[evlatests] ACU tests -- sky survey mode

[Steven T. Myers]

I take it you used the OTF mode in the OPT (or is this a different mode)?

This is alarming. Ive seen things like this in my tests, but only at the
~0.5sec level, and not with a discernable pattern. Certainly nothing like this.

What band were you at?

I will come see you about this.

-s

On Tue, 23 Dec 2014, Rick Perley wrote:

>    I've been asked to continue testing of the new ACU-equipped antennas, 
> using the new 'sky survey' modes.  These allow one to speed through a 
> specified part of the sky at different rates.
>
>    An initial test was run yesterday.  For this initial test, I picked two 
> positions:  the first one (true) degree east of 3C48, the other one degree 
> west of 3C48.    Six 'cuts' were specified, each traversing the two degree 
> separation.   The idea was to get a nice cut through the primary beam, 
> roughly from the 2nd null on one side to the second null on the other.  They 
> specified cuts were:
>
>    1) West side to East side in 4 minutes.  This is twice the 'sidereal' 
> rate.
>     2) East side to West side in 4 minutes.         ditto
>     3) West side to East side in 2 minutes.   This is 4X sidereal
>     4) East side to West side in 2 minutes.           ditto
>     5) West side to East side in 1 minute.    This is 8X sidereal
>     6) East side to west side in 1 minute.             ditto
>
>    Averaging time was set to 0.1 seconds.  For each of these six cuts, I 
> specified 100 phase steps.  So, for the first two cuts, the number of 
> integrations per phase step was 24.  For the next two, 12, and for the last 
> two, 6 integrations/step.
>
>    The results were *completely* different than expected.
>
>    Each antenna moved at a different rate!  The only antennas which traveled 
> at close to the specified rates were ea04, 06, 15, 17, 20, 22, and 28.  Some 
> antennas zipped through the pattern at many, many times the specified rate. 
> The most extreme example was ea18, which went through the pattern at about 
> six times the specified rate. This 'amplification' factor was the same for 
> all five completed cuts.  (For reasons unknown, the last cut was not 
> executed).
>
>    Furthermore, the profiles show that only the 'slow' antennas with smooth 
> motion. The faster the cut, the more jagged the profile.  The fastest ones 
> are actually in big steps -- looking rather like holography mode!
>
>    It's easy to find the basic relation -- the antenna motion amplification 
> is a factor of the fringe rate!  The target source was rising over the west 
> arm -- elevation = 50 degrees, at which point the motion is almost entirely 
> in elevation.  Fringe rates are high for the west arm, and low for the 
> others.  All the 'fast' antennas were on the west arm -- the further out the 
> arm, the faster the antenna moved (and the more steplike).  All the 'slow' 
> antennas were near the center of the array, on the E and N arms.
>    Examination of the cuts show that the antennas did not start and stop at 
> the specified points, but overshot -- on both ends by a factor of up to 
> nearly six.
>
>    So something is clearly not right here.  I don't think I did any illegal 
> in the setup (the OPT is really simple for this mode).  But clearly it's not 
> working in any sensible manner.
>
>
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|:| Steven T. Myers                      |:|  Astronomer               |:|
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