R2696 Lunar Reconnaissance Orbiter
16may12 - run on
14may12 - test
r2696 is doing bi static
sband measurements with AO transmitting and the LRO satellite
receiving the echo from the moon. The experiment setup is:
- a 1.6 MHz chirp 100 useconds long was used. The chirp was
repeated every 625 usecs. (duty cycle of 16%).
- The transmitted signal was then sampled (from the coupler in
- The radar interface (RI) was used. Its setup was:
- The signal was mixed to baseband with the 30 MHz mixers.
- The I and Q signal were each baseband filtered
with a 2. MHz filter.
- the data taking started on a 1 second tick
- data was .2 usec sampled (continuously)
keeping 4bits in I and Q.
14may12: test run
We did a test run on 14may12. The telescope
was at a za of 19.69 since the moon had already set. The transmitter
output was about 200 K Watts.
Plots were made of the recorded Tx
data (.ps) (.pdf):
- Page 1:spectrum, voltage
- top: 30 second average spectrum of chirp
- 160 usecs about each 100 usec chirp was used
- bottom:over plot the i,q voltages for the measured chirp
- .1 seconds (160 ipps) were over plotted. black in I,
red is Q
- Page 2: generate a chirp for pulse compression:
- Top: inphase, bottom: quadrature voltage samples
- The black traces are the measured data.
- The red trace is a generated chirp:
- 100 usecs long, chirping from -.8 to +.8 MHz.
- I only plotted half the chirp (to show more detail).
- Page 3: pulse compression using the generated chirp
- Top the voltage samples after pulse compression. (each point
is .2 usecs).
- I did this for 1000 ipps and then averaged the I and Q
- Bottom: pulse power averaging 1000 ipps.
- The fwhm is about .6 usecs (1/1.6MHz)
- Page 4: phase variation at the compressed peak.
- The phase from the I,Q samples was computed for the
peak voltage (after compression).
- the .625Usec samples were smoothed to 15.6 milliseconds
- The phase varies by 2 or 3 degrees over the 30 seconds of
- Sampled transmitter data didn't show any obvious problems.
- The spectrum of the chirp only showed a few db dip. In
previous runs it had been larger. This may have been a problem
with the leakage signal
- The compressed pulse did not show a signal a 1usec delay
(the dish to platform distance). This had been seen
- with the dome at 19.69 degrees the stw may have been
smaller. We'll see what happens with 16may12 run.
16may12: Run with lro satellite.
On 16may12 we did a run with the lro satellite
receiving the echo off of the moon. Data was taken with the ri (as
described in the intro).
- Data acquisition at AO started at 12:59:59 and went for 50
- Data from the experiment can be
- all 50 minutes is stored in a single file (14 Gbytes).
- The .2 usecs 4bit sampled data (with the ri)
- The headers have been stripped off (leaving just binary
- Look at the Readme file for the file format.
- txPwrMeter.log - log of transmitter power.
- column 1 mjd of sample (every 10 seconds)
- column 2 : power meter sample in dbm
- attenuation factor is 82.8 dbm
- The meter reads average power. The duty cycle was
- Kw=10^(-x.xxx + 82.8 - 30)*.1)/duty Cycle
Processing the sampled chirp:
- 1 second blocks of data (1600 ipps) were input and then
averaged to give 1ipp sec
- 800 samples around the chirped signal were kept (out of the
3125 samples in an ipp).
- We ended up with 2298 seconds (averaged ipps).
Plotting the data:
- Plotting the voltage chirp vs
time (.ps) (.pdf)
- The voltage chirps were averaged to 10 5 minute ipps before
- The 10 5 minute averages were plotted with offsets for
display. The first 5 minutes starts at the bottom (black
- Page 1:
- Top: Inphase voltage vs time
- 2nd: quadrature voltage vs time
- You can see that the shape is changing with time.
- 3rd: Inphase voltage. blowup 35 usecs around where the
chirp goes through 0hz.
- bottom: Quadrature voltage. blowup 35 usecs around where
the chirps goes through 0 hz.
- Vertical lines are plotted at the peaks (in I and Q) for
the first 5 minute average.
