[mmaimcal]Re: Phase Repeatability of the Attenuators

[Morita, Koh-Ichiro]

Dear Larry and Mark,

Larry D'Addario wrote:
> First, I hope you realize that far more than an attenuator setting
> changes when we switch bands.  The requirement you suggest for the
> electronics applies to the whole system, not just an attenuator.  In
> particular, both of the tunable LOs (1st and 2nd) need to be reset,
> and various switch positions need to be changed.  The LO that's doing
> phase tracking ("fringe rotation"), probably the 1st LO, needs to be
> programmed very differently at each sky frequency.  All of these need
> to be highly repeatable.  We describe this by saying that if the
> observing frequency changes from f1 to f2 and then back to f1, the
> instrumental complex gain should be the same as it would have been had
> we stayed at f1 the whole time.

This is an important comment, I think.
Our LO system for NMA has this problem.  The LO sytem cannot keep
same phase between conditions before and after frequency switch.
So, we have to change between a target source and a reference source 
without any control of the LO system.

I do not know details about ALMA electronics and I want to ask
engineers about this problem.

Regards,
Koh-Ichiro

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Koh-Ichiro Morita
Nobeyama Radio Observatory,
National Astronomical Observatory, Japan
Minamimaki, Minamisaku, Nagano 384-1305, Japan
Email: morita at nro.nao.ac.jp
Phone: 81-267-98-4396
Fax:   81-267-98-4339
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