[mmaimcal] Q-band on ALMA

[Min Yun]

Steve,

> Indeed, I made this case to Stephane, but he insisted that this was not
> the case and 86 GHz would be useable essentially all of the time, claiming
> that this is what the found at IRAM.  We will need to carefully document
> this - probably should base it on the data from Devlin's MAT experiment
> (which observed at Ka/Q/W bands) as well as the site testing info.
The longest baseline at PdB is still only a few hundred meters, and
they are also helped by their total power phase correction system.
I rarely experienced any weather short of rain and snow storms that
prevented 90 GHz observations at OVRO, but the situation
reversed once we went to the "ultra-high" configuration with 400-m
baselines -- decorrelation was not too severe only during limited times.
I am guessing that what Mark calls "hopeless 
conditions" are when even the phase correction schemes will not
help, presumably for some limiting baselines or configurations.

> Also, is anyone else even a little concerned about putting all the
> receivers in a single (4K) dewar?  It might be good to have a second
> 15 K dewar with 30-45 GHz band and maybe the 86+ GHz band also.  This
> would ameliorate some of the percieved extra costs associated with
> the Ka/Q band stuff.
> 
> By the way, the project book has 67 - 90 GHz and 89 - 116 GHz bands,
> in which case the 67 - 90 is a likely candidate for HFET/MMIC tech.
> Is this still in the plan, or like the rest of the project book is
> this horribly out of date?
This issue has been addressed in reverse for the most part of the
project.  Having a single dewar has been cited as an advantage by
the cryo group, and therefore the Q band system which requires a
separate dewar must go.  Not using HFET/MMIC for the low freq.
was also driven for a similar simplicity argument.  This is not to
say I agree with these reasoning, but I wanted to bring you up to
date.  It may be worth revising as part of having a separate dewar
for the Q-band system.





					-- Min