sbn Tsys 2017. Shutter problems



    The sbn system temperature checks have occasionally shown a tsys much lower than the expected values.  This was occurring in both polarizations.

    The plots show tsys (using hcorcal) vs date for jan17 to may17 (.ps) (.pdf)

    To get a lower tsys, the value of the cal must increase, or the system temperature most really be lower.
    When the sband shutter is closed, the system temperature measures the reflected power from the cooled lna's. This is lower than the Tsys measured on sky.

    On 08may17 felix and I took system temperature measurements with the shutter open and closed. When open we got around 25 K. When the shutter was closed we got about 12K.

    We then found that:

This would explain why we had occasional  measurements of 12 degs for sbn Tsys:


processing: x101/170508/