Daily Image
23-04-2014
First fringes with APERTIF ALPHA-3
| Submitter: | Boudewijn Hut and Wim van Cappellen for the APERTIF team |
| Description: | In a major breakthrough, fringes have been measured with an APERTIF PAF interferometer! After the multi-year development, procurement, production, integration and testing of the ALPHA-3 system, the hardware for the first two WSRT dishes (RT4 and RT5) was recently installed. Last Friday, fringes on an astronomical source were successfully measured. This is the first time at ASTRON (and, as far as we know, the second time in the world) that an interferometer consisting of dishes with Phased Array Feeds has been built. The fringes were measured instantaneously over the full 300 MHz bandwidth. All hardware was in place, i.e. the LNA, receiver, digital beamformer, clock distribution and correlator. After testing all subsystems individually, this result demonstrates that the integrated system, from LNA to correlator, is working. The image shows the measured fringe for a single 781 kHz subband around 1400 MHz. For this experiment, two WSRT dishes on a 144 m E-W baseline were pointed at a strong astronomical source (Cas A) for a period of 300 seconds, without any delay tracking. Also shown is a measurement away from any strong source (i.e. pointing at the zenith), where the correlation should be negligible, or rather noise-like. The measured variance of the correlation coefficients is indeed as expected, i.e. 1/(Bt). Until now, only single-dish measurements and correlations between an MFFE and a PAF have been performed. The present PAF interferometer allows us to characterize the APERTIF system at a deeper level. Specifications like bandpass stability and RFI immunity can now be validated with representative hardware and at the desired accuracy. |
| Copyright: | ASTRON, 2014 |
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