[mmaimcal] Vertex Antenna turn around time

[Mark Holdaway]

> Hi Folks,
> 
> I have been looking into this issue of the current Vertex design
> performance for maximum slew rate turn around time.  Recall that the
> current design indicates a turn around time of 0.8 seconds assuming a
> 30'/sec scan rate and a scan time of >2 seconds in OTF mode.  Note
> that this implies a >1 degree scan length at the maximum rate.  I have
> reviewed this issue with Mark Holdaway, where the basis for the
> discussion relied on Mark's unpublished memo on a comparison of beam
> switching and OTF for continuum total power measurements.  From that
> work, Mark found that OTF total power observing is as good as or
> better than beam switching for optimal sky subtraction when one could
> OTF map at the maximum slew rate (1 deg/s) and a 0.2 second turn
> around time.  So, Vertex is within a factor of 8 of meeting Mark's
> simulated break-even point.
> 

factor of 4?

> If we assume that all antennas will have nutators, then the current
> performance will not be a problem.  Note also that we will not be able
> to resolve this issue of whether fast OTF gives us the same capability
> for sky subtraction as nutators on the prototype antennas, so if we
> ask Vertex to do better, we have no way of testing whether this was
> necessary.  So, given all of this, I am inclined to say that the
> current fast motion performance is ok.
> 
> Any comments?
> 
> Cheers,
> 
> Jeff
>