- You can see that the peak is not remaining in the same
time slot for the 5 minutes.
- It moves by about 1.2 usecs over the 50 minutes. +/-
freq both move away from DC.
- This is not a sampling problem since that would have +/-
freq move in the same direction.
- This could be the bandwidth of the chirp generator
changing with time. We checked the generator the next day
and the 10MHz reference was plugged into it.
- Dana pointed out that this could also be a phase change
in the signal or an lo (probably the signal).
- Page 2: Plot the start and end of the chirp
- 1,2: start of chirp for I and Q
- These look pretty stable for the 50 minutes
- 3,4: end of chirp for I and Q.
- These look like they may have moved by on .2 usec
- Plotting the phase drift vs
time (.ps) (.pdf)
- Page 1: How the average phase of the chirps changes with
- Top: Voltage chirp averaged over 50 minutes (voltage i,q)
- Bottom : The average phase (over the entire chirp) vs time
for the 50 minutes,.
- The phase was computed for each sample of the chirp
using the 1 second averaged chirps.
- This was done for each of the 3000 1 second averages.
- for each channel (in the chirp) phase jumps were
- The average phase (over the chirp) was then computed for
each 1 sec averaged sample
- The jumps in the chirp occur at 66 to 76 second
- Page 2:. How the phase of the chirp changes across the chirp
and with time.
- The 1 second chirp phases were averaged to 1 minute
- The phase as the first minute was subtracted from the
other 49 minutes. this was to remove the phase across the
- The 50 1 minutes phase averages were then overplotted
(with no offsets)
- The plot shows the change in phase of each channel with
time relative to the start of the run.
- The top strip is the start of the experiment.
- Plotting the average spectra
of the sampled chirp (.ps) (.pdf)
- The ipps were average to 5 minutes before computing the
- Top: Average spectra spaced every 5 minutes. Offsets have
been added for display. Time starts at the bottom (black).
- There is a glitch at DC in the spectra at the bottom. This
goes away at the end of the run.
- Bottom: blowup of average spectra around DC.
- The power increases and then goes close to 0.
- The dashed horizontal lines show the 0 power baseline.
- After looking at the data from the start of the run i
thought that the signal was AC coupled somewhere (it isn't)
- After plotting all the data you can see that it is not AC
coupled (unless it is changing with time!).
- Dana pointed out that this could come from our fixed 20
MHz leaking into the chirped 20 MHz.
- The chirped signal is +/-.8 MHz about 20MHz. So DC maps
- there is a switch that sends our 20 MHz (from our dds )
or the chirped 20 MHz to the transmitter.
- If there is some leakage through this switch,then when
the chirp passes through 20 MHz you would have AO
and LRO signals beating together. If the phase of these
two changed with time you could have the dc component go
from 0 to some larger than normal value.
- Find out where the 66-76 second glitches are coming
from. Dana and ganesh thought that ron may have seen this
- Check the synth switch down in the control room to see what
kind of leakage there is.
- Measure the phase drift in our system during the day while
moving the azimuth and za.
- Take some data directly from the lro chirp generator (probably
want to run it at 30 MHz to use our baseband mixers.
- See if we still see the chirp changing over time.
06aug12 test run
We did a test where lro generator was sampled
by the ri (the sband transmitter was off). The setup was:
- The lro generator 20 Mhz output was upconverted to 30 Mhz and
then downconverted and sampled by the ri.
- Signal path:
- lro output -> balanced mixer to 30Mhz -> 30Mhz ifAmp
-> 30Mhz complex mixer -> 2MHz baseband filter on I
and Q -> opamps -> scope -> RI.
- The base band signal was set to about +/- 2.5 Volts
peak to peak (RI is +/- 2.5 volt input).
- RI setup:
- .2 usec sampling, 4 bits, start on 10 sec tick, 1
buf/ipp, 10000 usec/ipp, 50000 samples/ipp.
- data was written via gio to
- The lro stepped through the following sets of pri's spending
about 5 secs at each:
- 525,1600,850,1000,1150,1300,1450,1750,1900,1600 usecs.