Limitation of Gravitational Wave Detector Niobe Sensitivity by the Frequency Tracking Noise

The gravity wave detector at the University of Western Australia was based on a bending flap of 0.45 kg tuned near the fundamental resonant frequency of a 1.5 ton resonant-bar of 710 Hz at a temperature of 5 K. The displacement of the bending flap was monitored with a 9.5 GHz superconducting re-entrant cavity transducer. The performance of the transducer is related to the development of a low noise microwave pump oscillator to drive the transducer. This work studies the influence of the frequency tracking noise of Niobe. It had a burst sensitivity of h approximate to 7 x 10(-19) with a long term operation from 1993 to early 1998. It had the lowest observed noise temperature. Using the characteristics of the detector, NIOBE should had reached a much better sensitivity that the one measure. It seems that the noise introduced in the system by the frequency tracking device was not taken into account at the time of operation, this noise gives a value of approximate to 2.5 x 10(-18) m/(Hz)(-1/2), what is the value that limited the detector sensitivity to the one measured at the time of operation.