[daip] Ringing from BPASS

[lincoln greenhill]

Hi Eric,

Ingyin is certainly not yet broadly experienced, and a conceptual
error would not be plausible to anticipate.

I had never seen anyone break bp calibration as she
appeared to have done.  Did she send to you her BPASS
input parameters? I scanned them before she contacted you, and
thought that they looked OK.

She has not gone on to use CPASS, but I will
ask her to return to BPASS as some point so that learning
continues.

Lincoln


Eric Greisen wrote:
> lincoln greenhill wrote:
>> Hi Eric,
>>
>>> I have looked at your data a bit more.  There seems to be a subtle 
>>> difference between the BP table attached to the fits file with only 
>>> 2145+067 (256 chan) and that attached to the fits file containing a 
>>> number of sources.  The BP table attached to the 1-source file causes 
>>> the ringing whether applied by POSSM or SPLIT followed by POSSM on 
>>> the data of the 1-source file or the data of the n-source file.  The 
>>> BP table of the n-source file does not cause ringing when applied to 
>>> either data set which, I suspect, is the cause of your theory that 
>>> SPLIT fixed things.  How the BP table became different is a good 
>>> question.  Forcing the software to ignore the VLBI shifting, the 
>>> "calibrated" data are nearly the same with both BP tables except for 
>>> the outermost couple of channels.
>>
>> If I assume that an FFT is performed to effect the shift in frequency 
>> required
>> for VLBI data, then the problem be triggered by an erroneous value in
>> the highest channel of the transform spectrum (lag domain) - perhaps an
>> array dimension problem?
> 
> No.  It works just fine for everyone else's data and for 1 of the 2 BP 
> tables your student sent on the data he sent.  There is not a software 
> problem but almost certainly a conceptual problem.
> 
> Eric Greisen

-- 
Lincoln J. Greenhill               Harvard-Smithsonian Center for Astrophysics
Office:     1 617-495-7194         60 Garden St, Cambridge, MA 02138
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