327 receiver calibration.


    The 327 Mhz receiver is a dual linear receiver with room temperature amplifiers and a 30 Mhz wide filter.


Sections:

History
Recent system performance measurements
Daily monitoring of tsys.
Calibration measurements
rfi
cal values
rfi measurements
all measurements in date order

haslam et al 408 Mhz all sky survey (.pdf) .. 18.9 Mb

327 rcvr block diagram (.pdf)
327 filter bank (.pdf)

Hybrid between antenna and filters (aug14) (.jpg)


History:

  • 26sep14: hybrid reinstalled.. back to circular.
  • 08aug14: hybrid removed .. alex W. wanted linears.
  • 13jan13: updated pointing offset
  • 06jun11: hybrid installed on antenna.
  • 04jan10: Now cooling is on one of the alfa compressors.
  • 13jun08: Cooled 327 receiver installed. New cal values also installed.
  • 13apr06:  rf cable of channel A between the front end and the filter at the post amp was replaced because it was bad. The cal cable for channel B between the postamp chassis and the antenna was also replaced.
  • 11apr06: 750 Khz comb appeared. 39.45 Khz comb was seen (but not sure when it appeared). Turned out to be the sband cabinet in dome.
  • 07jan04: 327 receiver moved to a new position on the turret floor (to make room for alfa).

  •   jul02: room temperature receiver installed.
    11jul02: cal values measured in lab.


    Calibration measurements:  (top)

    13jan13: calibration results: jun12-dec12. updated pointing offset.
    21jun08: SEFDA/SEFDB shows that tsys polB is 10% larger than tsysB.
    feb05: gain curves  for data taken mar03 to feb05 (GAIN CURVE)
    feb05: system performance for gain curve data mar03-feb05
    08aug02: Calon/off sky and load. Tsys contributions receiver, sky
    07aug02: calibration runs 3C138,B0640+233, and B08224+294


    Rfi  (top)

    feb14: p1693 pulsar search data taken during the cable repair
    10aug11: short duration broadband rfi seen by p2558 in 327 rcvr.
    09aug09: rfi from azimuth encoders
    Cleaning up the 327 Mhz band (last updated 03nov05):

    05nov05: azimuth dependence of birdies in the 327 rcvr.
    21oct05: output of 327Mhz rcvr after the 1st amp (and before the rf filter).
    16oct05: 1 Mhz comb coming from dome AC units.
    27aug05: the 16Khz comb in the 327 rcvr comes from the alfa motor controller.



    All measurements in date order  (top)


    feb14: p1693 pulsar search data taken during the cable repair
    20feb14: total power dropouts seen in p1693 data.
    26jun13: P2717 327 incoherent search with puppi show avg spectra, rms, and rfi.
    13jan13: calibration results: jun12-dec12. updated pointing offset.
    20apr12: bandpass shape of cavity filter in front of dewar.
    10aug11: short duration broadband rfi seen by p2558 in 327 rcvr.
    09mar11: az dependence of 327 rfi
    13dec10: tsys vs ra,dec and l,b 09may09 thru 13dec10
    09feb10: p1693 drift scan 220 sec dynamic spectra  and spectral avgs.
    09aug09: rfi from azimuth encoders
    07may09: tsys vs sky position for jun2008 to may09
    16jul08: tsys vs date,hr,ra,dec with cold receiver
    21jun08: SEFDA/SEFDB shows that tsys polB is 10% larger than tsysB.
    07may07: Strong 60 Hz in p1693 pulsar data using the 327 receiver and the wapps.
    05nov05: azimuth dependence of birdies in the 327 rcvr.
    03nov05: Cleaning up the 327 Mhz band (last updated 03nov05):
    21oct05: output of 327Mhz rcvr after the 1st amp (and before the rf filter).
    16oct05: 1 Mhz comb coming from dome AC units.
    27aug05: the 16Khz comb in the 327 rcvr comes from the alfa motor controller.
    feb05: gain curves  for data taken mar03 to feb05 (GAIN CURVE)
    feb05: system performance for gain curve data mar03-feb05
    08aug02: Calon/off sky and load. Tsys contributions receiver, sky
    07aug02: calibration runs 3C138,B0640+233, and B08224+294
    jul02      :Room temperature receiver installed
    07jan04: 327 receiver moved to new turret position.
    29sep00:Turret posit

    20feb14: p1693 total power dropouts  (top)

        p1693 took data during the main cable 8-4 repair. The data from 20feb14 (after midnite) showed total power dropouts:
    setup:

        The plots show 10 secs of total power data from file 20140220.Strip932.xxx.0000.fits (.ps) (.pdf):

    SUMMARY:

    processing:x101/140220/p1693dat.pro


    20apr12: bandpass shape of cavity filter in front of dewar.

