Dicke-switched receiver

Dicke-switched receiver

(dik) A radio-astronomy receiver in which the input is continuously switched between the antenna and a reference noise source of constant noise power. The switching, at a rate of between 10 and 1000 hertz, is carried out by a Dicke switch, which is typically a semiconductor-diode switch or a ferrite switch. The switching reduces the fluctuations in the output of the receiver that arise from gain changes in the amplification stages and seriously limit the performance of total-power receivers. The amplitude of the component at the switching frequency in the output of the first detector is proportional to the difference in powers between the noise source and the antenna; it is detected using a phase-sensitive detector. The effect of a change in gain is much reduced provided that the change takes place much more slowly than in one switch cycle.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006