1 An electronic device that detects and amplifies radio signals captured by an antenna. Receivers used in radio astronomy are generally similar in principle to those used for other purposes, such as a domestic radio, although they are usually cooled to near absolute zero to reduce thermal noise and hence increase their sensitivity. On radio telescopes the incoming signal, after amplification, is mixed with a local oscillator to produce a lower intermediate frequency that suffers lower loss when passing along cables from the telescope to the observing laboratories. This is sometimes termed a superheterodyne receiver. See also Dicke Radiometer.
2 The equipment used to process signals received by a radio telescope. There are three main types: line receivers are used to observe spectral lines, where high stability is required together with the ability to scan in frequency or to observe at several closely spaced frequencies; continuum receivers are used for carrying out radio source surveys at a wide band of frequencies; and timing receivers are used to measure the arrival times of the radio pulses emitted by pulsars. See also Correlation Receiver.
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