Dome 430 MHz calibration

Sep 2004

     There is a 430 MHz receiver on the gregorian dome. It can be used for transmitting and receiving. It has native circular polarization.

Sections:

History
Recent system performance measurements
Daily monitoring of Tsys
Dewar temperatures
Calibration measurements
Measurements in date order
Cal values
rfi measurements

History:

30jun11: radioastronomy,radar switch polA was bad. removed 27jun11 and repaired it. Probably causing the ripples in polA band pass
19jul06: tsys polB increased. Stayed high till about 10aug06. The jennings relay for polB was bad.
18jul06: new turnstile installed. Better isolation. Still needs to be tuned a bit.
25may06: power supply for cal driver circuitry was bad. replaced it.
23may06: tsys starting to go infinite.. turns out power supply for cal driver went bad.
27jan05: filters (both pols) installed before dewar to get rid of tv station intermods.
oct04: filter placed in front of dome polA dewar removes tv station intermods.

Calibration measurements:

mar03  -  oct03: GAIN CURVE.

Measurements in date order:


28jul11,23jun11,17may11: 430 dome polA bandpass irregularities (top)

Note:

    The 430 dome polA bandpass has shown variations in its bandpass. They  first appeared on 30mar11. The x111 rfi monitoring data was used to check when it occurred. The x111 data processing was:
The plots show the 430 dome x111 rfi monitoring data for mar thru 22jun 2011 (.ps) (.pdf):
Summary:
processing: x101/110428/430polAripple.pro

27sep10: check 430 stability  (top)

    PolA 430gr was unstable back on 10aug09. On 27sep10 data was taken to see if the problem still persisted. The setup was:

data images, plots:

Summary:

processing: x101/100927/chk430.pro

10aug09: 430 polA unstable (top)

    Project a2415 reported that 430 dome polA was unstable with a 15 second periodicity. Data was taken on 10aug09 AM with the mock spectrometers. The setup was:
    The total power for the 300 seconds of data was computed for each .1 second sample after throwing out rfi (compute rms/mean by channel and throw out channels with large rms). The total power was then normalized to the median value over the 300 seconds
    The plots show the total power and spectrum of the total power (.ps) (.pdf) :

Summary:

processing: x101/090810/430.pro

mar03 thru oct03 GAIN CURVE. (top)

    Calibration data taken mar03 thru oct03 was used to compute a gain curves. The fits were done versus za. The plot shows the data, fits, and the residuals. This needs to be redone once the filters are installed on the frontend  (to cut out the tv stations).

11jan05:  TsysPolA - TsysPolB drift for 2003 and 2004 (top)

   The system temperature for the dome 430 receiver is measured regularly during the normal maintenance
procedure. I've plotted Tsys for the years 2003 and 2004 (.ps).  (.pdf)

     Fig1-  Top: Tsys for 2003. Black is polA, red is polB, Bottom: TsyspolA-tsysPolB
     Fig2:- Top: Tsys for 2004. Bottom: TsysPolA-TsysPolB

    From the plots you can see that the difference TsysPolA-TsysPolb has been changing. In july 2003 the difference started to increase (TsysA larger then TsysB). Around 17nov03 the difference jumped by 10 degK so that TsysB was larger then tsysA by about 10 degK.   It stayed at this level until august 2004 when it started to increase gradually.
      The tsys measurements tend to be taken at 16:30 AST so the RA of the measurement will move during the year. It seems unlikely that the gradual drift  in TsysPolA - TsysPolB is coming from the sky since the receiver is circularly polarized (and there are no extended sources of circular polarization that i know of).   Looking at the src deflections over this time period the polA,polB ratio remained fairly constant, so my guess is that Tsys was changing (and not the cal size).

    processing: x101/430/tsysByYr.pro
  

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