ALMA Systems Requirements Revision

Telecon notes

January 25, 2019

  • Next workshop: during developer workshop in Garching (June 3-5), maybe half-day afterward?
  • IST charged with defining tradeoff between bandwidth and sensitivity
  • Asayama presentation on technical developments at NAOJ
    • ALMA2 Project: required to insure operations budget from NAOJ continues
    • Band 7-8 combination
    • possible future 6-band approach: Iguchi et al. 2018 SPIE
  • Tan presentation on Digitizer work in EU
  • Tan presentation on System Architecture Impact:
    • Phase of (current) digitizer clock (DGCK) can be adjusted (4 GHz mixed with DDS, then mixed back) for fine delay tracking
    • Neil: time-stamping of current DTX is 8 nsec (buffer in DRX is 16 frames, dskewing function)
    • Nick: new spectrometer will use ntp server rather than 48msec tick
    • Saini: IF switch needs modification to support wider bands
    • Neil: or integrate the new switch into the digitizer itself
  • Whyborn presentation on Systems Requirements Changes Proposal
    • passband changes with input power (different loads) even when not changing the attenuators
    • ratio of IF max/min of 3 is desired
      • NOEMA:
        • The system processes 7.744GHz wide IF bands separated by 15.488GHz (= 2*7.744GHz) so the ratio of the frequencies of the upper and lower edgs of the IF band exactly meets the 3:1 ratio I discussed yesterday.
        • However, the method they have chosen to downconvert and sample the IF band in two sub-bands results in a 20MHz wide dead zone (and ~100MHz with reducd sensitivity) centred at an IF of 7.744GHz.
      • CUP2 may need to go lower than 4 GHz because clock rate is fixed (125 or 250?)
  • Line by line discussion of requirements that need revision

February 6, 2019

-- ToddHunter - 2019-01-25
Topic revision: r4 - 2019-01-27, ToddHunter
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