03nov11: possible 2Mhz comb in 327  receiver.

• 327 rcvr centered at 327 Mhz with the 302 to 352 Mhz filter in.
• mock spectrometer with 6.9 Khz resolution was used.
• alfa motor contoller off. dome cameras on.
• a 50 term harmonic was fit to the average spectra and then used to bandpass correct it. 1. was then subtracted.
• PolA and polB were then averaged.
  

• The plots were split up into 10 Mhz sections with .5 Mhz overlap.
• The solid red lines at the bottom of each   plot are spaced every 2 Mhz on the even Mhz.
• The solid green lines are birdies close to 2 Mhz multiples that show an azimuth dependence, measured 09mar11.
• Each of the green flagged birdies has a different azimuth dependence, so they are not coming from the same source.
• They are located at: 306,320,324,330.01,336,340,342,344.07,350 Mhz.
  
• There are still a number of 2 Mhz multiples that have a red flagged birdie present. It is also possible that the green flagged  birdies are hiding a weaker 2 Mhz  birdie that could be part of the comb.

03nov11: alfamotor (top)

• The 327 receiver was centered at 327 MHz with the 302 to 352 Mhz filter installed.
• The mock spectrometer was used with a 57 Mhz bw and 8192 channels (6.9 Khz resolution). Data was dumped at 1 second intervals.
• The on,off sequence for the alfa motor controller was:
• 0 to 65 seconds - motor on
• 65 to 158 seconds - motor off
• 158 to 213 seconds - motor on
• 213 to end   motor off

• The horizontal dashed lines show where the motor was turned off,on,off
  
• PolA entire band (.gif) .
  
• This has been smoothed,decimated  to 43 khz channel resolution.
• 300.538 Mhz: solid rfi from 0 to 65 seconds. Goes away when motor turned off
• 302.85 to 301.62 . Drifting birdie that occurs at 158 seconds when motor turned back on. Disappears when motor turned off.
  
• PolB entire band (.gif) . Smoothed decimated to 64 Khz channel resolution.
• No obvious rfi from motor controller in polB.
  
• PolA  blowup around rfi   with 6.9 Khz resolution.
• You can more clearly see the 300.538 Mhz birdie as well as the drifting birdie when it was turned back on.

SUMMARY:

• Shielding the alfa motor controller has gotten rid of many of the birdies seen back in 02mar11.
• A birdie is still present near 300 Mhz.
• This is probably part of the 10 Mhz comb seen back on 02mar11
• When the controller is turned on a birdie appears at 302.85 Mhz and drifts down toward 300 Mhz.
• Since rfi is still seen from the alfa motor controller it should still be left off during 327 and probably 430 Mhz observations.

02mar11: alfamotor,cameras, distomat rfi  (top)

• 327 rcvr centered at 327 Mhz and the 302 to 352 Mhz filter (this may actually be a straight thru connection).
• mock spectrometer with 57 Mhz bandwidth, 1 second dumps.
• Data was taken for about 400 seconds.During this time the alfa motor controller was turned off, on a few times. The dome cameras were also turned off and then on.

• The image has been bandpass corrected with the median value for the 410 seconds.
• Any constant birdies will not show up.
  
• The horizontal dashed lines show where the devices were turned on and off

• records	action
  80	alfa motor on
  120	alfa motor off
  150	cameras on
  182	cameras off
  210	alfa motor on
  252	camera on
  283	camera off
  302	alfa motor off

• there is a 10 Mhz comb: 300,310,320,330 coming from the alfa motor controller
  
• There is a 7.5 Mhz comb that drifts to lower frequency when the alfa motor controller  turned on.
• the cameras have a comb at 14.3 Mhz spacing
• the 315 Mhz rfi at 200 and 320 seconds
• has pair of rfi spaced by 70 Khz
• spaced in time by 120 seconds
• This is coming from the distomats
  

• Each plot has been normalized by a harmonic fit to the median bandpass during the off.
  
• Constant birdies (in the on and off) will remain).
  
• The vertical scale is tsys units.
  
• Page 1: alfa motor off (black) and alfa motor on (red)
• Top is polA, bottom is polB
• The off has been shifted left by -.05 Mhz so you can see if the on and off's overlay each other.
• Page 2: cameras off (black) and cameras on (red)
• top polA, bottom PolB
• The green lines show the 3 camera birdies at 315.0, 329.30 (weaker), and 343.64

Summary:

• The alfa motor controller is making rfi at 327 Mhz
• There is a 10 MHz comb: 300, 310... 350.
• 320,340 is the strongest
• There is a 7.5 Mhz comb that drifts to lower frequency when the device is powered up
• The dome cameras are making rfi at: 315,329.30,343.64 (343.64 is the strongest) (14.3 Mhz comb)
  
• The distomats are make rfi at 315. Mhz.

