Leuschner_visit_on_6_16 - david-macmahon/wiki_convert_test GitHub Wiki

Problems with undergrad spectrometer power levels fixed

Carl and Dan made several linearity tests at Leuschner, by removing and adding 10dB attenuators at various places in the signal chain and in the noise source, and then checking to see if the power levels at various places changed appropriately in response to the attenuators inserted/removed.

Results:

  • Observations indicate that the receiver and fiber optic system is working well and linear over a large range of power levels.
  • The power levels going into the undergrad Roach-1 based spectrometer were far too high; and that system was far from linear.
  • Any previous measurements done with the undergrad spectrometer should be suspect, and all prior power and Tsys measurements done with that spectrometer (eg: using the chart recorder software...) are bogus.
  • Inserted a 30 dB attenuator in pol1, and 25 dB in pol2 , just prior to the roach1 undergrad spectrometer ADCs,

to bring the levels down to where the system behaved linearly.

Plan of action

  1. Calculate the system temperature using the data we took with the snap spectrometer with the absorber on and off (about 300K Tabsorber vs about 10K Tsky). We can't use the data from the undergrad spectrometer.
  2. Observe for few hours on PSR0329 without being aggressive about integration time (use 1 ms or more, to avoid packet loss).
    1. Do a careful search for pulses.
    2. Look carefully at the headers and parameters we are using in SIGPROC:
      1. Is the integration time parameter we enter good to six significant digits?
      2. Did we enter the correct observatory latitude and longitude? (this can mess things up)
      3. Did we enter the correct UTC and Julian date for the observation? (this can mess things up)
      4. What about all the other parameters we are using?
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