====== ROACH2 Signal Levelling ======

The power input to the ROACH2s can be controlled by the Raspberry Pi integrated in to the gain box. A feedback on the power levels are only possible by consulting the output of the ROACH2 ADCs (either ADC histograms or the output of the PFB-FFT). This of course will only be possible if the ROACH2 FPGA is programmed appropriately, or configured with the right gateware.

  - connect to the VNC session asterix:4 (use CrabPulsar to connect).
  - load a firmware that has some ADC interfaces. eg. ''python /home/pulsar/roach2/NewFirmware/r3xsetup_new.py''
  - start the ADC displays now: ''python /home/pulsar/roach2/NewFirmware/r3xadchist_new.py''
  - Now change the attenuator setting from another terminal: ''roach2attn <id> <atten>'', where id is 1,2,3 or 4, and attenuation is in the range of 0.5-30.5 dB in steps of 0.5. See example in the screen shot below.
  - Consult the setting on the histogram above - aim to get the signal between -50 to +50. You should see something similar to the plot in the image below.
  - For Galactic Centre magnetar observations, current settings are: 18.5/15.5/12.5/6.5 dB
  - For normal pulsar observations: 9.5/7.5/6.5/2.5
  - Refer to the image below for an example display.

{{ :pulsarinstruments:gain_ctrl.png?300|}}