The main characteristics of the Microwave Source are:
- a low power spectral density of the phase fluctuations
- a frequency resolution of 10-5 Hz
- output interrogation and selection signals: 0.01 nW to 10 mW
- less than 2.10-11 sensitivity to environment on 90 mn
- an USO frequency correction via a DDS
- a synchronization signal (100 MHz/12) to the UGB
The Microwave Source is composed of an ultra-stable oscillator (USO) and a frequency synthesis chain. Thales TAS (Thales Systèmes Aéroportés) is repsonsible for the Microwave Source, and CMAC, the subcontractor of Thales TAS, for USO.
The frequency chain synthesizes two signals at 9.192631770 GHz from a 5 MHz ultra-stable quartz oscillator.
The low-noise 9.192631770 GHz output frequency is obtained from a 5 MHz reference in two steps: a phase locking of a 100 MHz VCXO and a phase locking of a 692 MHz VCO.
The microwave source has 2 direct digital synthesizers (DDS): one is used to compensate the frequency drift of the USO, the other allows a fine frequency adjustment by steps of 10-5 Hz of the 9.192631770 GHz to obtain a resolution of 10-15 of the clock frequency.
The measured power spectral density of the phase fluctuations in accordance with the Fourier frequency for the FM is:
- size: 270 x 300 x 103 mm³ (8 litres)
- weight: 7.03 kg
- power consumption: 24.5 W
The contract was awarded to Thales in 2001. The PDR has been made in 10/2001 and the CDR in 05/2004. The main deliveries were the STM in 12/2002, the EQM in 02/2004 and FM in 12/2004.
Main challenges: micro vibration sensitivity. The micro vibration impacts on Pharao Microwave Source are mainly the microwave stability degradation due to USO sensitivity to microgravity.
A LSA (Low Sensitivity to Acceleration) USO became available in 07/2005. This LSA USO replaced the FM 34 in 2006.