Oscillations in 1934 spectrum after bandpass cal
Posted: Fri Jan 18, 2013 4:09 pm
Hi guys,
So I'm trying to get a good bandpass cal for some 16cm CABB data, but when I use UVSPEC to look at the spectrum of 1934 afterwards, I'm seeing oscillations in Stokes I at the lower end of the frequency band, typically on all baselines except for those including ant 6. This doesn't seem right to me, but I have been pretty fastidious about iteratively deriving bandpass solutions and flagging, so I was hoping you might be able to tell me if something is wrong, or if this is as good as it gets.
My calibration does the following:
#initial MFCAL
mfcal vis=1934-638.2100 refant=4 interval=5
#initial flagging
pgflag vis=1934-638.2100 stokes=xx,yy device=/xs command=<b
pgflag vis=1934-638.2100 stokes=yy,xx device=/xs command=<b
#BLFLAGing / manual flagging in here
#MFCAL
mfcal vis=1934-638.2100 refant=4 interval=5
#another round of flagging
pgflag vis=1934-638.2100 stokes=xx,yy device=/xs command=<b
pgflag vis=1934-638.2100 stokes=yy,xx device=/xs command=<b
#BLFLAGing / manual flagging in here
#final MFCAL
mfcal vis=1934-638.2100 refant=4 interval=5
#GPCAL
gpcal vis= 1934-638.2100 refant=4 interval=20 nfbin=16 options=xyvary
I then use UVSPEC to take a look at the results:
Task: uvspec
vis = ./1934-638.2100
select =
line =
stokes = i
interval = 10
hann =
offset =
options =
axis = freq,amp
yrange =
device = /cps
nxy =
log =
With options=nobase,avall set, the spectrum looks really smooth as you would expect. However, with options unset so I can look at individual baselines, I typically get plots that look like the following:
I've tried many combinations of MFCAL settings, GPCAL settings, light flagging, heavy flagging, iteratively flagging then solving for bandpass and back again etc. Each time, I get the same result more or less. So my questions are:
1) Is there anything wrong with what I'm seeing here in UVSPEC?
2) If so, is it likely to be RFI, a lack of unflagged data to derive solutions from, or some other problem with how I've run things?
And hints, tips or help would be much appreciated!
Cheers,
Craig.
So I'm trying to get a good bandpass cal for some 16cm CABB data, but when I use UVSPEC to look at the spectrum of 1934 afterwards, I'm seeing oscillations in Stokes I at the lower end of the frequency band, typically on all baselines except for those including ant 6. This doesn't seem right to me, but I have been pretty fastidious about iteratively deriving bandpass solutions and flagging, so I was hoping you might be able to tell me if something is wrong, or if this is as good as it gets.
My calibration does the following:
#initial MFCAL
mfcal vis=1934-638.2100 refant=4 interval=5
#initial flagging
pgflag vis=1934-638.2100 stokes=xx,yy device=/xs command=<b
pgflag vis=1934-638.2100 stokes=yy,xx device=/xs command=<b
#BLFLAGing / manual flagging in here
#MFCAL
mfcal vis=1934-638.2100 refant=4 interval=5
#another round of flagging
pgflag vis=1934-638.2100 stokes=xx,yy device=/xs command=<b
pgflag vis=1934-638.2100 stokes=yy,xx device=/xs command=<b
#BLFLAGing / manual flagging in here
#final MFCAL
mfcal vis=1934-638.2100 refant=4 interval=5
#GPCAL
gpcal vis= 1934-638.2100 refant=4 interval=20 nfbin=16 options=xyvary
I then use UVSPEC to take a look at the results:
Task: uvspec
vis = ./1934-638.2100
select =
line =
stokes = i
interval = 10
hann =
offset =
options =
axis = freq,amp
yrange =
device = /cps
nxy =
log =
With options=nobase,avall set, the spectrum looks really smooth as you would expect. However, with options unset so I can look at individual baselines, I typically get plots that look like the following:
I've tried many combinations of MFCAL settings, GPCAL settings, light flagging, heavy flagging, iteratively flagging then solving for bandpass and back again etc. Each time, I get the same result more or less. So my questions are:
1) Is there anything wrong with what I'm seeing here in UVSPEC?
2) If so, is it likely to be RFI, a lack of unflagged data to derive solutions from, or some other problem with how I've run things?
And hints, tips or help would be much appreciated!
Cheers,
Craig.