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B.12. Changing to 1MHz Zooms

Note: This is really for experts - if you haven't been trained for it, don't try it!

To change modes it is necessary to:

  • stop the current scan

  • cccversion: 1MHz mode works in either standard version

    To check the cccversion: caccc> cccversion. Standard versions are “newzmsy” and “VLBItwommlos”.

  • in cacor, open the edit menu

    select the edit button in the cacor gui,

    • select the 1MHz zoom config

      edit> get ca_2048_2048_2f_zm16

    • and program the correlator

      edit> prog

      Check that all blocks program correctly. If any blocks report an error, they need to be programmed again, e.g.:

      edit> prog 8 or edit> prog 8 27

    • <CR> to return out of the edit menu

  • Calbands should be the default as this happens automatically whenever you exit from the edit menu. This is what you need for this config.

  • start observing a strong calibrator, e.g.

    caobs> track 1

    Note: Wz16_cb16_5500 is a zoom schedule file with a set of calibrators for setting up.

  • Check for rear transition module (rtm) problems

    F1 and F2 Datalinks (separate tabs in the CACOR gui) should not have red error messages, and the 1ms values are in the range 2000 - 13000 (i.e. not 260 000). Fix with:

    cacor> rtminit (e.g. cacor> rtminit ca03 2a)

  • Check (in spd) for “big humps”

    To fix, reprogram the relevant block. To determine the block, note antenna, frequency (1 or 2), and polarization (A or B) - then read off the block from the relevant Datalink tab on the CABB GUI.

  • #Check (in spd - look at the zoom autocorrelations) for “small humps”. To fix, reprogram the relevant block.

  • Still looking at the autocorrelation continuum spectrums, check for spikes.

    Use differences:

    spd> rsave Saves every cycle into a reference so that you display a running difference of the current cycle against previous cycle.

    spd> d -100 100 To actually see the difference

    Note:You need to wait several cycles after a reprogram until you are actually getting a relevant difference.

    To fix, work out which block is involved with the where command:

    cacor> where zoom f# channel#

    (e.g.cacor> where channel f1 430 returns the block that is correlating channel 430 in IF1)

    Program block with:

    edit> prog # calc

    Iterate until all spikes are cleaned up

    Note:There are problems with block 8 and 28 which mean that the autocorrelations on CA03 are never really clean

  • When ok, calibrate the delays [dcal]

    Still in autocorrelation, difference mode, look for spikes and blocks of bad data in z1 and z2. Identify any offending blocks using the where command.

  • To reprogramming a block:

    config> prog [offending block] calc or

    config> prog [offending block] x 7,8 or

    config> prog [offending block]

    Note: calc resets the c bus; x 7,8 resets CABB board memory controllers; and No swith will reprogram the whole block, (delays need to be recalculated)

  • Iterate until all is good

  • Now that the autocorrelations are done, time for the cross correlations. Again, check (in spd) which channels are causing problems, and determine (from where) which blocks need reprogramming - and program again

    Iterate again

  • And finally (well almost finally) the cross products

    Set this up with:

    spd> on ab ba

    spd> sel *

    Look for spikes

    You can't do much about a single spike - but average for 20-30 cycles and look for a rash of spikes

    And again, determine (from where) which blocks need reprogramming - and program again.

    Iterate!

  • And finally (finally) check (in vis) that the amplitudes are stable over time. Determine which antenna/frequency/polarisation are unstable, and reprogram the block indicated by the datalink tabs in CACOR

    Then, the observer comes along with a different zoom setup from what you have set up with and problems may occur. So, try to get hold of their schedule and check that it still works.

  • Setup standard flagging

    cacor> fflag f1 birdies

    cacor> fflag f2 birdies

    NOTE: all flagging is cleared every time you exit from the edit menu

  • Check (in spd) baseline amplitudes and phases

  • Check that tvch is set to appropriate values

  • Check that delavg is set to an appropriate value

  • Standard setup follows (i.e. dcal, acal, pcal etc.)