Station Sample Test

Purpose

This test is intended to verify certain characteristics of the station beamformed samples. It uses the MCCS DAQ in Raw Station Beam mode, and collects two sets of data.

Requirements to Verify: i) Station Beam Data is Dual Polarisation. ii) Station Beam Data has complex samples. iii) Station Beam Data is 8 bits & has full range -127 to 127.

Sets of Data

  1. Test generators are set to slightly offset to Frequency channel 1 for Horizontal polarity, and 3 for Vertical Polarity.

    • Data is checked to only be in the expected channel for each polarity.

    • An FFT is performed for the samples to verify a peak at expected frequency.

    • (Verification procedure listed in: SKA_IF-LOW_CBF_SPS-2).

  2. Test generators are set to slightly offset to the centre of Frequency channel 5 for both polarities.

    • Data is checked to be in the expected channel only.

    • Real and Imaginary components of the samples are checked to be non 0.

    • The range of the samples is checked to be -127 to 127 for both polarities.

    • An FFT is performed on both real and complex to check the samples are sinusoid.

    • The phase lag between them is calculated and checked to be ~1/4 cycle lag.

    • (Verification procedure listed in: SKA_IF-LOW_CBF_SPS-1 & SKA_IF-LOW_CBF_SPS-3).

NOTE: The two seperate tests cannot be combined because sending a tone on a single polarity for two polarities halves the available inputs. One FPGA can output one tone to one polarity, and the other FPGA to the other polarity. (e.g. a test Generator cannot output different tones to different outputs). This means the range is less than needed for requirement iii.

Methodology

  1. Connect to the station and constrain the test start channel. Prepare scaling and truncation registers.

  2. Calculate the test generator frequencies for the different channels and polarities.

  3. Configure the Network addresses & DAQ. Ensure all ADCs or test Generators are currently disabled.

  4. Start the beamformer for 8 channels, at the chosen start channel.

  5. Enable the test Generator to output seperate tones on each polarity.

  6. Run the DAQ for ~200ms before stopping, capturing the Dual Polarity test data.

  7. Enable the test Generator to output a slightly saturated tone, the same for both polarities.

  8. Run the DAQ for ~200ms before stopping, capturing the Complex & Range test data.

  9. Evaluate Dual Polarity test. Check samples in seperate channels per polarity and only the expected channels. Check there is peak of FFT of samples at the expected frequency offset.

  10. Evaluate Data range test. Check samples have full 8 bit range & are sine waves in expected channel

  11. Stop test Generation, restart beamformer with original config then clean up.

Typical issues

Some typical issues and how they present are shown in the following table:

Segmentation Fault: Occasionally the DAQ causes a segmentation fault, causing the test to abort.