        A noise  source was injected into the cavity filter before the dewar to measure the filter shape. The setup was:
    The plots show the cavity filter shape (.ps)  (.pdf):

    Summary:

    processing: x101/120420/327_filter.pro

    09feb10:p1693 drift scan:

        p1693 did a long drift scan using the wapps on 09feb10. The setup was:
    The first file of data was looked at (about 2 minutes)
    dynamic spectra for 2 minutes of data (.gif):
    plots of the average spectra and the rms/mean (.ps) (.pdf):
    processing: x101/100209/p1693drift.pro

    07may09: Tsys vs ra/dec and Tsys vs galLong/galLat.  (top)

        Tsys data from 13jun08 (start of 327 cooled receiver) thru 07may09 was plotted vs ra,dec and galactic l/b to show the portion of Tsys that is coming from the sky. Only data with zenith angle below 15 degrees was used (to not include the tsys za variation).
    PolA plott

    Tsys vs sky position (.ps) (.pdf):
    Summary:
    Processing: x101/090506/tsysplotradec.pro

    16jul08: tsys vs date,hr,ra,dec with cold receiver  (top)

        The tsys  measurements from 14jun08 to 16jul08 were used to plot tsys vs various parameters to see why tsys was sometimes high.
    The plots show Tsys vs date, hr, ra, dec, za (.ps) (.pdf):  The black * are polA while the red * are polB. Tsys for polB is about 10K higher than polA.
    SUMMARY:

    21jun08: Ratio SEFDA/SEFDB shows Tsys B > TsysA  (top)

        The tsys measurements after the cooled receiver was installed on 13jun08 showed that Tsys PolB is about 10K higher than Tsys polA. To see if this was  a cal problem or a real Tsys difference, calibration scans using the source B0316+162 (CTA21) were done and then the SEFD ratio was computed. The setup and processing was:
    The plots show the calibration measurement results (.ps) (.pdf):

    Conclusion:

    processing: x101/080621/chk327.pro


    28feb05: gain curve for data taken mar03 to feb05  (top)

        Calibration data taken march03 to feb05 was used to fit a gain curve for  the 327 receiver (the data was taken at 326 Mhz). For the data to be included in the fit, it had to satisfy the following constraints: These constraints were used to remove some bad measurements. The cal values used were those measured in the lab in jul02 (see the system performance for gain curve data for a more complete description).
        Gain curves were then computed fitting for gain as a function of za. The fitting function (with za in degrees) is:

         g(za)=c0 +c1*za + c2*(za-14)^2 +c3*(za-14)^3

    where the ^2 and ^3 terms are only applied for za ge 14 degrees.
         The plots show the gain curve and the residuals (.ps)    (.pdf):

    The source with low flux (red x ) i s B0320+053. Its flux may be a bit off. At 1400 Mhz our flux differs from nvss by about 8%. The yellow diamonds that are high come from B0521+281. The cal values for the 327 receiver have jumped around by up to 10  kelvins in the last two years (see 327 Mhz tsys difference  2004,2003).  If the polA-polB jump was do to a shift in the cal, then it will affect any calibration data taken during these jumps (i guess i need to check this out..)
        The fit coef can be found in the ao idl distribution in the file data/gain.datR1. At AO it is found in the file /share/rsi/local/libao/phil/data/gain.datR1.
    processsing:  x101/327/feb05/dogaintfit.pro


    28feb05: system performance for gain curve data mar03-feb05 (top)

        Calibration data taken mar03 to feb05 was used to fit gain curves for the 327 receiver. For the data to be included in the fit, it had to satisfy the following constraints: These constraints were used to remove some bad measurements. The cal values used were those measured in the lab in jul02. The plots show the system performance for the gain curve data (.ps) (.pdf)  : processing: x101/327/feb05/doit.pro


    07jan04: 327 receiver moved to new turret position.   (top)

        The 327 receiver was moved on 07jan04 from turret position 21.5 to turret position 340. This was done to make room for the alfa receiver. Calibration scan data was taken on 05,06jan04 before the move and on 07jan04 after the move. The goal is to make the average pointing error  before and after the moves the same. The az error can be manipulated by changing the turret position, the za error can only be modified by moving the feed.
        The pointing error before and after the move is shown in the plots. The za pointing error remained within 1 arc second. The azimuth pointing error for source 2 on the second day (green) varied with za (tiedown losing tension??). To compute the mean (actually median values) I only used source 1.
     

    medianAzErr
    asecs
    medianZaErr
    asecs
    before move(tur=21.5) -11.73 -17.05
    after move (tur=340.2) -26.84 -16.39

    The average az error with the turret at 340.2 degrees is (-11.73-(-26.84))=15.1 asecs too small. We need to move the azimuth by +15.1 asecs. The turret coordinate system is opposite to the azimuth and 1 turret degree equals 45 arc seconds on the sky. The turret needs to be moved to 340.2-(15.1/45)=339.9 This will be the new turret position.


