Sections:
Intro
Setup
Processing the data
Dynamic spectra of the azimuth swings
Average/PeakHold spectra for each az swing:
The azimuth dependence of all the birdies
birdies with no az dependence (coming from dome)
birdies with common az dependence
Summary
other: azswings done 09mar11

Introduction (top)

The setup:

• 327 Mhz receiver. 750Mhz IF
• azswings 270 to 630 degs and back at .35 degs/sec
• mock spectrometers:
• 7 spectrometers cover 300 to 350 Mhz.
• Spectrometer cfr, 304,311,318,325,332,339,346 Mhz
• + 5 MHz added in iflo menu, -5 Mhz added in mock digital mixer.. to move DC spikes out of band
• 8 Mhz bandwidth, 8192 channels; 976 hz resolution, 1 second sampling (about 1 sec)
• The alfa motor controller and the dome cameras were turned off for the azimuth swings.
  

Processing the data: (top)

• For each azimuth swing a bandpass was constructed from the 1027 spectra. A fit to a bandpass was needed rather than an average since some rfi are constant and would remain in the bandpass average. The bandpass was created by:
• Compute a median bandpass from the 1027 spectra.
  
• Fit a 20th order harmonic and a linear polynomial to this median bandpass using robfit_polyfft(). This iterates the fit throwing out outliers.
• Divide each of the 1027 spectra by this fitted bandpass. This should remove most of the bandpass.
• For each spectra compute the median total power and subtract it. This should remove the source contribution.
• PolA and polB were then averaged.

Dynamic spectra of the azimuth swings:  (top)

• Some of the birdies have an azimuth dependence. This means that they are coming from outside the dome
• A number of these came from 3rd harmonics of 102.9,104.1, 107.3, and intermods between 102.9 and 104.1 (these towers are located within 100 meters of each other).  (more info from 09mar11 azswings)
  
• Other biridies have no azimuth dependence. This tell us that they are probably coming from inside the gregorian dome.

Plots of the rfi

• all 7 bands were combined into a single spectra (976 Hz resolution, 50Mhz).
  
• The top two frames show the average of each azimuth swing:
• black is CW azswing, red is the CCW swing.
• This average over 1027 seconds.
• Topframe: vertical scale 0 to 10*Tsys
• 2nd frame: vertical scale 0 to 1*Tsys
• The bottom two frames are a peak hold for each swing
• frame 3: vertical scale 0 to 10*Tsys
• frame 4:  verical scal 0 to 1*Tsys.

• I went through and selected 140 different birdies.
• they had to stick up at least .2*Tsys (in 976 hz channels, 1 second integration).
  
• I left out some of the wider rfi (3rd harmonics of fm stations and their intermods)
• This list is not complete..i know i skipped some of the rfi
• The black trace is the CW swing, red is the CCW swing
• Where the black and red traces overlay each other in azimuth shows that the rfi is stable in time and coming from a particular azimuth direction (outside of the dome).
• rfi that does not change much with azimuth is probably coming from inside the dome.
  

• To compute rfi pwr vs azimuth i:
• for each 1 sec spec i took the max value within a few channels of the peak value for the az swing.
  
• This list is not complete. I have probably left out some frequencies.
• Page 1: over plot  the 28 rfi frequencies vs azimuth position
• I normalized each frequency to its max value for the swing (to keep them all on the same page)
• I then added a display offset to each spectra (so they wouldn't sit on top of each other
• Each line is then labeled with its frequency.
• Page 2: plot the average power over the azswing for each rfi frequency
• This shows how strong each rfi was
• The actual values are labeled  with
• frequency   Strength(Tsys)
• the strongest rfis were:
• 331.909  3.848*Tsys.. this is a harmonics of little star inside the turret control box
• 315.000  3.063*Tsys.. 
• this is a camera frequency.. the dome cameras were turned off..
• the sb console showed this on 27jan16 with the anritsu, but it did not go on,off during the test on 28jan16..
• 308.000  1.791*Tsys.. also seen with the anritsu 27jan16, but did not cycle during the 28jan16 test..
• We may have a 1 MHz comb coming from something..
  

• Looking through the 140 rfi freq vs azimuth of set 2, i picked 11 frequencies that had a common azimuth dependence
• The two frames over plots these 11 frequencies (6 in the top frame, 5 in the bottom frame)
• I've normalized each frequency to its maximum value for the swing
• the azimuth peaks are at:
• -30deg azimuth .. single peak
• 150 deg azimuth.. multiple peaks
• 330Deg is about the direction of the control room
• This is probably the direct path
  
• 150 is probably rfi scattering into the dome when it is 180 deg away from the control room
• The multiple peaks are probably from the lengths of the platform it is scattering off of.
• Looking back at plot set #2. the 320 Mhz biridie is coming from the computer room air conditioner on top of building 1.
• This has an azimuth peak at 340 deg azimuth..

Summary

• using a higher resolution spectrum (about 1khz) allowed us to see a lot more of the 327 birdies (previously i'd used 6.4Khz)
• hundreds of birdies were seen above the noise floor in  976 hz, 1 second integration (covering 50 MHz).
• Many of the birdies showed no azimuth dependence.. so they are coming from inside the dome
• see sbconsole, turret controller  327 rfi.
• tens of birdies are coming from the direction of the control room

home_~phil