11jun09: rfi from sband console, alfa motor (top)

• 327 receiver
• interim correlator with 25 Mhz Bw centered at 320 Mhz with 2048 channels.
• 1 second dumps for 1350 seconds.
• az,za set at :285,11.

• 0 all on
• 155: cameras in dome turned off
• 318: alfa motor turned off
• 421: sband console breaker turned off
• 483: sband console breaker back on
• 1150: sband breaker off
• 1196: cameras back on
• 1277: alfa motor back on.

• It looks like cameras off make a big difference at rec 155, but the rfi did not come back when the cameras were turned on at rec 1187 so it was probably just a coincidence
• at 318 the alfa motor was turned off  and the drifting birdie at 324.5 disappeared. When the motor was turned back on at rec 1277, a 7 Mhz comb appeared at 315. It drifted rapidly.
• 421-483: turning off the sband console breaker got rid of the 750 Khz comb.

• Top: spectral average of records 532-1132 with the sband console on. The vertical scale is tsys units.
• Bottom: blow up of spectral average with sb console on (black) and sb console off (red). The green vertical lines show the location of the sband console comb.
• The 320 Mhz birdie was still there when the console was turned off so it was not coming from the sband console.
• The strongest comb element was 312 Mhz. It had a strength of 4*Tsys in a channel width of 24Khz (after hanning smoothing).

11jun09: after shielding the console:

• az,za set to 190,11.
• mock spectrometer used with a bw of 34 Mhz centered at 327 using 8K channels and .1 second dumps.
• the sband breaker was switched on/off. the record numbers were:
• rec 0: off
• rec 50: on
• rec 102:off
• rec 150: on
• rec 205: off
• rec 254: on
• The data processing averaged to 1 second and decimated the spectra to 1024 take a peak hold within the 8 decimated channels.

• There is no obvious on/off seen when the sband breaker is thrown.. So the shielding must have corrected the problem.

Summary:

• The 750 Khz comb from the sband console was removed after the shielding of the cabinet was upgraded.
• The alfa motor controller is still generating birdies at 327 Mhz.
  

13apr06: testing the trenddata gigabit switch for rfi.  (top)

• The first image (polA) shows the 390 khz band for the 180 seconds (.gif).
• The birdie is at 335.9367 hz. You can see it come and go as we switched the switch on and off.
• The majority of the other birdies are a comb with  a spacing of  39.5 Khz
• The second image is a 50 Khz blowup centered on the birdie (.gif):
• A plot of the 1 second  spectra as well as the total power of the birdie channel (.ps) (.pdf):
• The top frame overplays the 180 1 second spectra (with an offset for plotting). There is a drift of about 1 channel (380 hz) in the spectra. It is probably a thermal shift when the switch is off and then turned back on.
• The bottom frame plots the birdie channel (average of 2 channels about the peak). The black plot is polA while the red plot is polB. The times when the switch was turned on and off are flagged. Pol A is stronger than polB. The strongest is about 11 times Tsys in an 380 hz channel width. Tsys for the 327 receiver is about 120 K.

Conclusions:

• The gigabit switch with no link active  makes rfi through 2 ghz.
• The majority of the rfi is coming from the fiber to copper converter port.
• The strongest rfi is at 476 Mhz. It is 50 db above a 700 K noise floor in 300 Hz resolution bandwidth when a probe is set on the device.
• When the switch is placed in the parking lot next to the control room, a birdie at 335.9367 Mhz can be seen in the 327 receiver. It is 11 times tsys in a 380 Hz channel. It was stronger in polA than in polB. This was the strongest birdie in the 327 Mhz band when looking at the switch in the screened room.

21oct05: 327 Mhz spectral density at output of 1st amplifier (before the rf filter). (top)

• Top: this covers 30 Mhz to 1000 Mhz. The black and red are the single sweeps for polA and polB. The green and blue are the one minute peak holds for polA and polB. The largest birdie in the band is 471.25. This is the video carrier for tv channel 14. The next two largest birdies are 519.25 (tv channel 22) and 187.25 (tv channel 9).
• Bottom: the 30 Mhz to 500 Mhz measurements.

