Re: [alma-sw-ssr] Pipeline Requirements new version

[Bryan Butler <bbutler@nrao.edu>]

On 2001.08.30 09:34 Mark Holdaway wrote:
> 
> Mel wrote:
>
> > 2. At high frequencies, a suitable monitoring source
> > may be found in the offset beam corresponding
> > to a low frequency band. These
> > offset beams move w.r.t. the target source, so the
> > monitoring source will change with time, but one
> > is only interested the phase, not the source.
> > The simultaneous observation of the target at
> > high frequency and a monitoring source in an offset beam
> > at low frequency  requires  a few things, like
> > 2 active receivers, sharing bandwidth and correlator,
> > but has the advantage of a continuous phase calibration
> > on a nearby source.
> 
> I think dual frequency observations have been ruled out by the systems
> group.
> 

i agree with mark here - simultaneous dual-frequency operation has
been completely ruled out (if you don't count the WVR).  i'm pretty
sure we are beyond the point at which this decision can be changed.
the current design is that there is one 'hot' receiver - i.e., the
one currently being used; there is one 'warm' receiver, which can
be switched to on short timescales (1 sec or so, i think is the
spec) - i.e., the low frequency Rx for fast switching calibration;
and one which is 'ready to be warmed up' - i.e., the next observing
frequency (it takes 10 or 15 secs for this to be ready, IIRC).

note that we are seriously considering this kind of a calibration
scheme for the EVLA, where all of the receivers are 'on' all of the
time.  there are some difficulties with transferring the phase, but
it certainly looks promising.

	-bryan