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 t
he
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