[evlatests] ACU tests -- sky survey mode

[Rick Perley]

     Yes -- my incorrect language.  I used the 'OTF' mode in the OPT.

     I was at L-band, so the two degree travel corresponds to traversing 
from the 2nd sidelobe on one side, to the 2nd sidelobe on the other.  
The profiles for the 'slow' antennas showed they moved more-or-less as 
expected.  But only ~6 antennas did this.  All the others went faster 
(and further).

     Rick

On 12/23/2014 12:19 PM, Steven T. Myers wrote:
>
> 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               |:|
> |:| National Radio Astronomy Observatory |:|  Ph:  (575) 835-7294      
> |:|
> |:| P.O. Box O, Socorro, NM 87801        |:|  FAX: (575) 835-7027      
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> |:| http://www.aoc.nrao.edu/~smyers      |:| smyers at nrao.edu          |:|
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