CABB Zoom Mode System Temperatures (20cm)

[JamesAllison]

Hi All,

I'm making my way through 3 days worth of CABB 20cm data and have noticed an issue with the recorded system temperatures in zoom mode data at 1.3GHz. Looking at the amplitude of 1934-638 (e.g. Baseline 1-2, with basic flagging and zero calibration) we see ~30% variation over 12hr periods, and the corresponding recorded system temperature is constant (e.g. Antenna 1):



In contrast the simultaneous 2GHz "continuum" band data apparently do have correctly recorded system temperatures, which is seen in the example 1934-638 data:



I would be grateful for any advice or comments, I expect a possible solution is to use the system temperature information from the 2GHz band to correct the data in the 1.3GHz zoom band.

Cheers,

James

[ste616]

Hi James,

The noise diode that we rapidly switch on and off to determine the system temperature in real time is not considered by the zoom bands, thus the system temperature for those bands will remain constant (as you have discovered). You will need to use the system temperature information from the 2 GHz band, which itself may be faulty since it is only coming from the "tvchannels", which don't usually include all the RFI present at around 2 GHz. There are some Miriad tasks to help recalculate the system temperatures during data reduction, but I'm not sure of their usability at the moment. Perhaps Mark Wieringa can answer your question about that.

[JamesAllison]

Hi Jamie,

Thanks for your reply - I'll contact Mark and see if he has any suggestions.

Cheers!

[JamesAllison]

Hi All,

Just a brief follow up on this issue.

I have constructed a small task for Miriad which removes the existing Tsys weightings from all the
correlation data, and then re-applies only the IF1 Tsys weightings. This will likely only work if the
Tsys values in IF1 are applicable to the other observed frequency windows.

Drop me an email if you would like the fortran source code.

Cheers,

James

[Mark.Wieringa]

Hi James,

Sounds like you're fast becoming a Miriad expert.
If you send me the code I'll see if I can get it into Miriad for general use.

Cheers,

Mark

[JamesAllison]

Hi Mark,

Sure - I've sent it to you in an email. I made a slight modification so that the user can
specify which of the IFs the Tsys measurements are taken from.

Cheers,

James

[Mark.Wieringa]

Hi James,

I've incorporated your code into the attsys program, as option 'redo'.
It should appear in the miriad distribution by tomorrow.
Meanwhile Bob Sault has been looking into fixing the issue in the CABB software and producing a sensible tsys for the zooms in future.

Cheers,

Mark

[JamesAllison]

Hi Mark,

That's great,

Cheers,

James