Receiving system for the voyager-2 neptune occultation experiment

A radio science experiment was carried out when the deep-space probe Voyager-2 travelled behind Neptune. This paper describes the receiving and recording systems which were developed for the experiment and gives a summary of the experiment itself. The object of the experiment was to detect the very small fluctuations in the phase and amplitude of the radiowave carrier as it passed through the atmosphere and rings of Neptune. To achieve this, a 64-m diameter antenna and high-performance maser amplifiers were used together and a high G/T value was obtained. The heterodyne receiver was controlled by open loops and the local signal was changed with continuous phase to match the predicted Doppler value, stabilizing the signal within the bandwidth. A local frequency generator with stable frequency and phase and a signal bandwidth filter were developed. Also, to counter antenna distortion caused by changes in the elevation angle, a method of compensation was introduced which kept the phase stable and suppressed gain reduction.