p2717 pulsar search taken 26jun13
p2717 took data with the 327 receiver and the puppi
backend on 26jun13. The setup was:
- 327 receiver
- puppi with 68.75 MHz bw (2816 channels), polarizations
added, 81.925 usecs integration per spectra,
incoherent search mode, 8 bit data recorded.
- 15 files were taken with puppi scan numbers: 0174 to 0189
(scan 184 is missing).
- file 1, scan 174 had 60 seconds of data (on pulsar
- files 2-15, scans 175-189 had 15 minutes of data
- For these files i used the last 46.29 seconds of data (the
2nd 1.5 gbyte file of the 15 minutes)
Average and rms/mean of spectra
The average spectra and rms/mean was computed
for each row of the first fits file (scan 174)
The plots show the average
spectra and rms/mean by channel for file 1 (.pdf):
- I think that the puppi input data was adjusted to have a sigma
of 20 counts.
- Each row in the fits file contained 8192 81 usec spectra
(.671 seconds of data total).
- There were 90 rows in the file.
- The average spectra were computed by averaging the 8192
spectra of each row (giving 90 .671 sec averaged spectra)
- The rms/mean by channel was computed for each row
- The rms was computed for the 8192 samples for each channel
and then divided by the mean value.
- The rms/mean should match the radiometer equation:
- The factor of 2 comes from polarization adding.
- Top : average spectra for each row (.671 seconds) are over
- The vertical scale is 8 bit counts of the output spectra.
The average value of the spectra is around 10-15 counts
- The filter shape comes from the 52 MHz rf filter and the
from the 60 MHz IF filter (which has steeper edges).
- Bottom: rms/mean for each channel.
- The rms was computed along each channel of the 8192 spectra
of each row.
- This data has 81.925 usecs time resolution and .0.024
frequency resolution (assuming rectangular filters)
- The rms is divided by the mean value of each channel. The
value of this plot should correspond to the radiometer
- deltaT/T= 1./sqrt(bw*time)
- bw=0.024414062E6 hz
- time= 81.925E-6 secs * 2
- (times 2 since we've added the polarizations
- The red dashed line shows the expected rms/mean the
bandwidth and integration time of the data.
- The measured value may be a bit higher that the computed
values because the polyphase fitlerbank may make the filters
a bit narrower.
- The spectralMean* (rms/mean) give the number of counts
of noise in each channel.
- For the center of the noise on top of the spectra has
about 8 counts (15*.53).
- Towards the edge of the band the noise has about
(2*.6)=1.2 counts. This will start to add some noise to any
spectra bandpass correction:median vs Fit.
Dynamic spectra were made of the 90 averaged
spectra (.671 secs each). The image was flattened by:
a 10 sec period was seen at (353.16-353.55MHz) in file 1.
Dynamic spectra of files 1-15
spectra were computed for each file using the.671 sec averaged
spectra. 5 files at a time were then combined into a single image
with solid lines horizontal lines between each file. The files in
the image are loaded from the bottom up (file 1 the bottom,file 5 at
- Mean values:
- center of the band has about 15 counts (out of 255).
- edge of the band gets down to 1 or 2 counts
- Counts on the noise:
- Center of band about 8 counts
- edge of the band gets down to 1 or two counts
- The rms/mean for each channel is close to the expected value
(from the radiometer equation).
- The bandpass shape is probably being determined by the 60 MHz
narrow band IF filter.
- Bandpass correction:
- The median bandpass does a good job of flattening
dynamic spectra, but constant rfi gets removed
- Fitting a harmonic function to the median spectra and using
that for the bandpass correction will not remove constant rfi
(but it doesn't do as good a job flattening the image).
10 second period
|seen in all 15 files
pulse length about 160 millisecs
sweeps from 360 to 353 MHz at start of pulse
sweep rate -.00189 MHz/usec
Value is probably overflowing the 8bit number
|shows up with 353 in
|show up together with
10 sec period in file 12
|file 12 10 sec period.
Pulse arrives a little before 353.1
|fm station harmonics
|3rd harmonic of 102.9
|3rd harmonic of 104.1
|this is the difference
between 102.9-104.1 probably intermods. The towers are
about 100 meters apart (more info)
|AcUnits building 1
|ac unit atop building
1. Probably a lot more
|AC unit on top
|lots of birdies
- It will probably be hard to excise the 10 sec rfi completely
because of the wide sweep at the beginning of each pulse. This
looks like an oscillator or phase locked loop that is not doing