14feb12 puppi first light with lband
Search data was taken with puppi and lbw on 14feb12.
The setup was:
- lbw recieiver in linear mode
- Tracking J2017+0603.
- IF to puppi : 1000 to 1600 (1180 to 1780 Mhz). 1200 Mhz IF
centered at 1380 Mhz.
- 800 Mhz search mode using second nyquist band.
- 2048 channels, spectral integration 40.96 usecs.
- 53.7 seconds of data (1 11gb file) was processed:
- 4096 (40.96usec) spectra/row in fits file
- 1 row=.167 seconds
- 71 rows in file
plots and images.
The plots/ images show some results from the observation:
- all data: Avg spectra,
rms/mean by channel (.ps) (.pdf)
- Page 1: average specgtrum
- Top: Stokes I
- Bottom:PolA(Black), polB (red)
- The horizontal axis is sky frequency.
- The falloff at 1120 Mhz is the bandpass filter for lband
- There might be a 31 Mhz Ripple in the spectra.
- If this is a cable reflection then:
- 1./31Mhz * 150 Meter/usec * .7(velInCable) = 3.4
meters or about 11 feet.. So probably not the cable from
the receiver room to puppi (although it probably
wouldn't hurt to check it).
- :Page 2: rms/mean by frequency
- For each row (4096 spectra) the rms is computed along each
channel and then divided by the mean value (Tsys).
- Top: rms/mean for each row then average the 71 rms/means
for the file
- The horizontal red dashed line is the expected
rms/mean from the radiometer equation.
- The vertical dashed lines show various rfi sources:
- Black: punta salinas radar in mode A (more
- Red remy radar (1270,1290) (more
- green: FAA radar(1330, 1350) (more
- blue Iridium satellite (more info)
- Light brown: band edges from lbw bandpass filter.
- rms/mean for each row over plotted (with offsets) for 12
seconds of data.
- You can see the punta salinas radar (1230,1250)
blank its transmitter when it points at us (3-5 seconds)
- There are a few rows who have spike all across the band
(6.5 light blue, 8 secs red). This is probably the
digitizer or butterflys of the polyphase filter bank
- Dynamic spectra
for row 38 (6.4 seconds) showing radar pulses (.gif)
- This shows the dynamic spectra for the 4096 spectra in
row 38 of the 1st file (6.4 lite blue trace that showed spikes
across the entire band).
- It covers 167 milliseconds.
- horizontal lines of power start appearing at 20
milliseconds and last till about 120 milliseconds.
- The vertical pulses near 1620 are iridium satellite. The
spacing on the lower, and middle pulses is 90 milliseconds.
This is iridiums basic cycle (45 milliseconds uplink,45
- Row 38 total power vs time
showing radar pulses (.ps) (.pdf)
- Top: Total power vs time for the 4096 spectra in row 38
(lite blue line with spikes in rms/mean plots).
- You see the radar beam sweep through arecibo during its 12
second rotation period.
- The individual spikes are the radar Ipp (Inter Pulse
Period of 2.5 to 3.5 milliseconds).
- Bottom: The time difference between adjacent radar spikes
- The FAA radar uses 5 ipps to get around range aliasing:
- 2.633,2.821,2.74596,2.594.84,3.330996 milliseconds
- The colored dashed lines are the 5 ipps used by the FAA
- The Lineup shows that these total power spikes (or
horizontal lines in the spectra) are coming from the
1330,1350 faa airport radar.
- I'm a little surprised that there isn't a larger spike in
the spectra around 1330, 1350. It may just be the way the
image is scaled.
- Image of rms/mean for
the 53 second observation (.gif)
- the rms/mean for each row (4096 spectra) was computed. The
320 of these (during the 53 sec file) where then made into and
- Since the rms/mean was done for each channel, there was no
need for a bandpass correction.
- The image was scaled to emphasize the rfi.
- 1232-1255 - punta salinas.
- You see many 12 second radar rotations with blanking
whenever they point at AO.
- 1500-1530 looks like an image of the 1232-1255. This
occurs right before and right after blanking (when
there beam is close to pointing at AO).It's [probably
happening in the analog if/lo.
- 1270,1290 - remy radar.
- every 12 seconds (starting at 7.5 seconds) you see the
line fatten and a horizontal line of spikes occur across the
entire band. This is when the radar is pointing at AO.
- 1330,1350 - faa radar.
- Creating spike across the band every 12 seconds when the
radar points at AO.
- 1/2 way between when the radar points at ao, there are a
set of widely spaced spikes that last for about 2 seconds
- 1409,1428 at 12-13 seconds, 1530,1560,
- The are either the horn spillover on the primary when
the radar points away from us, or it is a plane that is
passing by. If it is a plane, then the position in
time will change. These look more like some intermods in
the analog system.;
- Image of
rms/mean for 53 second observation scaled to see weaker
- This image is the same as the previous. It uses histogram
equalization for the scaling.
- Need to check if some of the bandpass ripples are coming from
- The noise strength is following the radiometer equation
(at least at the 40 usec level..).
- The FAA, and Remy radar are causing spikes throughout the
spectrum when the radar points at AO.
- The online monitoring was showing min,max spikes across the
spectra. They are probably coming from these rows when the
radar points at AO.
- This is either the A/D or (more probably) overflows in
the butterflys for the fft.
- changing the down shift rate in the butterflies (form
0xaaaaaaaa) to more shifts could help
- in the butterflies, noise grows as sqrt(N) where N is
the number of butterflies done. For sine waves or radars,
it grows as N.
- If more downshifts are done, then the 8 bits that
are extracted from the 18 bits of the fpga may need to be
- This test used 2048 channels and incoherent spectra. For
coherent dedispersion the fft length is shorter (512) so
there are fewer butterflies used. This should help this
- The rms noise was set to around 22 counts. You could
lower this a little without hitting the
digitization noise threshold.
- We need to measure the max input voltage at the A/D to see
if the A/D is getting zappped.
- The radars are also causing intermods that look like they are
coming from the if/lo. Need to check if the two amps before
puppi's a/d have enough dynamic range.
- Since there is only one analog mixing stage we can probably
predict where these should show up in the 1-2 ghz IF or
from the digitizer.
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