cb (5-6 ghz) az swings 28aug12
last updated 06apr13
Azimuth swings were done with the cband receiver on 28aug12.
The setup was:
The data processing for each box:
- az 270-630 and back at +/- .4deg/sec
- clear sky, data taken around 11am.
- dome at za=15deg
- mock spectrometer with 7 boxes covered 5 to 6 GHz
- 172MHz bw, 8192 channels per box
- .1 sec sampling (averaged to 1 second)
- input the data averaging to 1 second
- interpolate az positions to center of data records.
- Create bandpass correction
- compute total power of each spectra.
- compute median of spectra that belong to the lowest 20% of
the tp above.
- fit a linear polynomial and 35th order harmonic to the
median bandpass. use this as the bandpass correction.
- divide each 1 second spectra by the bandpass correction
- compute the median of each 1 sec spectra and remove it (this
is to get rid of continuum sources).
The images show the dynamic spectra for the Clockwise (CW) and
counter clockwise (CCW) az swings for each 172 MHz band.
Notes on the dynamic spectra:
- Each bandpass is divided by a fit rather than a median
bandpass. This is so we don't cancel out constant
birdies (that may be coming from inside the dome). Because of
this, some artifacts remain in the image.
- the sinx/x birdie at the center of each band is probably
from the mock spectrometer
- The ripples at the edge of the band is from fitting the
- completely dark stripes.
- The bandpass fitting routine throws out outliers. For
really large rfi, they points are thrown out, so the fit is
not constrained at these points (they should be set to some
peak value). Depending on the fit, these values may be
negative or positive.
Birdie power vs azimuth.
Birdies were identified by looking at the
dynamic spectra. The avg power over the birdie bandwidth was
computed and then plotted vs azimuth. The clockwise and counter
clockwise swings were over plotted to see if the birdies repeated
in azimuth (for this to happen then need to be stable in time).