[evlatests] [Fwd: Band Change Timing Tests]

[Rick Perley]

With an attempt at reformatting ...

-------- Original Message --------
Subject: 	[evlatests] Band Change Timing Tests
Date: 	Wed, 17 Nov 2010 12:00:14 -0700
From: 	Rick Perley <rperley at nrao.edu>
To: 	evlatests at aoc.nrao.edu



    In preparation for a potential 'flux densities' run, I've conducted 
a pair of tests, replicating the basic methodology for (mercifully!) 
short periods.  For this, I observed 8 sources (including one planet) at 
each of 8 bands, with the goal of getting 30 seconds of good data for 
each of the 64 observations.  As all sources are strong, I can use the 
raw visibilities to judge when antennas were on source and fringing 
stably.   Observations were made in 'Extended OSRO' mode, and referenced 
pointing was done in 'OSRO1' mode. 

    The band sequence chosen was the following:

    L -> S -> C -> XRefPnt -> X -> Q -> Ka -> K -> Ku   then back to L, 
on the next source. 

    The following table gives the 'duration' time per band, the actual 
on-source stable fringe time, and some explanatory notes. 

    Band    Duration      Good Data      Notes
----------------------------------------------------------------------------------
     L    move + 50   30 --  60      Times vary for different antennas
     S        50         30
     C        75         42           Last 13 seconds of both IFpairs gave noise.
    XPnt     180                      Likely overgenerous, but the OPT insists ...
     X       90      30 (AC), 48 (BD)   Last 
18 seconds of IFPair 'AC' noise.  Another 30 seconds lost due
to  corrrelator setup (from OSRO to Extended OSRO).
     Q       50         30       10 second gap between X and Q band! 
    Ka       50         38
    K        60    48 (AC), 30 (BD)   Last 18 seconds in IFPair 'BD' is noise. 
    Ku       45         33              10 second gap between K and Ku bands!
-----------------------------------------------------------------------------------------------

   The end-of-scan noise occurs when the following observation changes 
sideband. 
    The biggest inefficiency deals with referenced pointing, especially 
having to switch modes to do this.  A test is needed to determine if 
'extended OSRO' mode referenced pointing is effective.  We should also 
test if good solutions are obtained with less than 3 minutes duration -- 
with the VLA correlator, we had good reliability with 140 seconds. 


   
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