 

03dec03 327 Mhz comb from sband Tx Rack in dome.  (top)

• Fig 1 . A 30 second average with the rack on. The top plot has 24 kHz resolution while the bottom plot has 190 Hz. The vertical units are Tsys.
• Fig 2. The 30 second average with the rack on (black) followed by a 30 second integration when the rack was off (red). The top plot has 24 kHz resolution while the bottom plot has 190 Hz. You can see that turning the rack on created many birdies and it raised the entire continuum level by about 10%.

24nov03 comb at 327 Mhz.  (top)

• Fig 1 Top is the average of the clockwise spin. Black is polA, Red is polB. The units are Tsys (about)...Bottom: This is the average of the counter clockwise spin. The vertical scale is blown up to show the smaller birdies.
• Fig 2 This shows the spacing between the birdies. A baseline was fit to the non-comb values and then removed. All measurements above 1.5 Tsys were flagged as comb members. Combs in adjacent freq channels were collapsed to the channel with the largest value. The frequency difference was then computed between all of the adjacent comb members. The data was plotted with the comb intensity versus the comb frequency step. The points clustered at multiples of 372 Khz with the largest number occurring at 327*2=745 Khz. Black is polA, Red is polB, and green lines are multiples of 372 kHz. The top plot is the clockwise spin, the bottom plot is the counter clockwise spin.
• Fig 3: This is the strength of each comb element vs azimuth position for all of the comb members found. The top plot is the clockwise spin, the bottom plot is the counter clockwise spin. Colors differentiate different comb members (note that the colors on the top plot do not necessarily correspond to the same frequency for that color on the bottom plot).

24jul02 2 MHz comb in 327 Mhz receiver (resolved). (top)

A 2 Mhz comb was found in the 327 Mhz receiver.  It is at the odd Mhz 327,329,331,.. Mhz. It is offset from the Mhz by +3.737Khz. Looking more carefully you can also see a birdie offset by the same amount at 326,328,330,.... The comb must be a 1 Mhz square wave with the even harmonics non-zero because of imperfections in the square wave. The birdie goes away when the receiver is put on load so it is coming in through the front end. The first lo was shifted and the comb remained at the same rf frequency so it is not coming in after the first mixer.
    Data was taken with the correlator in 195Khz/2048 channels (with hanning smoothing). This has a 190 hz resolution.  Band passes were centered at 327,329,331,and 333 Mhz. 1200 records were then taken while various devices were turned on/off and doors opened, closed.
    The 327 MHz birdie was then mixed down close to base band and sampled with the radar interface at 10 Khz. This measured the width and drift rate of the signal.
The plots show the results of these measurements (note.. the plots call it a 2 MHz comb since the odd harmonics were so much stronger):
•  Comb offsets from 327,329,331, and 333 MHz   The comb is offset 3.737 Khz above 327,329,331,333, etc. The spacing is 2 Mhz within the measurement resolution.
• Drift rate of birdie at 327 Mhz.   The for the 157 seconds of the measurement the signal drifted at .041 hz/second. At 327 Mhz this is a stability of .041/327e6= 1.25e-10 fractional change/second. 3.2 seconds of data were taken for each spectra giving a resolution of .3 hz. It has still not been resolved in the last spectra.
• Data was taken for 1200 seconds using the correlator. During this time the doors going out to the stairwell were opened and closed a few times. The doors to the iflo racks were also opened and closed. The plot shows the birdie at 331 Mhz -Tsys  versus time for the 1200 seconds. The only thing that correlates is the opening and closing of the outer doors. Opening and closing the iflo racks did not make a large difference.

Resolution: Conducting gasket in huffman box degrades with time.

01dec03 327 Mhz comb coming from sb Tx room in dome.

• Fig 1 This is the average of the 2200 seconds of data. Black is polA and red is polB (polB has been offset in frequency by a few channels for display). The top plot is the 25 MHz band (24 kHz resolution while the bottom plot is the 195 kHz band (190 Hz resolution). The 190 hz resolution data did not resolve the comb.
• Fig 2. This is the time series for the 321.75 Mhz, 190 Hz wide channel. The top plot is the entire 2200 seconds (it took me awhile to get up to the dome to open/close the doors). The bottom plot is a blowup of 300 seconds when the transmitter room doors were opened/closed twice. The dashed green line is when the transmitter door was opened. The blue line is when the door was closed. (these times could have been off by a few seconds. You can see that the power in the channel went up by almost a factor of 7. This shows that the comb is coming from inside the room.

    The dip at 1250 seconds is when i opened the door rapidly and then closed it to get into the room for the first time. When I closed the door, it must have made better contact than previously.