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
combs
look for ionosonde transmissions in 327 receiver,.,
Summary
Previous 327 azswings:

• 25jan16 327 az swings
• 09mar11 327 azswings
  

Introduction (top)

The setup:

• 327 MHz receiver. 750MHz narrow band IF
• azswings 270 to 630 degs and back at .4 degs/sec (probably should do it at .35 deg/sec next time). Dome at za=18 deg.
  
• 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)
• .1 sec sampling
  
• The alfa motor controller was turned off during the azimuth swing
• The dome cameras were turned off toward the end of the 1st (cw) azswing.

Processing the data: (top)

• For each azimuth swing a bandpass was constructed from the 993 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 993 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 993 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)

• The horizontal green dashed line in the CW spin is when the dome cameras were turned off.
• You can see the birdies go away at:306.x,315.x,321.x,329.x,335.x,343.x,
  
• 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 birdies have no azimuth dependence. This tell us that they are probably coming from inside the gregorian dome.

Plots of the rfi

Average and peak hold spectra:

• 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 993 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.

Azimuth dependence of individual rfi frequencies.

• I went through and selected 143 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.
  

Rfi with no az dependence (from azArm, or 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 9 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:
• 329.314   18.6*Tsys .. dome camera (only in cw spin)
• 321.124      4.3*Tstys.. dome camera (only in cw spin)
  
• 331.909        .25*Tsys.. this is a harmonics of little star inside the turret control box
•  
  

Rfi with common azimuth directions.

• peaks within az 125-165  and peaks 180 deg below. (.ps) (.pdf)
• there are two azimuth peaks. separated by 180 degrees.
  
• peaks within az -90 to 10 deg with no peaks 125-160 (.ps) (.pdf)
• these only have a peak at the -90 to 10 deg range.
• the 320MHz birdie at -40 degs comes from the AC unit atop building 1.
  

Combs seen in the 327 band:

• The average spectra for the cw and ccw spins were plotted in 4 frames (12.5 MHz/frame).
• black is the clockwise spin, red is the ccw spin,
• Page 1: 1MHz comb
• the blue vertical lines are placed every 1 MHz.
• An rfi birdie is seen at each 1MHz.
• a 2 and 1MHz comb was seen back on 24jul02 coming from the 430tx power meter in the dome. Check to see if this is really powered off (more info)
• Page 2: 1 MHz comb
  
• top shift each  comb element to DC and then overplot (with a display offset).
• The comb stays aligned with 1 MHz comb spacing.
• Some of the elements have other rfi on top of the 1MHz element.
• bottom: plot peak value for each comb  element.
• 325 MHz  is the strongest element (.3*Tsys)
• 328 MHz is the 2nd strongest
• 307,and 320 are larger, but they have other rfi in the freq bin.
  
• page 3: comb  from encoders
• same plots as page 1 except that blue flags are now at the encoder comb
• comb =.8192MHz . used 323.581 as one of the comb positions. 
• Page 4:  verify that  .8192MHz is the correct comb spacing.
• Use 323.581 MHz as the comb  reference freq
• Shift each comb element down to DC.
  
• Top: use .8189 MHz as the comb spacing. the birdies move to higher frequency
• Center: use  .8192 MHz as the comb spacing.. things remain aligned.
• Bottom: use .8195 MHz as the  comb spacing. birdies drift to the left.
  

ionosonde transmitting (top)

• use a 7 baud barker code of 20usec baud (140 usec rf pulse)
• use a 25 ms ipp.
• output 8 ipps at one frequency, then step to the next frequency
• go from 1 Mhz to 20Mhz
• steps start around 10Khz and go to 200 Khz at the top end
• the transmision is then
• 140 usec rf pulse every 25 ms 8 times at 1 freq:  total 200ms
• step in frequency every 200 ms
• total transmission time 60 secs + any slop when changing frequencies.

• 16:00 ionosonde started transmitting
• azimuth was 35.1 deg
  
• 16:02 ionosonde probably done
• azimuth was 83 deg
• so the azimuth swung through the direction of ionosonde during the transmission.

    How fast was the ionosonde frequency stepping at 325 MHz? If via harmonics

• tx = 1 MHz, step .01 Mhz, harmonic = 325, freqStep at 325Mhz = 3.25 Mhz.
  
• Steps every .2 secs
• In 1 sec it would step 16.25 Mhz
• tx=20 Mhz, step .2 Mhz, harmonic=16.25, freqStep at 325 = 3.25 Mhz
• steps every .2 secs
• in 1 sec it would step 16.25 Mhz

• All 7 freq bands were combined.
• The data was smoothed and then decimated to 30  Khz (from .9khz).
• The y axis was smoothed by 4 to fit on the screen. This gave a time resolution of .2*4 - .8 sec.

Looking at 10 seconds after 16:00 there seems to be something from 309 to 322 Mhz, but the spacing is less than a Mhz.
To Get a better idea whether the ionosonde causes trouble in the dome receivers, we should probably dump data fast, and look for the 140 usec rf pulse repeating itself at the 25 ms ipp.

processing: x101/190110/azswing327/ionosonde.pro

Summary (top)

•  The average and peak hold spectra were plotted
• Over 143 frequency  birdies had Levels greater than .2 Tsys
• 9 frequencies had no azimuth dependence. Most of these came from the cameras in the dome.
• There are two sets of rfi that have:
• birdies with az 126-165 deg and a peak 180 deg below that.
• birdies with peaks in -90 to 10 deg with no birdie at + 180 deg.
  
• The table lists the source of some of the known birdies:

• Source	freq MHz
  dome cameras	300.675 314.996 321.3145 329.314 strongest 335.629 343.629
  1MHz comb	325,328 MHz strongest
  encoder comb	.8192MHz  spacing includes 323.581
  little star	339.909 little start clock harmonic
  fmStations	308.7 = 102.9*3   HQ 312.3 =  104.1*3 radio redentor 319.5 = 106.5*3 321.9 = 107.3*3
  ac 80MHz harmonic	320= 80*4

• No obvious signal was seen from the ionosonde in the 327 band
• But we probably need to redo the experiment sittting still with fast sampling.
  
• Things to do
• the 329.314 Mhz dome camera birdie is 20*Tsys in a 1Khz rbw. We need to check whether this is coming from a camera, the multiplexor, or a bad cable.
• Find the 1 Mhz comb. It may not be the the 430tx power meter since this comb is on top of 1 Mhz to better then 450 Hz. The 430tx pwr meter was offset by about 3 khz (and drifted).
  
• We need to do a better job with the encoder birdies. Could we have a damaged encoder cable running from the encoder to the vertex shelter?
  

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