430 band RFI measurements.

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01/06dec06 large birdies near 419Mhz saturate receiver

06dec06: large birdie at 419.2 Mhz

    The birdie was seen intermittantly between 12:30 and 14:30 AST on 06dec06. The telescope was sitting at az=312.2, za=10. This was the only time it was seen. It was not seen during a few hours of monitoring on 01dec06 or 30nov06. It was also not seen in any of the x111 data taken during nov06,dec06 (about 11 1 minute integrations spread over midnite to 10am).
    The plots show the characteristics of the 419.2 Mhz Birdie (.ps) (.pdf):

• Page 1 Top 5 minute averages:  30 5 minute spectral averages are overplotted.  Black is polA, red is polB (the feed is circular). The birdie was not resolved in the 24 Khz channel widths (after hanning smoothing). The amplitude of the birdie averaged over 5 minutes got up to about 12000 times Tsys. Since the birdie was not on all the time, the actual strength was greater (see below).
• Page 1 Bottom the strength of the birdie  channel. The strength of the single birdie channel (averaged over 5 minutes) is plotted. It reached a peak during the 5 minute average at 14.36 (14:21 ast).
• Page 2 top birdie channel strength 1 sec resolution: This plots the 24 Khz channel at 419.2 Mhz vs time with 1 second resolution. The vertical scale is now db's above Tsys. The  constant value of 50 db probably means that the system was saturated. The slow rise of Tsys around the green dashed line is the galaxy passing through the beam.
• Page 2 bottom how long did the birdie stay on. This plot shows how long the birdie stayed on (within the 1 second integration). The most common duration was 3 seconds. At 14.3 hours it stayed on for 25 seconds at a time.

01dec06: large birdie at 418.625 Mhz.

    The 418.625 Mhz birdie was seen for about 1 hour between 11:30 and 12:30 AST on 01dec06 (after this time the frequency was changed so we have no data). 1 second spectra were taken as well has baseband data with 100 Khz bandwidth. The 1 second spectra have 48 Khz resolution (after hanning smoothing).
    The plots show the 418.625 Mhz birdie in the 1 second averaged spectra (.ps) (.pdf):

• Top a 1 second spectra. Black in polA and red is polB. The dashed green line is at 418.625 Mhz. The birdie has not been resolved in the 48 Khz channel. For some reason polA is  a lot stronger than polB (even though the main beam of the feed is circular).
• Middle the time variation of the birdie. This shows the 48 Khz channel at 418.625 Mhz vs time (with 1 second resolution). The birdie gets up to about 7000 times Tsys.
• Bottom how long the birdie stayed on. This shows how long the birdie stayed on vs time. The most common duration was 3 seconds.

    Baseband data with 100 Khz bandwidth was taken after the 1 second data above. The spectra were computed using 100 Hz resolution (1K transforms). This gave a new spectra every 10 millseconds.
    The image shows the dynamic spectra of 10 seconds worth of data (.gif):

• The birdie turned on twice in the 10 seconds. The ghost at 418.75 is probably instrumental. The birdie has a carrier and then a modulation phase. Some of the properties are:
• The birdie is on for 2.07 seconds.
• The modulation is on for .53 seconds
• The birdies are spaced by 5.55 seconds. This is a little different than the 1 second data.
• It does not look like this system was going into saturation during this time. The data was taken through the radar interface with a 12 bit a/d converter (the 1 second averaged data used the 9 level correlator).

    The final plot shows the birdie spectra averaged over a single pulse when the modulation was on and when it was off (.ps) (.pdf):

• The black trace is averaged over 50 milliseconds when the  modulation was on. The red trace was averaged over 67 milliseconds when the modulation was off. The vertical scale is db's above Tsys. It got up to about 50 Db (being on during the entire time).  It is about 2.4 Khz when the modulation is off and 9 Khz when the modulation is on. This data was probably not saturated.

Summary:

• A birdie at 419.2 Mhz was seen on 06dec06.
• The birdie was not resolved with a 24 Khz channel width.
• Within a 1 second  spectra the strength got up to 50 db  above Tsys ( in a 24 Khz channel width).
• The receiver system (using the interim correlator saturated during the birdie).

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04oct06 - az,za encoder 614 Khz comb seen at 430Mhz   (top)

• Top: average of 1 strip (135 1 second samples). Black is the new encoder (05oct06 am) and red is the old encoder (06oct06 am). The green vertical lines are at the comb frequency (computed from the 327 Mhz data).
• Middle:  A vertical blowup of the top plot. The red old encoder has been offset vertically to compare the two days. Most of the small spike (at the comb frequency) are gone on 06oct06.
• Bottom: Blowup of the 432.539 Mhz comb element. This was the strongest 430 Comb element seen in the lab (with the new encoder). The birdie at 432.539 decreased, but so did the birdie at 432.575 Mhz. These are probably some other birdies (not coming from the encoders).

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06dec05 Ac units in dome cause birdies at 430Mhz   (top)

• A dynamic spectra of the 1000 seconds of data  shows the birdies. The Old Ac was turned off around 360 seconds and turned back on at 748 seconds. The dashed horizontal lines bracket when the old Ac was off. You can see the rfi that stopped when the old AC was off. The strongest are spaced 2 Mhz apart (missing the even harmonics).
• Median spectra when the AC was on and Off (.ps)  (.pdf): The median spectra was computed for when the Ac was off (black lines) and when the Ac was on (red lines). The green lines are spaced every 1 Mhz anchored at 418.52 Mhz. The vertical scale is in units of Tsys (about 60K). The Ac off spectra is offset by -.002 Tsys for display purposes. The strongest birdies are at 418.5 and 424.53 Mhz.

