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Apertif digital beamformer gets final shape

Submitter: Gijs Schoonderbeek
Description: The digital beamformer for Apertif is taking shape. It consists of eight ADUs (Analog to Digital converter Units), four UniBoard digital processing units, a PAC (Power And Clock distribution) and an AUB (ADU-to-UniBoard Backplane).

For this demonstration, three kinds of test signals simulate the signals from 64 antennas: wide-band (WB) and band-limited (BL) noise, and a CW signal of 719 MHz. The sequence of images shows what happens at the various monitoring points in the processing chain. Note that, as each image is shown, the relevant monitoring point is emphasized in the block diagram above it.

  • For the data-capture and DDR3 figures, raw samples are used. A Hanning taper is applied (in Python), prior to a 1024-point FFT. The output is plotted in a different color for each antenna input.

  • The subband statistics plot shows the power of the individual subbands at the output of the filterbank, integrated over one second. The integration is done on the UniBoard.

  • The beamformer weights are set in such a way that 42 beams are formed, with a bandwidth of 300MHz, with each beam containing one unique antenna input. The powers of the beamlets (i.e. beam-frequency combinations) are integrated for one second, and plotted in the beamlet statistics figure.

  • In total, 20 beams of a single subband are transferred to the control PC (LCU) via an Ethernet control link. On these raw beamlet outputs, a 256 point FFT is performed in Python. Subsequently, 128 of these spectra are averaged for each beamlet.

    These images demonstrate that the Apertif beamformer is getting in shape to be tested in full detail. All blocks are lined up, data is flowing as expected, and the Python scripts to control the boards are working. We look forward to an exciting period of further lab-tests, integrated with the other analog boards. This should then lead to the ultimate trials at the WRST telescope, with real celestial data!
  • Copyright: Astron
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