A measurement of the period stability of a free pendulum in vacuum

High period stabilities can be expected of a fiber suspended light pendulum swinging freely in vacuum, mainly because of the extremely high Q factors (>10/sup 5/) obtainable in this almost frictionless mechanical oscillator. In this paper, the modelization and the projected stability limitations of such a system are discussed. Both the physical arrangements and the electronic data collection solutions adopted in the experimental realization of a prototype pendulum apparatus are described, and sample series of period measurements are reported, analyzed and discussed. Mechanical instrumental noise (no isolation against vibrations was provided) appears to limit the Allan deviation of post modelization residuals with a white noise of a few /spl mu/s per period, which masks all projected period measurement stability limitations. It is argued that this observed noise is generated by instability in the position of the period detector, and possible solutions to this problem are proposed.