radar 4bit time domain sampling. 30Mhz IF input

dec13


links:
 the 4 bit histograms for all of the tests (.ps) (.pdf):
the results of each run followed by a simulation for that run (.ps) (.pdf)
the results for the runs whose output rms was close to the optimum value (.ps) (.pdf)

Sections:


running the tests
looking at the data
Summary


  Intro:  (top)

   See radar datataking with pdev  for a description of how the datataking works.
  • 4 bit data was taken with different input rms voltages, decimations, and shifts.
  • Histograms were made of each dataset
  • rms results for all runs as well as a comparison of simulated runs were made.
  • For those runs with 4bit rms close to optimum, the results were displayed as well had plots of the average bandpass.


Running the tests:  (top)

  • 31 different runs were made.
    • for each run, the rms from the scope was recorded
    • I measured a 1.1 db drop scope to mock spectrometer.
    • I varied the input rms voltage, decimation, and shift.
  • The idl routine istat=pdevrmstmd() was used for a quick look at the 4bit rms and the average spectrum.

Looking at the results:  (top)

  • idl was used to look at the data
    • @phil, @pdevinit, @masinit
    • pdevtmdchk() would input the file, compute the rms and various histograms.
  • I was testing various decimation, shifts, and input voltages so the resulting rms was not alway the optimum
    • I also used this data to verify that my 4bit time domain simulator worked.
The first set of plots shows the 4 bit histograms for all of the tests (.ps) (.pdf):
  • Each page shows histograms for a single decimation
  • The colors on a page differentiate the various input Voltages, and shifts
  • The optimum 4bit rms should be 2.98

The 2nd set plots the results of each run followed by a simulation for that run (.ps) (.pdf)
  • Page 1: the results of each run
    • Top: input rms voltage measured at scope
    • 2nd : measured 4bit rms
    • 3rd. Upshift used
    • bottom:decimation used.
  • Page 2: simulation of the runs:
    • Top: measured and simulated rms
      • black is measured
      • red is simulated (with no prefiltering)
      • green: simulation with boxcar smoothing of data before filtering
        • This give a little better match since the input signal was 20-25 MHz wide in a 160 MHz sampling bandwidth.
    • middle: Measured rms/ simulated rms (no prefiltering)
      • the first decimation is low because of the missing power in the input signal
      • the other runs were within 10 % of the measured value.
    • Bottom: measured rms/simulated rms (prefilter by 3)
      • This does a little better job of matching the input at dec=5.
The last plots show the results for the runs whose output rms was close to the optimum value (.ps) (.pdf)
  • All of these had 4bit rms's within 10% of the optimum.
  • Top: input voltage for each decimation.
  • 2nd: the measured rms (black). The green line is the simulated value using the measured input parameters.
  • 3rd: the upshift used for the measurements
  • bottom: The input voltage that we should have used to get the optimum 4bit rms for this decimation and shift.
    • Black is the measured values, green is the simulation.

SUMMARY:   (top)

  • radar 4bit time domain IF sampling can be done with the mock spectrometers
  • 12, 16 bits are used through the sampling, mixing, filtering. At the last stage it is clipped to 4 bits
  • The simulator gets within about 10% of the measured values.
  • I/O rates:
    • decimate = 5  (32 MHz bandwidth)
      • 1 pol: 32M Bytes/secs
      • 2 pol: 64 M Bytes/sec
  • The table below shows the  decimations, down shifts, and input voltages that will give the optimum rms for 4 bit sampling:
    •  
    • bandwidth
      MHz
      decimation
      shift
      input Voltage
      Recs/Second
      1pol
      2pol
      32
      5
      13
      .059
      30.52
      61
      20
      8
      12
      .078
      19.07
      38.15
      10
      16
      12
      .055
      9.54
      19.07
      5.16
      31
      11
      .080
      4.92
      9.84
      3.2
      50
      11
      .062
      3.05
      6.10
      1.6
      100
      10
      .083
      1.53
      3.05
      .32
      500
      9
      .075
      .305
      .610
      .156250
      1024
      9
      .054
      .149
      .298

processing: x101/131031/mocktmd.pro, tmdplothist.pro,goodsettings.pro

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