[daip] [Fwd: ACCOR output]

[Craig Walker]

I looked at the actual power levels in the BBCs for that run and they 
were low, and variable, in channels 5 and 7 (higher frequencies LCP). 
These are the power levels after the autoleveling and should be nearly 
constant.  I'm not sure of the reason, but presumably the power coming 
down from the antenna was lower than it should have been.  With low 
autoleveled powers, the clipper levels will not be at the right fraction 
of total power and you will see exactly what your plot shows.  Hopefully 
the ACCOR corrections will do what is needed to fix things up.  There 
will be a small loss of SNR, but I don't think it should be very bad. 
But you might want to avoid using those channels as part of your 
absolute amplitude calibration (ANTUSE in CALIB).

I checked a later run of your project and don't see any sign of the 
problem.  I presume whatever the trouble was, it got fixed.  The system 
does let the operators know about low power, but it is likely to take 
site tech intervention to fix it and that would generally not be done 
during a run.

Cheers,

Craig




Ingyin Zaw wrote:
> The expt was in Jan. 2008. Thanks,
> Ingyin
> 
> On Tue, 21 Apr 2009, lincoln greenhill wrote:
> 
>> Dear Leonid, Craig,
>>
>>
>> Attached is a plot showing output from ACCOR (3 VLBA stations, 8 IFs 
>> overplotted) for a 22 GHz phase referencing expt in Nov. 2004.
>>
>> We used solint = -0.25 .
>>
>> I have not previously see the signature shown here for OV, where 2 of 
>> 8 IFs
>> show a rapid and systematic variation in sampler statistics.  Is the
>> behavior familiar?  Do you know what could cause it?
>>
>> Best, L.

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     R. Craig Walker            Array Operations Center
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