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22GHz receiver first light on 26-m telescope 2007/02/01

The 22GHz receiver passed its final bench tests and calibration and was installed on the 26-m radio telescope on 2007 February 01. The receiver is a "low cost" uncooled, single-feed, dual-polarization system.

Jupiter was chosen as a bright, compact test radio source. The first scans across the planet showed the expected signal were taken at exactly noon, and are shown below. The arrival of a thunderstorm prevented further testing for the day.

Reduction of the data from the first scans suggest that the aperture efficiency was approximately 27%. Further calibration will be carried out.

The detection of Jupiter vindicates the resources spent on the upgrade of the 26-m telescope with a new reflecting surface that was completed in 2004. The telecope was originally built with an aluminium mesh surface and operated at a frequency of 960 MHz, equivalent to a wavelength of 30cm. It can now operate at wavelengths from 18cm to 1.3cm. Previously the shortest wavelength at which it could operate was 2.5cm.

The measured efficiency implies that the new surface has a roughness of less than 1 millimeter, over an area of 527 square meters.

22GHz rcvr
Left click on image for large version.

The picture above shows the receiver in final assembly in the microwave workshop.


The first scan across Jupiter. The signal from Jupiter appears as the "bump" in the centre. Jupiter is much smaller than the width of the beam, so the width of the "bump" really shows the width of the main beam, which is about two minutes of arc, or 1/30 of a degree. The upper graph shows the left circularly polarized signal, the lower shows the right circularly polarized signal.

Hart sunset
Left click on image for large version. credit: M Gaylard / HartRAO

After a pretty sunset, the Orion region came into view.

Orion KL H2O

The Orion KL nebula provided the target for the first ever spectrum of a water vapour maser obtained by a radio telescope in Africa.

This pointing test was followed by the spectrum shown above. The spikes in the middle are the maser emission peaks. The instrumental bandpass of the spectrometer and its filters provides the broad pedestal on which they sit. The bandwidth used was 8 MHz, and the integration time was 20 seconds.


The next morning, clear weather permitted better measurements of Jupiter near zenith meridian transit. Orthogonal scans are shown above. The green scans are the first pair, and the red scans are the second pair, after application of pointing corrections to centre Jupiter in the beam. The signal is nearly twice as strong as in the original observation, and the baseline is much flatter.

Adopting a brightness temperature for Jupiter of 140K, the infered aperture efficiency near zenith is better than 40 percent. This implies the surface error near zenith is about 0.5 mm. This is consistent with what was estimated when the antenna surface panels were aligned in 2004 September.