Intro

    On 30aug22 azimuth swings at low elevation were done to determine the horizon mask for  geodetic vlbi observations. This page examines any rfi seen during these swings.

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Setup:

• The 12meter was set to xband.
• the setupwcalmap routines was used:
• Standard ifsetup xb
• cfr set to 8646  MHz.
• hardware winking cal used (25 Hz).
  
• 7 mock spectrometer were used:
  
• 172.032 MHz bw polA,B recorded
• cfr: 8219 8363 8505 8647 8789 8931 9073
• 142 MHz spacing
• 512 freq channels
• 2millisecond spectral sampling using 16 bit spectra

• The telescope pattern was:
• az swing at 1 deg/sec between -100 and 282 (and then reversing)
• swings were done at
  
• el=6deg CW
• el=10deg CCW
• el=15deg CW
• The elevation was kept constant at 30 deg
• datataking started at 07:48
  
• each swing took 380 seconds
• we finished at 08:07
• During the observation the sun location was:
• 88 deg az +/-.75 deg
• elevation at start of swing:
• 6 deg swing: sun at 21.5  el
  
• 15 deg swing: sun at 23.75 el
• The tcl command file user/p12m/x101/220839_azswing.tcl was used to take the data.
  

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Processing the data"

• Each azswing was read in with  the idl routine masazswinginp() with the hwc keyword set
• masgethwcal()  was used to  input the file
• input file
• separate out calon,caloff cycles
• average 16ms of each calon, off cycle spectra
  
• return spectra bacalon,bcaloff at 40 ms spacing
  
• only used the calOff spectra.
  
• interpolate the 7 spectra for each 40ms to a single continuous freq band.
• select the data between -90 and 270 degrees azimuth
• interpolate the azimuth position to the center of each .04 second spectra
• the azimuth is recorded once a second.
• add the polA,B  spectra together.
  
• return the spectra in increasing azimuth (so the 3 swings can be easily  over plotted).
• generate a dynamic spectra for each azswing.
• each data set had  9000 spectra of 3066 freq channels(after interpolating the 7 spectra.
  
• 360/.04sec=9000
• channels by 3000 spectra.
• these were averaged to generate an image that could be displayed
• average by 2 in freq and 12 in time ending up with a  1533  channels by 750 spectra
  
• 336 Khz freq resolution, .8 sec time resolution (or .48 deg  in az since we moved at 1 deg/sec)
• The spectra were bandpass corrected by dividing by the median spectra.
• continuum spectra were not removed (normally by dividing by the total power in an rfi freq region).
  
• Each dynamic spectra was displayed with low and high sensitivity (to see the location of the strong, weak rfi.
• The rms/mean by frequency channel was computed for each az swing (9000 spectra)
  
• larger rms/mean values show channels with rfi.
• The frequency channel with rfi were located and the then total power was computed within this freq range for each spectra.
• The rfi total power was then plotted vs azimuth.
• If the rfi repeated at the same azimuth for the 3 az swings, then this is probably the direction for the rfi.

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Looking at the data:

 Dynamic spectra

  The table below contains the dynamic spectra for the 3 azimuth. For each swing a high and low sensitivity image is made.

azSwing	elevation	HighSensitivty	low sensitivity
1 (CW)	6	.png	.png
2 (CCW)	10	.png	.png
3 (CW)	15	.png	.png

• The continuum power was not removed.
• it was strongest at the lowest elevation.
• this is the beam seeing ground objects. As you move higher in elevation, they are on longer in the beam.
  

peak hold spectra, azimuth of rfi

  
 the plot shows the PeakHold spectra and rfi vs azimuth position (.ps) (.pdf)

• Page 1: peak hold spectra for each azimuth swing
• each color is a different azimuth swing
  
• the continuum power has been removed
• the 8200 MHz rfi appeared in the 6 and 10 deg el swings
• the 1st swing had the rfi suppressed since it occurred during the continuum power.
• the 8340 was present in all 3 swings. It was strongest in the 6 deg elevation swing.
• Page 2: rfi power vs azimuth position
• top: 8179-8245 MHz rfi
• It was strongest in the second azimuth swing.
• it jumped in azimuth between the 2 azimuth swings.
• it is probably time variable.
• bottom:
• 8319 to 8348 rfi
• strongest in 6 deg elevation swing
• centered at az=140 in all swings
• the rfi appears again +/-70 deg from 140 deg.

SUMMARY:

    the following rfi was  seen at low elevations azimuth swings.

• freq	seen in 12aug22 swings	in elevation azswings	strength (Tsys)	az position
  8194.6  to 8267	yes	not seen
  8166.5 to 8274.1	yes	el=10 only	> 2	az=263.4 not seen in el=6,15
  8318.9 to 8348.7	yes	el=6,10,15	> 6	az=140 with smaller spikes +/- 70  deg from center stronger at el=6
  8715 to 9005	no	el=6,10,15	>3	seen in all az, elevation. strongest peak at el=10,az=-19 4 sec periodicity. 12 20MHz bands with guard bands. saturates the receiver system.

  
  

processing: x101/220822/xbazswing.pro