Xband receiver


     The xband receiver (7.8 to 10.2) Ghz was installed on 19dec01 in the gregorian dome. It is a native circular receiver with setup as: horn, omt, dewar (isolator, calcoupler,amplifier), then postAmps. It is inserted into port 11 of the upstairs if/lo. The IF processing uses the 2 to 12 Ghz mixer to mix down to the  1 to 2 Ghz 1stIF (prior to 3aug03 the receiver used the 10 Ghz upconverter for the 1st IF mixing). This gives an instantaneous bandwidth of 1 Ghz. When using the 2 to 12 Ghz mixer it is
important to use a low side lo below say 8500 Mhz.
04nov16: polA (rcp) (left hand rack downstairs), polB (lcp) (right hand racks downstairs).  .. measured using jpl xband transmitter.

Sections  (top)

Recent system performance measurements
Daily monitoring of Tsys
Dewar temperatures
Calibration measurements
Miscellaneous measurements
Cal values
Rfi measurements

Installation (prior to 15feb02)

History  (top)

Calibration measurements  (top)

16aug12: installed new cal values that were measred ju12. (backdated to 01may12).
12jan06: check xband receiver after reinstallation.
13jun04: xband performance above 10 Ghz.

18mar04: Tsys vs frequency.
25jan04: xband gain curve using  data 05oct03 thru 25jan04.(GAIN CURVE)
05sep03: New horn performance: SEFD new horn,old horn.
05sep03: Compare (SEFDB/SEFDA) and (TsysB/TSYSA)
05sep03: Tsys vs frequency old and new horns.
03jun03: polb gain variations a1704 recomb lines
mar03: xband gain curves mar03 thru sept03  (GAIN CURVE)
21feb02:calibration runs on B0518+165(3C138),B1040+123,and B1328+307(3C286)
21feb02:beammaps (turret scans) J0237+288 after pointing offsets.

Miscellaneous  (top)

09apr14: xmit at 8351 Mhz tone from the control room
05jul13: polA jumps went away when bias box from cbh was used.
01jul13: instabilities seen in pola and polb
16aug12: installed new cal values that were measred ju12. (backdated to 01may12).
16may08: on/off position switching integrating up to 140 minutes. Showing bandpass and total power stability.
11mar04: new cal diodes.
08jan04: xb rcvr moved to new position on turret floor.
17sep03: Resonances in the xband receiver.
21jul03: update az,za pointing offsets using calibration data.
26jul02: xband gain is modulated at 1.2 hz by the crosshead.
jul02: Integrating multiple drift scans. Tsys vs Time, DTsys/Tsys after integration.
06mar02:HC3N,HC7N in TMC1.
21feb02:HC3N lines at 9097,9098,9100 possible detection??

Installation:   (top)

    - update az,za offset model 13. az:+J0237+28827.4, za:+5.4 (from 13feb02 data).
13feb02: beammaps (turret scans) J2253+161,3C48
13feb02: pointing error, squint, tsys, and sefd for J2253+161,3C48.
02jan02: calibration run o     n J2253+161, J0137+331 (3C48)
27dec01: beammaps (turret scans) of J2253+161.
27dec01: pointing error beam widths from turret scans.
20dec01: First (out of focus) light.
20dec01: The cal values and Tsys versus frequency.
20dec01: Power levels in the upstairs if/lo.
19dec01: Rfi seen using the xband feed.
19dec01: Measuring the turret position of the feed.

09apr14: xmit tone from the control room.

    On 09apr14 we transmitted a tone from the control room towards the telescope. The setup was:
    This will verify that the upstairs lo's are locked to the station clock. It also shows the phase noise in the sampled signal.

The plot shows the spectrum of the recorded time domain samples (.ps) (.pdf):


processing: x101/140409/xbtone.pro

12jan06: check xband receiver after reinstallation.  (top)

    The xband receiver was brought down to the lab for some work in jan06. It was reinstalled on 11jan06. On 12jan06 and 13jan06 calibration scans were done on the source B1345+125 (2.17Jy at 9Ghz) to check the receiver. The same source was tracked on both days to see if the values were repeatable. On 12jan06 there were a few clouds. On 13jan06 it was clear. Data was taken 7am to 8am (ast).
    The plots show the results of the xband calibration measurements (.ps)  (.pdf):     The data shows that there is no  large pointing error caused by the re installation. The data from the two days are repeatable which says that things are stable (the Tsys difference may be from the weather). The gain variation with za as well as the sidelobe variation is probably a focus/collimation problem.
processing: x101/060112/chkxb.pro

13jun04: xband performance above 10 Ghz.   (top...)

    The performance of the xband receiver above 10 Ghz was tested on 12jun04 and 13jun04.  Calibration scans were done with  the source B1040+123 (.91 Jy at 11 Ghz) on 12 and 13 jun04. The source B1328+307 (3C286, 4.4 Jy at 11 Ghz) was used on 13jun04. The bandpass filter was removed from the receiver for this test. The 2 to 12 Ghz mixer was used with a high side lo.  Since no filter was present,  some of the other side band would be mixed in. The cal values used were measured on the hilltop test range. The plots show the system performance (ps)  (pdf). The different frequencies are color coded: black-10.5Ghz, red-10.7Ghz, Green=10.9Ghz, blue-11.1 Ghz. The sources are plotted with different symbols.     The sefd is around 14  up to a za of 16 where it starts to rise.  This compares with an sefd of about 9 at 9200 Mhz. The setting track of B1328+307 has a large increase of gain, sefd, beam width, and coma for this part of the dish/rails. This increase is also seen at lower frequencies.

08jan04: xb rcvr moved to new position on turret floor.  (top...)

    The xband receiver was moved on 08jan04 to make room for the alfa receiver. Data was taken on 05-07 jan04 before the move with the turret at 161.4 degrees. On 08jan04 the receiver was moved. Data was taken on 21-22jan04 with on the same sources with the turret at 310.22.  The average pointing error in azimuth for the before and after runs were computed. The difference was made zero  by moving the turret from 310.22 to 309.94. The plots show the pointing errors for the 3 measurements.
  1. Fig 1: this is the azimuth za coverage for the 3 measurements. Black is before, red has tur=310.22, and green is with turret at 309.94 .
  2. Fig 2: The pointing error for the 3 measurements. The median pointing errors were:


    pos1: before
    pos2: tur=310.22
    pos3: tur=309.94
These are the mean (actually median) pointing errors (not the rms error).  These pointing errors are to be subtracted from the computed position to have the telescope point on the source.  The turret was moved from 310.22 to 309.04 so that the mean pointing error for these sources was the same as before the move. There was not adjust possible in the za direction. To go from tur=310.22 to 309.94 using the above data:
  1. Let Pos S have the  telescope pointing directly at the source.
  2. Pos 1 is 1.42 asec greater than Pos S in az.
  3. Pos 2 is 11.64 asecs less than Pos S in az.
  4. To go from pos 2 to pos 1, you must move the azimuth 13 arc seconds (positive).
  5. The turret coordinate system is counter clockwise with 45 asec/turretDeg. + 13asecs of azimuth is -13./45=.28. The new turret position is then: 310.22-.28=309.94.
    The az error is within .5 asecs, the za error is off by 4 asecs from what is was before. These numbers are approximate since the final run at pos3 did not cover the same az/za range az pos1,2. It's probably good enough until we get a chance to survey the horn in position (sometime in feb04).

17sep03: Resonances in the xband receiver. (top...)

    On off position switching was done on 3C454.3 with the xband receiver to check for resonances in the receiver. 8000 to 10000 Ghz was covered. The OMT of the xband is cooled to about 20 K. If a resonance occurs in the omt, then a fraction of the  input sky+source temp will be replaced by the 20K of the omt. For off source measurements, 20K is close to the temperature of the 3K background plus the scattered radiation so there will not be a noticeable bump in the off position. The on source position (probably about 12Jy or 40 Kelvins) will be replaced by a lower temp so there should be a dip at the resonance.
    The plots show on/off - median(on/off) with the resonances flagged in green. Black is polA and red is polB. The units are Tsys. The discontinuities every 20 Mhz are from the different 25 Mhz bandpasses (with had an overlap of 2.5 mhz).

05sep03: new horn performance. SEFD old and new horn.  (top...)

    The xband receiver had a new horn installed on 04sep03. The  x102 calibration data taken before and after the horn change were used to compare the horns. The SEFD before and after the horn change show  how much  system performance improved. The improvement will come from a gain increase and a decrease in Tsys (since Sefd is Jy/Tsys). Most of the Old horn data was taken around april,may 2003. The new horn data was taken in sep03.         The SEFD (Jy/Tsys) improved 25 to 30 % with the larger increase at the lower frequencies. At 9 Ghz the sefd is close to 8 Jy/Tsys. People should be warned that this data was taken in the calibration mode which searches for the peak. The 8 Jy/Tsys does not include any pointing errors that normal observations would encounter.
processing: x102/030905/hornsefd.pro

05sep03: Compare (SEFDB/SEFDA) and (TsysB/TSYSA) using x102 calibration data (top...)

    The system temperature for polA and polB is different.  (see below). This could be caused by a real difference in the system temperatures or it could be an error in the cal values used to compute the system temperature.  To check this you can use the power from a continuum source rather than the cals to measure the values for Tsys. This assumes that the telescope  gain for the two polarization's are the same and that the sources are not polarized. Since  xband is circular polarization,  source polarization is probably not a problem.

    The x102 calibration data for sept 09,10,11  was used for this test. I  re analyzed the data since the normal processing combines the two polarization's and computes Tsys for stokes I. I refit the data using a 2d gaussian fitting for : Amp, offsets, major axis, coma, and coma angle. I did not try to fit for the sidelobes so the data is probably not as accurate as the default processing. The SEFD is Tsys in Janskies. It only relies on the source flux to be correct (the ratio sefdB/sefdA only depends on Tsys). You can compare the ratio of TsysB/TsysA using kelvins from the cal or Janskies from the source.

    The plots show the SEFD and Tsys for the 3 days of xband data.

The tsys ratio using the cals does not match the Tsys ratio using the source for frequencies 8500,8800,9000, and 9200 Mhz. It is worse at the lower frequency. This agrees with the tsysRatio comparison before and after the horn was installed.  The Src ratio shows TsysB to be higher by 2 to 7 % depending on frequency.
processing: x101/030905/xbCheckCalsx102.pro

05sep03: Tsys vs frequency with the new xband horn.  (top...)

    The xband horn was changed on 04sep03. On 05sep03 tsys vs frequency was measured by firing the high correlated cal and stepping through the frequency range.  The tsys vs frequency with the old horn was taken from the cal measurements done on 06jun03. In both cases: The  differences in the measurements were: The plots show Tsys vs frequency for the two measurements. Something has happened differently for polA and polB between 8 and 9 Ghz. PolB is almost constant at 85% while polA goes from 50% to 85%.  Above 9Ghz the ratios are the same.

I asked electronics if they had done anything with the xband cals. The only thing they could think of was that  they had "cleaned" the cal cables into the dewar on 04sep03.  The performance difference caused by changing the horns should be equal in polA and polB. The amount of cal signal getting into the dewar has probably changed for one of the cal cables so we need to recalibrate them.

processing: x101/030605/tsysVsFreq_hornChange_sep03.pro

jul03 update az,za pointing offsets from calibration scans.  (top...)

    The calibration data taken apr03 thru 21jul03 showed pointing offsets of 8.04 asecs in az and -2.69 asecs in za. These values were subtracted from the current model az,za offsets on 21jul03. The plot shows the pointing errors for apr03 thru 21jul03 before the offsets were changed (the src 3C48 was not included since the tiedown tension were close to zero when the source was measured (10am).

jun03 a1704 recomb lines, gain drifts.  (top...)

    Experiment a1704 was looking at recombination lines in compact hII regions using xband. 5 minute position switching with 1 second dumps were done. During this period the correlator had problems with gain drifts (this problem turned out to be the tubular filters in the correlator).

    While monitoring the xband total power  (25Mhz , 1 second samples) some variations in polB showed up. The plots show  total power vs time for 8 OFF src scans (no continuum). Each plot has the 4 sbc plotted bottom to top (with an offset between sbc for plotting). polA is black while polB is red. The total power has been converted to Kelvins (using the cals) and then the median value for each scan was removed.

When all 4 sbc jump, it is probably not the correlator filters. It is the IFLO before the downstairs mixers, upstairs iflo, or the xband receiver polB.

    The second set of plots has the total power source deflection vs time for the 8 on/off patterns by. For each pattern (on-off) was compute for each 1 second record and then the total power was computed (in Kelvins). The plots show the srcDeflection vs time for the 8 patterns and the frequency of the oscillations.

    If the pointing error is large, the source will be sitting on the steep slope of the beam. Any oscillations in the structure will map directly into a gain oscillation at that frequency. This is what is probably causing the high frequency oscillation.  At the start of each onsrc, the telescope has just complete a move (from the previous off). There will normally be oscillations for a while after this occurs. You can see this in the red and black scans where the oscillations are present at the start of the scans.

    The slower drift may be weather or pointing. If they were pointing errors, then the oscillations that are sitting on top of the slow drift should decrease as the slow drift reaches a maximum (no longer on the edge of the beam). The data doesn't seem to do that. but..It could also be that the oscillations are dying out so that when there are no oscillations it doesn't necessarily  mean that we are on the center of the beam.

processing: usr/a1704/polbjump.pro

jul02 Tsys vs time. Dtsys/Tsys after integration. (top...)

    During jul02 drift scans were done over multiple days. The correlator setup was 50Mhz by 512 Channels, 3 level sampling, 2 polarization's, and 4 frequency channels. The data was sampled at .5 seconds with each drift scan lasting 10 minutes giving 1200 samples per drift. 14 drifts were done per day on the same strip. The data was hanning smoothed. A source was positioned 28 samples in from the start of each drift (it is the spike you see every 1200 samples). Its strength is roughly 1.7 Jy at 8800 (this number not very accurate).
  1. The first plot shows Tsys vs sample for the 1200 samples by 14 drifts. The x axis is a complete set of samples for 1 day. The data has been smoothed by 3 (1.5 seconds) to reduce the size of the plotfile. Each 1200 points, the telescope would move to a new za (rise at the left , transit in the middle , and set on the right). Each color is a separate day (black1, red2, green3..). Each plot of the 4 plots is a separate frequency band. Within a plot, the upper set of lines is pol B (it has a higher Tsys) and the lower set is polA. The numbers 1-14 across the first plot are the 14 drifts done.  Some things to notice are:
  2. The second plot is a blowup of the first showing only the 8750Mhz data with no smoothing. Each day has been offset by 2 K for plotting. You can see that the weather is increasing the tsys by up to 2.5 K or about 5%.
  3. The third set of plots shows spectral density (in units of Tsys) versus strip position and frequency. It has been  averaged over all of the strips off a day, all of the days, and both polarization's. The data has been weighted by 1/sigmaTsys^2 (no weighting for telescope gain was done). For each drift scan:
    After accumulating all of the data, it is multiplied by 1/weights. An average bandpass is divided into this data and channels 50:450 are used to remove any time variation.
     The images have been scaled to 8 Sigma (min to max in the greyscale).  Each image is about 800Kbytes. The rms was computed using strips 100 to 1200 and frequency channels 50 through 450. The expected rms is:

    Where driftsPerDay=14, Ndays=7, npol=2, Han=2, and 3level=1.23 for 3 level sampling.
    Expected rms (7 days): .00028 dTsys/Tsys.

    The measured values were a little less than this (see the plots).

    The 2nd image (at 8800 Mhz) has interference that was there for 2 days. The large drift in frequency may point to a satellite in the sidelobes.

06mar02:HC3N,HC7N in TMC1.  (top...)

    4 5 minute on/offs were done tracking the position ra: 043841,dec:253445 (1950) in TMC1. A1.56 Mhz bandwidth with  1024 channels was used for a velocity resolution of .05 km/sec. The rest frequencies tracked were: 9097.0346, 9098.3321, 9100.2727, and 9024.004 all with a lsr velocity of 5.5 km/sec.Each on,off had a linear baseline removed and then the 4 onoffs were averaged (with no weighting for g/t). The plot shows the line strength of the 4 lines versus the rest frequency and versus lsr velocity. The last plot of HC7N has been smoothed by 11 channels in frequency and velocity. The temperature scale was arrived at by using 45K for Tsys.

21feb02:calibration runs on B0518+165(3C138),B1040+123,and B1328+307(3C286).  (top...)

Calibration runs were done on 3 sources using the standard heiles scans (see stokes calibration). The pointing error and telescope performance are shown in the plots. It can be compared with the 02jan02 data before the horn was moved in focus by .44 inches and the turret position by .35 degrees.
  1. Fig 1. This has the pointing error in arc seconds for the azimuth and zenith angle directions. For the 3 sources there still appears to be an offset. Part of this is do to the calibration scans fitting for the coma while the turret scans don't. This moves the position a little. We also may need more calibration sources to get a better average.
  2. Fig 2. plots the Gain (K/Jy) and Tsys(K), SEFD (Jy/Tsys), and average beam width (asecs) for the 3 sources (different symbols) and the 4 frequencies (different colors).  The SEFD at low za is well behaved (the 02jan02 data used 3C454.3 whose flux is not known but the shape seems to have improved).
  3. Fig 3 shows the coma, 1st sidelobe height, main beam, and then main beam + 1st sidelobe efficiency. The first sidelobe heights has improved by maybe a db from the 02jan02 data.
  4. processing: x101/020221/calib.plot

21feb02:HC3N lines at 9097,9098,9100 Mhz. possible detection?  (top...)

    2 five minute on/offs were done on B0638+095 looking for the HC3N line transitions at 9097,9098, and 9100 Mhz. 12 Khz resolution was used. The onoffs and the polarization's were added. The plot shows the spectral density versus the topocentric frequency. The expected topocentric frequencies are flagged. The spectra has a .011 Kelvins rms. So the 9097 and 9098 lines are a 3 sigma detection (assuming of course that it is supposed to be in emission and not absorption!).

21feb02 beammaps (turret scan) J0237+288  (top...)

    10 beammaps were made near transit of J0237+288 using turret scans. This was after the pointing offsets were updated. The pointing errors for these maps was 1-2 asecs in za and 2->18 asecs in az. The sidelobes are better than the corresponding maps before the offsets were corrected (see the beam maps from 13feb02). The sidelobes now range from 11 to 13 db down. The pointing error for each beam map was: (2,.9,7,5,7,11,10,18,10,12) asecs.
processing: x101/020221/dobeammaps.pro

13feb02 beammaps J2253+161, 3C48.  (top...)

    Beammaps were made of the turret scans on J2253+161 and J0137+331 (3C48). Each source is split up into rise and then set (each ps file is about 3mb..). The color contours are spaced by 3db. The J2253+161 is about 3 times  stronger than 3C48 so the beamaps show more dynamic range. For both sources there is a significant sidelobe on the lower right side. The az pointing errors for these source were large (about a beam) so the turret was off the paraxial rate for the maximum. This may have contributed to this sidelobe. The setting az error for 3C48 got up to  55 asecs so sidelobe should have been worse here. We can check this by redoing the strips after the pointing offset is updated and see if the sidelobe decreases.
  • J2253+161 rise beammaps
  • J2253+161 set beammaps
  • J0137+331 (3C48) rise beammaps
  • J0137+331 (3C48) set beammaps
  • processing x101/020213/dobeammaps.pro

    13feb02 pointing, beam squint, sefd, and beammaps. 3C48, J2253+161  (top...)

        The turret position was moved by .35 degrees and the horn was moved up by .44 degrees from the horn survey. The pointing model was switched to model13 with a "best guess" of the az,za offsets. J2253+161 (3C454), J0137+331  (3C48), and J2123+055 were tracked using turret scans.  The pointing error, squint,Tsys, and sefd are shown in the plots:
    1. Fig 1. The top two plots are the pointing error in az,za versus az and za. This is using model13. The average offset is 27.4 asecs in az and 5.3 asecs in za. The model13 offset for xband will be updated by this amount. The bottom plot is the beam squint (pointErr PolA-PolB). It less than an arc second.
    2. Fig 2. top is the normalized Tsys for polA (black) and polB (red). I normalized the curves by dividing by the average Tsys 0 to 12 degrees. Jumps in the plot may be from the fits or any gain changes (I assumed the gain remained constant for the entire set of observations). Apart from the jumps, tsys is relatively flat out to 15 degrees (unlike some receivers that show a linear ramp at low za).
    3. Fig 2 center is the source deflection (as a % of Tsys for the 3 sources). The large hook for J2253+161 below 5 deg za is from the prf errors (see the next plot).
    4. Fig 2 bottom is the SEFD versus za. 3C48 is the only source of the 3 with a well known flux (the other two are flat spectrum and probably variable). The fluxes used in K/Jy are next to the source names. The best value for 3C48 is 15 Jy/Tsys. With a 45 K Tsys this gives a best of 3 K/Jy gain. The pointing error of almost a beam will cause the gain to be down by  .5 to 1 db.  We will get this back when the pointing offsets are updated.

    02jan02 xband calibration run on J2253+161,3C48  (top...)

        3C48 and J2253+161 were tracked using the standard calibration routine (heiles scans). The plots show:
    1. Fig 1. top is the Gain in K/Jy. The flux for B2253+158 (3C454.3) is probably off by up to 30 %. The next plots show the Tsys, SEFD, and average beam width.

    2. Fig 2. top is the coma parameter that measures the asymmetry of the main beam. The next plot is the peak of the 1st sidelobe, followed by the main beam, and then the main beam plus 1st side lobe beam efficiencies.

    27dec01 beammaps of J2253+161: (top...)

        After the heating resistor was added to the waveguide, J2252+161 was tracked doing turret scans from za=9.8 to 19.2 degrees. Contour maps where made of each 2 minute strips of data. The contour maps are 3 arc minute square (the x axis is labeled with the turret motion rather than the azimuth offsets). Each colored contour is separated by 3db. I used the simple contour filling algorithm which makes smaller files, but gets a little confused with the colors. The edge of the inner most color is 3db down from the peak. The best sidelobe is about 9 db down and is always to the right side in azimuth. The coma lobe is opposite this and gets worse as we go up in za (since the pitch,roll are increasing).

    Pointing error and beam widths from turret scans: (top...)

        Pointing runs using turret scans were run on 25dec01 and 27dec01 using the xband receiver at 8.8 Ghz. 500 MHz was detected about this frequency. The first 5 sources (on 25dec01) were taken before the heater was installed on the wave guide so there was condensation in the horn (and a high Tsys). The signal to noise was not great. Fits with beam widths below 30 arc seconds are above 55 arc seconds were excluded from the data. The pnterr,beamwidth figures show the results:
    1. Figure 1 plots the za error versus za and azimuth.
    2. Figure 2 is the az error versus za and azimuth.
    3. Figure 3 is the total error (az and za) added in quadrature and plotted versus za and azimuth.
    4. Figure 4 is the beam widths in the za (top) and azimuth directions.
        The zaError versus za increased linearly above za of 10 degrees for all sources. This is also the region where the pitch error increases linearly. The beam maps above show that the coma is in the uphill direction or positive za. There is no coma term in the fit, so it is biasing the 2-d gaussian uphill.
        There is not enough data, but it looks like there might be a large 1 azimuth term in the za and az errors.
        The beam width for the za direction is close to the value expected. Scaling from the measured za beam widths at sband, the xband beam width should be 35.6 arc seconds. The az beam width of 40 arc seconds is too large by 25 %. This is larger than the 10% az beam width discrepancy measured at sband.

    First (out of focus) light B1611+343:  (top...)

        B1611+343 was our first shot at tracking a source with the xband receiver. Turret scans were used to measure the pointing error, gain, and SEFD. The conditions were not ideal:
  • The tiedowns were not working so the platform was 2.5 inches low.
  • The source didn't come below 15 degrees za so the pitch, roll, and focus errors were large.
  • The source has a flat spectrum and is a low frequency variable so the flux is not real accurate.
  • The horn location still needs to be surveyed into position with the theodolite.
  • In spite of all of these "shortcomings"  there was still something to see at 8800 Mhz.
  • SEFD, Gain, and Pointing error. The flux used was 4 Jy at 8800 Mhz. The gain was computed using the source deflection/TsysDeflection and Tsys of 43K and 48K for polA and polB (taken from the tsys plots above). The pitch and roll error added in quadrature is probably close to .2 degrees. At 10 Ghz this would cause a 3db gain loss. The focus error is around 1"  which probably contributes a db. A 2 mm rms reflector surface would reduce the gain at 8800 MHz to 58% of theoretical. The pointing error on page 2 is about 38 asecs in az and 18 asecs in za. These offsets can be added to the xband pointing model offsets.
  • PolA beammaps of B1611+343. Each contour map is a 2 minute turret scan integration. The dome moves along the y axis +/- 1.5 arc minutes. The x axis is +/- 2 turret degrees (+/- 1.5 arc minutes on the sky). The contour colors are spaced by 3 db. The azimuth and zenith angle  is plotted at the top of each map
  • processing: x101/011220/doitcals.pro

    20dec01: The cal values and Tsys versus frequency: (top...)

        Tsys versus frequency for the xband receiver was measured by tracking blank sky  and taking data with the correlator while the cals were fired. Tsys was computed as CalOffDeflection/(CalOnDeflection-CalOffDeflection) * CalInKelvins.  The frequency was stepped from 7800 to 9800 Mhz. This cycle was repeated 4 times. The figures show the cal value and Tsys versus frequency:
    1. Figure 1 plots the cal values versus versus frequency for all of the cal types. The values were measured on the receiver range using liquid nitrogen as the load. The top plot is the low cals while the bottom plot shows the high cal values.
    2. Figure 2 is Tsys versus frequency. Black is polA while red is polB. The telescope zenith angle varied from 12.5 to 9 degrees. At each frequency there are 4 separate measurements (*) plotted on top of each other.
        There was interference around 9450 Mhz. Each frequency has four * plotted for the 4 separate measurements (separated by about 5 minutes). There is no scattered in the measurements so the rfi does not look like it made any difference. The rise starting at 9500 Mhz may be partly do to the fiber optic transmitter adding to Tsys because of the IF signals low spectral density.

    20dec01: Power levels in the upstairs if/lo: (top...)

        The IF signal is sent from the platform to the control room via fiber optics. For the transmitter to not add to the system temperature the spectral density of the signal should be greater than -103 dbm/hz.  The FO xmter will start to compress around 0 to 5 dbm total power. Blank sky was tracked around 10 degrees zenith angle and the power at the input to the fiber optic transmitter was measured versus frequency. The IF1 power levels are shown in the figures:
  • The top plot is the total power versus frequency at the input to the fiber optic transmitter with all of the adjustable attenuation removed (11 db before the mixer, 11 db after the mixer). The horizontal line is the total power level to give -103dbm/hz over 1 ghz bandwidth.
  • The middle plot is the gain needed in the postamps to bring the power levels up to -103dbm/hz at the FO xmter and still have 6 db attenuation in the rf attenuator (to allow for some adjustment). The spectral density was computed from the total power by assuming 1 Ghz of constant spectral density about each total power measurement. This will underestimate the spectral density on the edges (since there is not 1 Ghz of total power).
  • The bottom plot shows the power levels at the input to the IF1 mixer chassis if 12 db gain is added to the postamps. It assumes a 35 db gain for the mixer chassis.
  • 12 db seems like a reasonable gain to insert. Larger gain could be used by increasing the programmable attenuation (as long as you don't lose to much head room in dynamic range on the amps/mixer chassis). With the current setup the  the system temperature for the higher frequencies (9.5->10Ghz) is probably being increased because of the fiber optic transmitter noise level. At the top side there will probably be 15 do 20 db of headroom before the fiber optic xmter begins to compress.

    Rfi seen using the xband feed: (top...)

        After the feed was installed an rfi monitoring session was run using the xband receiver on the telescope. This lasted for about 2 hours (11 am to 1 pm). 60 1 second  integrations were done at 100 Mhz intervals with a resolution of 25Mhz/1024 channels. There were  three 60 second runs  (spaced by about 40 minutes) at each frequency. Interference was seen in two of the 100 Mhz bands. A peak hold spectra was made for these two bands (taking the maximum value in each frequency bin over the 180 samples). This is the worst the rfi got in a 1 second integration. Images of time versus frequency of the spectral density were also made. Each image was normalized to the median spectrum over the 180 samples. The figures are:
  • Peak spectral density versus frequency for the two bands with rfi. The vertical scale is linear in power. Red is polA and green is polB.
  • Spectral density image at 8120 Mhz (time versus frequency).
  • Spectral density image at 9350 Mhz (time versus frequency).
  • The images have been normalized to the median spectra over the 180 samples. They show the time variability of the rfi.
        processing: x101/011219/rfi.pro

    19dec01: Measuring the turret position of the feed: (top...)

        The turret position of the feed is measured by moving the  turret in a sine wave above the tertiary while tracking blank sky with the telescope. It turns out that the peak of the power corresponds to the turret focus position (this has been verified by surveying the resultant positions of other feeds). You would expect the turret position for focus to correspond to a minimum in power since the sky is the coldest thing around. This peak may result from the match of the horn into the tertiary maximizing the transmitted power into the receiver at the focus (thermodynamic arguments aside..).  Figure shows 2 sets of turret swings using a sine wave with amplitude 8 turret degrees and period of 15 seconds. Each measurement lasted for 2 minutes. The top two plots are polA and the bottom two are polB. A fifth order polynomial was fit to the data and then the peak was flagged. The two polA swings and the two polB swings agreed to .001 degrees. The polA swings differed from the polB swings by .17 turret degrees (45 sky arc seconds per turret degree). This disagreement could be a delay difference in the A, B channels (The time constants in the square law detectors were set to .02 seconds). I used the average of: 161.99 as the turret position for xband.
        processing: x101/011219/doitri.pro