TGBT14A_912_69 - continued bank discrepancy tests on real VEGAS


  • Start 8:10am
  • run into Manager problems (loading old BOF). Finally get started around 10:30am.
  • This BOF seems to have too much fixed digital gain, causing filtersnap_nogain to clip
  • setting input power to -28dBm causes filtersnap_nogain power to be -12dBm, just beginning to hit +/- 127.
  • Deduce we want 16dB less fixed digital gain. We have to do powers of three, so select 15 dB less gain.
  • Randy goes off to build a new BOF file; stop testing for now.

  • Start again with BOF 119 at 1:45pm
  • Now input power of -28dBm causes filtersnap_nogain to be -30dBm. We seem to have lost 26dB of gain!
  • digital gain seems to need to be around 2**26.3, or 90000000. Keep it fixed at this value throughout the test.
  • various scans to check the procedure is correct.
  • run checkLinearityBalance, with a VEGAS balance to get CM rack, but then lbw_gain set to 90000000.
  • run over target ranges (-36, -6, 2), start with Scan 3
  • Note: VEGAS doesn't seem to balance as good as +/- 2dB (as in the spec)
  • e.g. target -32 gives: -32/35, -32/32, -28/28, -34/34.
  • for target of -10dBm, CM13 and 14 fail, but BankE is the one that looks off.
  • But converter racks are running out of attenuation here. Also, filtersnap is also clipping.
  • Finishes with scan 17
  • Note: they have changed from KFPA to L-band! Run the test again with L-band configured.
  • Now using Banks A,B,C,D
  • Run checkLinearityBalance again, (-36,-6,2)
  • starts with scan 18
  • These numbers seem even more bogus - looks like KFPA was in focus after all (despite Antenna Monitor screen).
  • Now seems like we need a lbw_gain of around 2**25 = 33554432
  • revert to old system. For many attempts, VEGAS will not balance, but then fixes itself. Very wierd!!!!
  • Scan 33 - eso558_vegas just to do a test scan - looks fine.

-- RichardPrestage - 2015-02-10
Topic revision: r4 - 2015-02-10, RichardPrestage
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