[evlatests] ACU tests -- sky survey mode

[Rick Perley]

     You're misreading what I wrote.

     By 'overshoot', I mean that (for example) ea18 travelled six times 
too far.  That is -- instead of traversing 2 degrees, it traversed 12.  
Each antenna had a different 'overshoot' -- given apparently by its 
fringe rate.

     The cut profiles make this abundantly clear.

     It's not even clear that the 'speedy' antennas travelled in the 
right ascension line that was requested.  The 'slow' antenna show the 
expected sidelobe about -13 dB from the peak.  The 'fast' antennas show 
much lower sidelobes -- and many more of them.

     Rick

On 12/23/2014 12:32 PM, Bryan Butler wrote:
>
> the "overshoot" is expected.  an OTF "line" backs up by 1 phase center 
> from the first location for its real start position, in order to be up 
> to speed by the time it hits that first phase center.  this backed-up 
> portion is marked with a different scan intent, which you're probably 
> not picking up and flagging on.  at the end, this is almost certainly 
> just the expected overshoot from the antenna motion.  i assume by 
> "nearly six" you mean six integrations, which is 0.6 seconds.
>
> for the rest, i defer to steve & barry.  there's nothing 
> antenna-dependent in the python function portion of this - i can't 
> vouch for the executor portion.
>
>     -bryan
>
>
> Rick Perley wrote, On 12/23/14 12:10 :
>>      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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