    08aug02:calOn/off load and sky. Tsys contributions receiver, sky.  (top)

        30 cal on offs were done while the load switch was on , and 30 more calon/offs were done while tracking blank sky (ra:075055, dec:240000). The telescope was centered at 327 Mhz and 25,12.5,6.25, and 3.125 bands were used. 2 seconds cal on were followed by 2 seconds cal off. The cal values used were: 73.2 pola, 76.1 polB.
        The load is beneath the rotary floor close to the antenna. The temperatures were: room:92, platform:85, tertiary platform:92 (this was after an sband radar run). Remeasuring these values 20 minutes later, the temperatures were all within 1 F of the original values. Using an ambient temperature of 90F gives a load temperature of 305K.
        The plots show the system temperature measured for the cal on/offs. The lines are calOff, the * are cal on. PolA is black while polB is red.

        On load calOff the average temp was 375K. Using 305K for the ambient load temperature gives a noise contribution from after the load of 375K-305K=70K for a noise contribution after the load switch. This is what is expected for the room temperature amplifier.
        On sky calOff the average temp was 135K. This includes the flange temperature, sky temperature, and any ground/scattered/spillover radiation. Using 40K for the sky contribution and 70K for the flange temperature gives 25K from the spillover/scattered ground radiation. Higher frequency receivers have shown scattered radiation ranging from 10 to 20 K so 25K for the 327 receiver seems reasonable.
         The sky temp was crosschecked with chris salters 408 Mhz survey and it came out to 39.1K.
     
    327 Tsys budget
    load temp 305K
    receiver temp 70K
    Tsys on sky 135K
    sky temp 40K
    spillover,scattered radiation 25K

     processing: x101/020808/docal.pro


    07aug02: calibration runs 3C138,B0640+233, and B0824+294  (top)

        Calibration runs using the heiles scan were done on 3C138 (B0518+165), B0640+233, and B0824+294 during the day. The first two sources were done after transit, while the last (B0825+294) covered 2 strips before transit until set. B0640+233  has a width of 72" by 17" at lband while the other two sources are < 16".  The field has other sources within the +/-3 beams that were on the order of 3% of the source. The plots show the calibration results:
  • Fig 1. has gain Kelvins/Jy, Tsys, Sefd, and average beam width. The za dependence of the gain and tsys look correct. The gain is about 11 K/Jy, Tsys about 150 K, SEFD 14, average beam width: 14 Amin
  • Fig 2 shows the coma parameter, first sidelobe height: -14 db, main beam efficiency 65% (using 3C138), and main beam + first sidelobe efficiency of 80% (using 3C138)
  • Fig 3 has the pointing errors for these runs. Most of the data was taken after transit so the pointing errors may be biased to one part of the dish.  The mean za Error is -142 Asecs with an rms of 34 Asecs. The feed is pointing too far downhill. The mean azimuth error is -3 Asecs with an rms of 24 Asecs. This feed was not surveyed into position. The mean pointing error can be fixed by updating the model for 327. (Note: updated pointing model 07aug02).

  •  
    measured 327 performance
    gain 11 K/Jy
    Tsys 150 K
    sefd 14 Jy/Tsys
    avgBeamWidth 14 Amin
    First sidelobe -14 db below peak
    mainBeamEffciency 65%
    processing: x101/020807/doit.pro


    jul02   Room temperature  receiver installed

        The 327 receiver had been removed in 2001 to be worked on. It was re-installed in jul02 with a room temperature receiver.


    29sep00: Turret Position:

    The 327 system was installed in late september under the turret floor. For a number of receivers we have found a local maximum in the system temperature when the turret is aligned with the optic axis. I did a number of turret scans on blank sky to find the turret position of this local maxima.
    setup:
    On 29sep00 the turret was driven in a sine wave about turret=22 degrees with an 8 degree amplitude and 15 second period. The telescope was parked at az=270, za=10. 2 polarizations were recorded. Each was detected with a .02 sec time constant.
    The turret strips figure shows the average of 8 minutes of data tsys versus turret position. The top plot is polA and the bottom plot is polB. The units are a/d counts with the average value as the system temperature.  The local maxima occurs at 24.5 deg (polA) and 17.5 deg (polB). The turret scale factor  is 45 arcsecs (great circle) per turret degree. If the difference is caused by a misalignment of the dipoles then it is about 5.25 arcminutes or 1/3 of a beam. We need to do some scans on a continuum source to verify that this is beam squint.
    processing: x101/000929/chkpnt.pro
    home_~phil