[daip] Re: System temperatures for GB (experiment BP100 on June 26)

[Craig Walker]

We have a cal file for 4cm on the GBT, but it seems to have all Tcals
set to 1.  It clearly needs an update.  We seem to have real numbers
for the other receivers for which there are tcal files, but those 
are not all, especially the higher frequencies.

The calibration values in the AIPS CL table multiply the correlation amplitudes.
Individual antenna gains (and Tsys) affect such gains by the square
root.  So your CLCOR correction should be by sqrt(3).

Craig

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    R. Craig Walker            Array Operations Center
    cwalker at nrao.edu           National Radio Astronomy Observatory
    Phone  505 835 7247        P. O. Box O
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On 2002.08.13 11:18 Jim Ulvestad wrote:
> Dear Miguel et al,
> 
> In AIPS, it is possible to change the values in the CL
> table by using CLCOR with OPCODE='GAIN' to correct
> the Tcal values.  Then CLCORPRM(1) should be set equal to
> either 3.0 or 1/3.0 to convert from Tcal=1.0 to Tcal=3.0.
> The effect should be to increase Tsys, which will increase
> the value that AIPS uses for the complex gain.  Therefore,
> the correct value should be 3.0, but you should look carefully
> (e.g., in a POSSM plot on a fringe finder) to make sure this
> correction goes in the right direction.
> 
> Cheers,
> 
> Jim Ulvestad
> 
> Frank Ghigo wrote:
> > 
> > Dear Miguel,
> > 
> > The BP100.TSYS file has Tsys data for Green Bank that assume
> > the calibration (Tcal) values are 1.0.  Our measurements of
> > RCP Tcal give values ranging from 2.91 at 8.4 GHz to
> > 3.24 at 8.5 GHz.  The Tcal measurements are probably good to
> > about 10%, so it is sufficiently accurate to use Tcal = 3.0 Kelvin
> > 
> > That would mean that you need to multiply all the Tsys values
> > for GB in the table by 3.0 to get Tsys.
> > I don't know how easy this would be to do in AIPS.
> > If necessary, one of the analysts in Socorro should be able
> > to re-generate the Tsys table for you using the correct
> > Tcal values.
> > 
> > The documentation you refer to:
> > > (http://www.aoc.nrao.edu/vlba/html/OBSERVING/cal-transfer/
> > 
> > is dated 1999, and the information about Green Bank actually
> > refers to the old 140-foot telescope.
> > 
> > For the new 100-meter GBT, the Tsys information is supposed to
> > be supplied automatically, similar to how it is done for
> > all the VLBA antennas.  So we should not have to e-mail you
> > the Tsys information any more.
> > 
> > Apparently the calibration transfer was not fully implemented
> > for BP100, but I hope it will be available in future runs.
> > 
> > -- frank
> > 
> > Torres Miguel wrote:
> > >
> > > Dear Frank,
> > >
> > > I'm currently reducing the data for the VLBI experiment BP100 of
> > > last June 26. While reading the information on the calibration transfer
> > > (http://www.aoc.nrao.edu/vlba/html/OBSERVING/cal-transfer/ then click on
> > > "Observations with GB"), I've come across the following sentence:
> > >
> > > "Currently, the TY table contains incorrect data from GB. Correct system
> > > temperatures will be e-mailed to the PI
> > > from Green Bank. The user should then create an ANTAB input file for GB
> > > in the usual, old-fashioned way, and
> > > follow the procedure given in Section 4.1."
> > >
> > > I haven't got any system temperatures from GB. Is it that the new values
> > > are OK (find attached the BP100.TSYS that also includes the TSYS for
> > > GB).
> > >
> > > Thanks in advance,
> > > Miguel
> > > --
>