6cm band bandpass ripple
Posted: Sat Sep 13, 2014 5:39 pm
Hi guys - quick question. I have reduced some ATCA 6cm data using all of the standard procedures. After MFCAL and GPCAL on 1934, then GPCAL & GPBOOT on the secondary, I ran a quick UVSPEC on the secondary and was slightly alarmed to find a sinusoidal oscillation running through the band in the XX and YY products. I had a poke around on the ATCA forum and found this post on a possibly related issue:
https://atcaforum.atnf.csiro.au/viewtop ... f=11&t=184
Plots 2--4 in that post clearly show a very nasty problem, but then in plot 5 the problem is said to be fixed. However, there still appears to be a sinusoidal ripple. What piques my interest here is that the frequencies of the peaks and troughs in this spectrum match up almost precisely with what I see in my calibrator (relevant plots appended below).
The problem manifests itself on almost all baselines to at least some extent, and the period of the oscillation does not seem to be noticeably dependent on the baseline. I went ahead and imaged the cal every 32 MHz through the band, and while the images look beautiful, the flux density shows the same oscillations when extracted from the images. Copying the calibration solutions to my other sources and imaging them reveals that they then suffer from the effect too.
Have you any idea what causes this? I'm not having a great deal of luck figuring it out or getting rid of it!
Cheers,
Craig.
My cal:
The forum plot:
https://atcaforum.atnf.csiro.au/viewtop ... f=11&t=184
Plots 2--4 in that post clearly show a very nasty problem, but then in plot 5 the problem is said to be fixed. However, there still appears to be a sinusoidal ripple. What piques my interest here is that the frequencies of the peaks and troughs in this spectrum match up almost precisely with what I see in my calibrator (relevant plots appended below).
The problem manifests itself on almost all baselines to at least some extent, and the period of the oscillation does not seem to be noticeably dependent on the baseline. I went ahead and imaged the cal every 32 MHz through the band, and while the images look beautiful, the flux density shows the same oscillations when extracted from the images. Copying the calibration solutions to my other sources and imaging them reveals that they then suffer from the effect too.
Have you any idea what causes this? I'm not having a great deal of luck figuring it out or getting rid of it!
Cheers,
Craig.
My cal:
The forum plot: