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Intro

   The  xband receiver on the p12m telescope was monitored for 7 hours on 08jun21. The setup was:

• The telescope tracked blank sky (ra 07:00:00 dec 16:00:00) for 7 hours starting at 8:30.
• We  were pointing south of zenith.  The ra of the sun was about 22deg dec.
  
• We used the xband receiver using 8050 to 9200 MHz
• Mock spectrometer used to record the data.
• 7 172 MHz bands centered at:
  
• 8132,8296,8460,8624,8788,8952,9116
• Each band spaced by 164 MHz
• 2 pols, 4096 channels/pol, 42 KHz channel width
• spectra dumped once a second
• The datataking sequence was:
• 300secs  data
• 10 sec cal on
• 10 sec cal off
• repeat sequence
• We covered elevations 10 to 87.6 degrees.
• We wanted to measure Tsys vs elevation using the cal diodes.
• We do not yet have accurate measurements of the cal across freq
• So i used the enr of the diode and losses of the cables and cal coupler.
• I ended up with a cal of 43K. This value was used across all freq and both pols.
• -->These cal values are just an estimate. The Tsys values computed from the cals should be take with a grain of salt.
• During the test there were heavy clouds and 2 periods of rain.
• What we ended up measuring were problems in the system.
  

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Processing the data

• The total power was computed using the entire spectral band. No rfi removal was attempted.
• The total power was normalized to data taken 11 to 12 hours (when there were fewer clouds).
• So the units would be Tsys.
  
• The total power vs time for each frequency band was normalized  to the average of the first 1000 points taken (so the units become Tsys).

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Plotting the data

    The first plot shows the total power vs hour of day (.ps) (.pdf)

• Top: total power vs  hour of day for polA.
• Each color is a separate 172Mhz frequency band
• The different bands responded similarly.
• The narrow spikes are the 10sec calon, caloff
• The power at  12.5 and 13.5 to 15:00 are  rain,cloud
• Middle:total power vs hour of  day for  polB.
• The cal input to polA and polB has similar power.
• The polB caldeflection being smaller than polA --> that tsys PolB is higher than polA
• During the power increases at 12.5 and 13.5 ->15 (rain,,clouds) the cal deflections are not seen.
• Bottom. Elevation vs hour of  day
• This shows the elevation we tracked.

    The second plot includes the rainfall and size of the cal deflection (.ps) (.pdf)

• Page 1: total power and rainfall vs hour of day
• Top: total power vs hour of day and rainfall
• The uses the 8624 Mhz band for the total power.
• Black:polA , red:PolB
• Green is the rainRate in inches/second
• Blue is the cumulative rainfall for the day (in inches)
• The rain monitor is located at the lidar lab (a  few 1000 ft from the 12 meter)
• Bottom: blowup showing the period of rain.
• The large increase in Tsys coming from clouds and rain
• For polA Tsys is more than doubling.
  
• for polB you see no cal deflection during the rainfall period.
• The purple dashed line shows that polB power never got above this level.
• Page 2: tsys in kelvins and the size of the cal deflection.
• Top: Tsys vs hour of day
• I used 43K for the cal
  
• polB is much higher than polA (although Tcal needs to be measured more accurately).
• During the rainfall, Tsys goes off scale. Since the cal deflection goes to 0 , tsys will get really large.
• Middle: caldeflection vs hour of day.
• The units are spectrometer counts. The attenuation was not changed during this period.
• Changes in the electronic gain of the system will cause the values to change.
• During the rain periods
• PolA cal deflection gets noisy. This is expected since tsys is probably changing.
• PolB cal deflection goes toward 0 during the rain periods.
• Bottom: Cal deflection vs Tsys value cal off.
• The horizontal axis is the cal off tsys value  in spectrometer counts.
• PolA values are smaller that polB.. part of this is that the electronic gains were different.
• The vertical axis is the cal deflection in spectrometer units.
• polA has a  slight downward trend with increasing power.
• Polb caldeflection  goes to 0 as the tsys power increases.
• The polB chain is going into saturation. It is actually hitting the voltage rail of an amp somewhere.

SUMMARY:

• We were not able to measure Tsys vs elevation because of the clouds/rain.
• We found that polB is going into total saturation  with the increase in temp from clouds/rain..
  
• PolA increased by 3db. so the temp for polB was probably similar.
• We need to find out where the saturation is occurring.
• Measured power levels  shows the power levels that the system runs under (although it was a clear day:)
• fiber optics rcver output : -27,-31 dbm . well below the 10dbm saturation of the link
• lna: output around -35dbm
  
• amp in hub : around  -15dbm
• input to postamp chassis: -26dbm
• after first amp in postamp chassis: +2dbm (2 db compression 16dbm).
  
• filter,2nd amp output: -8.3dbm
• diplexor input: -10dbm
• All of these values are way below saturation.
• One thing we've noticed is that most of the power coming out of the lna is around 4.5 GHz.
• we need to check if this can actually get through  the waveguide cutoff (probably the circular part, especially with the dielectric  rod in the center.
• The plot shows polB, but polA has a similar output.
  
• We need to figure out where this extra power is coming from.
• If this is the problem, why is polB  saturating and not  polA?
• It would be a great help if we could purchase a cal kit for the xband waveguide so we could use the transitions to see what is going on inside the waveguide . Unfortunately we've been told there are no funds to do this.. so i guess we'll have to continue messing around trying indirect tests.
  

processing:x101/210608/tsysvsel.pro