p1693 total power dropouts, rfi
- high freq resolution data taken 27feb14 showed that the
receiver is not going into compression. The power dips occur
because the rfi is jumping in frequency for a few 100 millisecs.
During the jump, the power level of the rfi goes down. (more
p1693 took 327 pulsar search data during the main
cable 8-4 repair. The data from 20feb14 (after midnite) showed (what
appeared to be ) total power dropouts:
- pulsar search data was taken with the 327 receiver and the
mock spectrometer. cfr: 327 Mhz.
- bandwidth: 57.344 Mhz, 1024 channels, sample time: 125
usecs,16 bit, polA,polB summed in mocks
- The project takes scans that last for 1 hour.
- The data after midnight 20feb14 started at 00:48.
- The first 2 gbyte file of each scan was processed (129
secs/file). There are 7 files starting at:
- 00:48, 01:48, 02:48, .. 06:48
- For each file
- the total power was computed (at 125 usec resolution) and
then smoothed to 1.25 millisecs
- the spectra were averaged to 1 second resolution.
The plots show 10
secs of total power data for the start of each of the
7 files (.ps) (.pdf):
- Total power was computed over the 57 Mhz.
- The data was smoothed to 1.4 milliseconds
- Page 1: file 00000.
- 00:48 ast
- Top: total power vs time.
- the red vertical lines are my estimates (rough) of the
start of each dropout.
- Time difference between adjacent dropouts (time between
red dashed lines in top frame).
- Page 2-4. total power vs time for files 100 -> 700.
- the dropouts became weaker, and then returned in file 500.
Dynamic spectra using the 6 files
Dynamic spectra were made using the 1 second
averaged spectra from files 00000 .. 0600 (7*129 makes an image a
little too big for my display).
The processing was:
the image shows the dynamic
spectra for the 6 files (.gif)
- Normalize the 129 spectra of each file to the median value (a
single value, not a bandpass correction).
- Bandpass correct all 6*129 spectra by computing the median
spectra for the combined files
- You can see the steps between each 129 file (they are
separated by 1 hour in time).
- the 3rd harmonics of the fm stations are clearly seen:
(102.9,104.1,107.3)*3=308.7, 312.3, 321.9
- The rfi at 322.5 is drifting in frequency.
- The 10 sec periodic signal is at 352 and 354 Mhz
- The 3rd group from the bottom has a baseline with lots of
ripple in it.
- it had an ra,dec of around 12:35:40, 10:51:13
- dropouts were seen in the total power.
- The decrease was about 1% of Tsys.
- the spacing between the dropouts alternated between 1.42 and
- I looked at the a/d blanking.. there was none during this
- the plots show that the dropouts changed over hours. They were
strong at 00:48 and 05:48