[evlatests] P-Band

[Jim Jackson]

Since this is essentially a parasitic oscillation, it is hard to pin 
it down to a more specific frequency - it could easily move around. 
The frequencies you mention are sufficiently close that it will 
likely cause problems with the IF A/C T304 ALC and/or overload 
problems in the FIR filters in the deformatters.  Depending on the 
bandwidth you use, it may or may not affect the T5 ALC.  We are 
working on a couple of interim solutions to the problem - either is 
sufficiently simple to implement so that Oct 31 date shouldn't be a 
problem. Of course the long term solution is redesign/update the 
P-band receivers.

Jim

At 10:06 AM 10/11/2007, Craig Walker wrote:
>Do you have a more accurate frequency than "6.7 GHz"?  It is likely to
>be outside the band of interest in which I imagine it can be ignored,
>but I wanted to raise this flag just in case.
>
>Cheers,
>
>Craig
>
>
>Charles Kutz wrote:
> > For the interim we can power down the EVLA P-Bands for that observation
> > if we do not have the "fix" in at that time.
> >
> > Chuck
> >
> > Craig Walker wrote:
> >> There is going to be a VLBI observation of the methanol maser on
> >> October 31 (GB063A) using Y1.  The exact frequency of the maser is
> >> 6668.5192 MHz.  The observation will also observe continuum sources
> >> using the frequency range 6621-6699 MHz.  Is the "6.7" GHz signal in
> >> those bands?
> >>
> >> Craig
> >>
> >>
> >>
> >> Claire Chandler wrote:
> >>> They may not affect overall power levels but 6.7 GHz coincides with
> >>> the methanol maser frequency and we may have upcoming observations at
> >>> this frequency that would be affected.
> >>>
> >>> Claire
> >>>
> >>> On Thu, 11 Oct 2007, Charles Kutz wrote:
> >>>
> >>>> The P-Band receivers in antenna 11 and 21 have been turned back on.
> >>>> These units generate strong C-Band RFI at ~ 6.7GHz in antenna 11 and,
> >>>> ~6.7GHZ and ~6.9GHz in antenna 21. We are working on the root cause and
> >>>> the solution.
> >>>> We are in the process of documenting other observed occurrences in
> >>>> other
> >>>> EVLA antennas. These signals are there and may be a nuisance only.
> >>>> These
> >>>> "birdies" should not have a large impact on observations since they are
> >>>> low enough in power that they do not affect leveling in the T304 and
> >>>> are
> >>>> CW signals that appear to be very stable in frequency.
> >>>>
> >>>> We are working on it.
> >>>>
> >>>> Chuck
> >>>>
> >>>> _______________________________________________
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> >>>> http://listmgr.cv.nrao.edu/mailman/listinfo/evlatests
> >>>>
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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
>      Fax    505 835 7027        Socorro NM 87801   USA
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