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Description: | Radio telescope receiver for 33.5 GHz. Large aluminium box divided by a hexagonal sheet of metal . On the front is a screen with a scale from 0 to 10 mA, four brass microwave inputs/outputs and six electrical tsockets. Inside the box is a large round brown object labelled 'Decca', a ferrite switch and several microwave units, a temperature controller, an IF LF mixer P.S., a BIAS, a fan (mounted on the hexagonal sheet which divides the microwave section from the low frequency section) and a lot of wires!. Two sides are open, enabling us to see inside. Designed and commissioned in the mid 1970s by the Natural Philosophy radio astronomy group under Dr Alistair Flett. For an extensive description of the design see chapter 2 (pp 5-51) of the PhD thesis of Stephen J. Drake "9 mm wavelength observations at the Chilbolton Observatory" (1977). Figs 2a-d are photographs with identification of the elements of the receiver. The box contains two microwave receivers. The main one is a 2-channel superhet with no microwave amplification. The first stage is a balanced mixer using GaAS Schottky barrier diodes in waveguide wafers. The local oscillator is provided by a Plessey Gunn effect diode in a tunable cavity. The balanced mixer outputs are 190 degrees out of phase and are fed into a 3-stage Avantek IF amplifier givein 3x16dB gain over the flat band 100-500 mHz. The output is fed to a square-law dettector (o/p voltage is proportional to input power) and amplifier giving 8 mV/microwatt and then into a further LF amplifier. The receiver includes Dicke switching and phase sensitive detection. There is an interanl heater so that the device can operate at a steady 310 K to stabilise the amplification. A second receiver was added over October-November 1975 to the design of Dr John C S Richards and Dr Patricia R. Foster so that the device could operate with a single channel input and a stabilised comparison load. The Decca switch belongs to this second receiver. The RMS expected noise performance is reported as 0.15 K. Astronomical microwave sourcesof interrest had temperatures about 10 K. The box was built in the Nat. Phil. workshops in 1974 and 1975. The group operated with their own parabolic dish located at Hillbrae, some 6 miles north of Aberdeen and, later, at Chilbolton Research Station in Hampshire where this receiver was used.. Results are reported in Stephen Drake's thesis. | License: | http://www.abdn.ac.uk/historic/Copyright_terms_conditions.shtml | Publisher: | ABDNP University of Aberdeen, Natural Philosophy Collection of Historical Scientific Instruments | Rights holder: | 47718 | Temporal: | 1974-1975 | Source: | University of Aberdeen | Identifier: | http://calms.abdn.ac.uk/Geology/dserve.e... | Go to resource |
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Amplifier
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