[mmaimcal]Phase Repeatability of the Attenuators

[Bryan Butler]

the spec on frequency switching of the LO is currently 1.5 sec.
this from larry's chapter 7 of the project book, page 3.  my
vague recollection was that it was even longer, but there is the
confusion of whether it is one of the currently 'warm' cartridges
in the dewar.  there can be 2 'warm' cartridges, and if you switch
between only them, then i think that is when the 1.5 sec spec
applies.  this is OK for most fast-switching observations, since
folks will just be switching between 90 GHz and their frequency of
interest.  those who want to do multi-frequency observations will
have to figure out a different way of scheduling it though, since
it will take longer to warm up the 3rd (or more) frequency
cartridge.

larry can correct me if i'm wrong here.  i usually am, it seems,
whenever i try to quote something of this nature...

so, mark, you should account for at least 1.5 sec *between* the
observations (this does not count on-source time, of course) in
fast-switching - this should account for most of the antenna
mechanical settling, and the LO settling.


	-bryan


On 2002.08.07 11:31 Mark Holdaway wrote:
> 
> > 
> > i think you've got the timescales too short here.  isn't the limit
> > on switching bands something like 5-10 seconds (larry, correct me
> > if i'm wrong here)?  certainly the settle time is more than 1 second,
> > so you'll have to have many seconds on calibrator, and some multiple
> > of that on source.
> 
> I believe 1.5 seconds is stated.   If it is 10 seconds, there is
> little point in fast switching.
> 
> BTW:  Darrel points out that the attenuator's phase won't scale with
> frequency, which means
> 
> 	* we MUST measure it (and other phase components
> 	which don't scale)independently of the fast switching
> 	observations and make a note of it and apply those phases
> 	before scaling the 90 GHz cal phase
> 
> 	* the applicable number is more like 6.4 deg  (though
> 	if this is the case, I would be more stringent and
> 	say sqrt(16^2 - 15^2) = 5.5
> 
> 	-M
> 
> 
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