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:

13sep13: ripple in polA (it's been there awhile). Tapping on polA again caused jumps.
09sep13: polA cavity filter repaired (loose solder joint) and then reinstalled. both jennings relays now look ok.
05sep13: polA cavity filter (before amp) was removed. Its loss was changing by up to 5db when tapped. This was probably causing the polA Tsys jumps.
05sep13: polA jennings relay switched with polB jennings relay (during radar run).
27aug13: polA jennings relay found to have large resistance. Replaced with spare Jennings relay. Tsys back down to around 60K
27aug13: damaged "new" turnstile replaced by "old" 2006 turnstile. Tsys polA back to 60K.
05aug13: waveguide assembly damaged during ao19 removal. floor rotated, and hook on hoist caught turnstile on the adjustable backshort
04apr13: Today found that polB jennings relay had been installed reversed. It was switching sky between load and lna, not lna between sky and load. reinstalled correctly.
??mar13: jennings relay polB reinstalled. Back from repair.
14jan13: polA cable dewar to if/lo rack had problem .. it was replaced.
21jan13: polB amp failed (450-12) . probably the ch xmter since no jennings relay on polB. replaced with repaired amp (450-18) 25jan13.
13jan13: updated pointing offsets.
03dev12: put spare cavity filter from chPolA in front of dome polA to see if ripples went away (no).
30nov12: polA cavity filter removed to see if it caused the ripples (no).Also check for digital tv intermods without filter (yes)
18oct12: jennings relay polB bad. removed. 19oct12 reinstalled for some tests and then removed again.
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:


Measurements in date order:



05feb14 ratio of backscatter gain to on axis gain.

    Herb  carlson and frank djuth wanted the backscatter gain for the 430 dome.
15 heiles calibration patterns on B0316+162 (CTA21.. point source with a flux of 8.7 Jy) were used. Carl's patterns consist of:

Computing the back scatter gain:

For each pattern (15*4=60) , a 200x200 pixel beam map (bmap) was created by evaluating  the fit values that pattern
The first  image shows an example of a single beam map (.gif)
Each map was normalized to unity (the on axis gain = 1).
the ratio of  (integral(bmap^2)/integral(bmap) was then computed. Multiplying this ratio by the on axis gain should give the back scatter gain.
The plots show the results of the computation (.ps) (.pdf)
processing: x101/140204/430grbmmap_herb.pro



13sep13: polA ripple aug13-sep13   (top)

    On 13sep13 we tested polA of 430 dome because the tsys had started to jump around again. The test was:

    spectral line data was also taken while tapping.
    x111 data from 01aug13 -> 13sep13 was then used to see how the bandpass rippled changed with different configurations of the system.
    The plots show the bandpass shapes (.ps) (.pdf):

Summary:

processing: x101/130913/430test.pro


05sep13: polA cavity filter removed. polA jennings replaced.  (top)

    On 05sep13 around 10:00 the aeronomy experiment was stopped to switch the radar  room temp miteq amp with a cooled version.


05aug13: turnstile damaged (top)

    The turnstile (install 2006) was damaged on 05aug13 while removing ao19. The winch was left hanging and hooked the adjustable backshort on the edge of the  turnstile when the rotary floor was moved. This bent the turnstile.

Tsys polA remained 200-300 K till 16aug13..

The damaged turnstile was replaced by the pre 2006 turnstile on 27aug13.

03apr13: polA Tsys jumps high in afternoon.  (top)

04apr13: resolution: polB jennings relay had been installed backwards. It was switching sky between load and lna instead of lna between load and sky. reinstalled correctly.  This means that the high polA Tsys was probably both were on load.

    Since around the 31mar13 some afternoon tsys measurements have shown TsysPolA to be much higher than polB (250 to 400 K vs 100)
Plots were made of the hcorcal tsys for 430 using data 21mar13 through 03apr13(am).
The plots show tsys vs date, hour, and lst (.ps) (.pdf):

Comments:

processing: x101/1304030/tsys430.pro




02dec12: sweep notched filter in front of dewar. (top)

    A single pole cavity filter (with notches for the analog tv stations) was placed in front of the dewar 27jan05. The polA filter had problems with the input connector (a c-clamp was added to replace one of the 4 screws holding the connector). This filter was replaced by one of the single pole cavity filters from the carriage house (around 02dec12)  The filter with the connector problem was swept by dana (down in the lab).
     The plots show the filter response (.ps) (.pdf):
processing: x101/121202/430filterswp.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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