due to the buffer gas pressure inaccuracies in the cell.
The Rb light is generated by a plasma discharge in the Rb lamp. This is sustained by an RF oscillator which
drives a coil surrounding the Rb lamp bulb. In addition, the lamp is heated to 140°C and stabilized within 0.2°C
over the full operating temperature range. The temperature controlled heating power is generated by a wound
resistive heater wire. Another part of the heating power is generated by the RF oscillator.
The Rb absorption cell is heated to ~85°C and also stabilized within 0.3°C over the full operating temperature
range. The heating by a heater wire and the temperature control follows the same pattern as for the lamp
heater.
