A phase-stabilized local-oscillator system for a synthesis radio telescope

A system is described which delivers signals of precisely controllable frequency and phase to remote points. The system is used to provide local-oscillator signals at widely separated antennas in a synthesis radio telescope operating at 1.4 GHz. Phase accuracy is 1.1° rms. The system is a closed-loop phase-control circuit employing phase-locked loops. A reference signal is supplied to the system, and the phase of an oscillator at the remote location is tied to this reference. A single coaxial cable joins the central and remote components of the system. Feedback is employed to render the phase of the remote oscillator independent of the length of this cable. A detailed analysis of the sideband generators used in the system is presented. Analysis of overall system dynamics shows that stability is easily achieved and is not impaired by the time delay of the transmission path to the remote unit.