[mmaimcal]Re: [Almacal] memo 372 review reply - gurwell

[David Woody]

My phrasing came out wrong (that is the problem with trying to
get this stuff out quickly with minimum effort).
What I should have said is that the power you measure is just
the system noise, thus if you get Vsky volts on the A/D after your
power detector then your gain is Vsky/Tsys [Volts/Kelvin].

I will wait for Larry's description of exactly what he proposes
before commenting on ALC vs. no ALC in the system.

********************************************
| David Woody
| Assistant Director of Instrumentation
| Owens Valley Radio Observatory
| Caltech
| P.O. Box 968, Big Pine, CA 93513
| phone 760-938-2075ext111
| dwoody at ovro.caltech.edu
********************************************
----- Original Message -----
From: "Larry D'Addario" <ldaddari at tuc.nrao.edu>
To: "David Woody" <dwoody at ovro.caltech.edu>
Cc: "Larry D'Addario" <ldaddari at tuc.nrao.edu>; "Bryan Butler"
<bbutler at aoc.nrao.edu>; <almacal at cv3.cv.nrao.edu>; <awootten at nrao.edu>;
<bbutler at zia.aoc.nrao.edu>; <carter at iram.fr>; <cerni at astro.iem.csic.es>;
<cwalker at zia.aoc.nrao.edu>; <dbock at astron.berkeley.edu>;
<dpw at ovro.caltech.edu>; <efomalon at nrao.edu>; <ewine at strw.leidenuniv.nl>;
<gab at gps.caltech.edu>; <guillote at iram.fr>; <jmangum at tuc.nrao.edu>;
<jsr at mrao.cam.ac.uk>; <lgm at astro.umd.edu>; <lucas at iram.fr>;
<mgurwell at cfa.harvard.edu>; <mholdawa at tuc.nrao.edu>;
<mmaimcal at cv3.cv.nrao.edu>; <mwright at astron.berkeley.edu>;
<plambeck at astron.berkeley.edu>; <pnapier at zia.aoc.nrao.edu>;
<richard at mrao.cam.ac.uk>; <smyers at zia.aoc.nrao.edu>;
<wilson at physics.mcmaster.ca>; "Steve Scott" <scott at ovro.caltech.edu>
Sent: Thursday, August 29, 2002 10:42 AM
Subject: Re: [Almacal] memo 372 review reply - gurwell


> David Woody writes:
>  > The system temperature is inversely proportional to the gain...
>
> This is not true in a system where the gain is stable.  It is true in
> a system that uses automatic level control, in which case the gain is
> deliberately made unstable so as to track variations in the system
> temperature.  I submit that this is a bad idea and should not be done
> for ALMA.  My earlier remarks were based on the plan that ALMA will
> not use ALC and that the gain will be made as stable and predictible
> as possible for each observational setup.  Once it is understood that
> gain is not coupled to system temperature, many of Dave's remarks do
> not apply.
>
> I hope soon to have time to describe more detail the plan that I have
> in mind.  It is, admittedly, somewhat unconventional and it might have
> significant flaws.
>
> --Larry
>