A cooled UHF receiving system for radio astronomy

Abstract

The 250 ft (76 m) Lovell radio telescope at Jodrell Bank has been a familiar feature on the Cheshire landscape for nearly forty years and throughout this time it has been a scientific instrument of tremendous value in radio astronomy research. This includes spectral line observations (allowing scientists to investigate the chemistry of the Universe), mapping of distant objects (up to the edge of the observable Universe) as part of the MERLIN network, and observation of pulsars, rapidly rotating neutron stars which emit sharp beams of radiation much like stellar `lighthouses'. Receiver sensitivity is of paramount importance in this work, as the `signals' of interest are weak in the extreme. In order to achieve the best possible sensitivity engineers at Jodrell Bank are using closed-cycle helium refrigerators to cool receivers to around 15 K. Hitherto such cooling techniques have been restricted to receivers operating at L-band and above. Pressure from astronomers, particularly those searching for pulsars, for greater sensitivity has led to the development of a dual frequency UHF cooled receiver front-end covering the radio astronomy bands nominally at 408 MHz and 610 MHz.