[mmaimcal] Re: [alma-sw-ssr] question about frequency/band switching speeds and rates

[Darrel Emerson]

I believe Robert Lucas is working on the details, but I don't think
we want to track the phase centers as such as they move across
the sky with the primary beam in OTF interferometry.
If you do that, you end up with artificially high fringe rates that
are too high to sample - Larry pointed this out.  However, if
you keep the phase center more or less fixed, but track the fringe
frequency rather than its absolute phase, that's a more slowly
changing quantity across the sky, & it becomes manageable.
Of course you do need to track the delay center with the primary
beam, but not necessarily the phase center.

   There was some discussion on this issue a couple of years back.

              Cheers,
                    Darrel.

Bryan Butler wrote:

> 
> 
> On 2/3/05 22:45, Bryan Butler wrote:
> 
>>
>> . OTF mosaic cell phase-center saltation: rate=100 usec; speed=10
>>   usec.
>>   [for the rate, i've assumed slewing at 1 deg/sec, and 950 GHz,
>>   with 2 samples per FWHM; speed is a guess - it will depend on
>>   how fast the correlator can reset delays]
> 
> 
> OK - got this one totally wrong.  slew rate for OTF interferometry is 
> 3'/sec, not 1d/sec, which corresponds to 15 msec required 
> reconfiguration speed if the phase centers are changed discretely as the 
> antennas slew across the source...  but it's not clear this can be 
> accomplished if the correlator phase center can only be updated on 48 
> msec boundaries?
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