 

02dec05: birdies at 430 Mhz with 1 minute periods.  (top)

• 25 Mhz bw, 2048 channels, 1 sec dumps, cfr of 430.
• Data was taken for about 2 hours while sitting at az=270, za=10.

• Dynamic spectra for 300 seconds, polA (.gif): This image is spectral density (time vs freq). The small dots are the time variable rfi. The short lines at the bottom of the plot are added to show where these birdies occur (some of the weaker periodic birdies were not flagged).
• Time and frequency extent of birdies (.ps) (.pdf): The top plot shows the power in the 429.89 Mhz birdie vs time. It lasts for 3 samples so the time duration of the signal is about 2 seconds. The bottom plot shows a spectral blowup of this same birdie. The freq. resolution (after hanning smoothing) is 24 Khz. The fwhm is about 3.5 channels so the birdie is about 30 khz wide.
• Time periodicity of channels over 1500 seconds (.gif): The spectra from the first 1500 seconds of data was interpolated in time and then  fft'd along the time direction. The image shows periodicity vs Rf frequency. The vertical scale is in milliHz. The horizontal dashed lines are plotted ever 16.66 milliHz (1/60.  seconds). You can see strong periodic combs around 422-423 Mhz, 430 Mhz, and 432.5 Mhz. These channels have birdies that have a 1 minute period. There are also some channels that have a weaker 1 minute periodicity (but do not show up well in this image).
• Birdie power vs time for 140 minutes (.ps)   (.pdf): Thirteen freq. channels with 1 minute periodicity were selected. The power in the channels were averaged over 7 freq. channels and then plotted versus time:
• Fig 1: all 140 minutes. Each color is a different birdie. The top plot is polA while the bottom plot is polB. This data taking session started at about 9 am. You can see that the birdies were stronger at the beginning of the run. Looking at the data toward the end of the run, the periodic birdies were still seen at some of the frequencies. The gaps in the data are where no data was taken (between scans).
• Fig 2: This is a blowup in time of fig 1 showing the first 5 minutes of data. The dotted lines in polA (top) show how the birdies are aligned in time. You can see two groups. The first starts at 422.72 (lower black trace) while the second group starts at 429.89 (light blue middle trace). The nth birdie of each group occurs at the same time.
• Fig 3: (power in periodicity) vs period:  For each birdie, 8500 seconds of data was interpolated and then fft'd. The plot shows the power vs periodicity. There is a comb with 16.6 millihz spacing (1/60 seconds). The width of the comb was 1 channel (about .1 millihz) so the 60 second period is relatively stable.

 
Summary of birdies:
 
 

period	1 minute
freq. width	about 30 Khz
time Duration	about 2 seconds
birdie groups	4 birdies per group rf spacing: .45,.1 .1 .1 Mhz tm spacing in group: 13,7,26 seconds each group repeats every 60 seconds.
group rf  spacing	7.2 Mhz between groups.
birdie freq.  (strongest)	422.72, 423.18, 423.25, 423.35 grp1 429.89, 430.31, 430.39, 430.48 grp2 432.67
when appeared	looking at the x111 data for oct/nov05 we had: 18oct05 : 2 scans worth of birdies 26nov05: birdies started to appear more regularly


    On 30nov05 A2125 also saw a group of birdies at 432 Mhz. The 7.2 Mhz spacing looks close to the comb that is generated by the alfa motor controller.  The 1 minute birdies are also seen at 327 Mhz (see 327 dynamic spectra of 3rd az swing). The dots around 318.6 are spaced by 1 minute (20 deg azimuth = 1 minute in the plots).These were done with the alfa motor controller turned of.
 

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08oct03: Filter in front of 430 dewar removes tv station intermods.

processing: x101/Y04/051008/430.pro

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30jul03 Insert 422 to 442 filter after the dewar.

19jun03 430 birides vs az, Tv station intermods.  (top)

• chn 14 F1Video=471.25 F1Audio=475.7
• chn 22 F2Video=519.25 F2Audio=523.75

 

 

chan 14,22 intermods in 430 band

combination	freq
2*F1Video - F2Audio	418.75
2*F1Video - F2Video	423.50
2*F1Audio - F2Audio	427.75
2*F1Audio - F2Video	432.25

We see the birdies at 427.75 and 432.25 clearly in the data. It turns out that the 435.75 Mhz birdie is the 432.5 biridies aliased back into the band.
    The correlator was setup for 12.5 Mhz bandwidth centered at 430 Mhz. The edges of the band are at 430 -/+6.25Mhz = 423.75 and 436.25 Mhz. The 423.25 intermod is .5 Mhz below the bottom of the band. The digital filtering in the correlator is done on the complex i,q paths separately. This causes aliases on one side of the band to appear on the opposite. A birdie at .5 Mhz below the bottom of the band will alias into .5 Mhz below the top of the band. So 423.25 will show up at (436.25-.5= 435.75Mhz). We see this birdie in the correlator data.
    Azimuth swings were done to measure the directionality of the birdies. The dome was set at 19 deg za and the azimuth was swung from -90 to +270 degrees and then back to -70 deg moving at .4 degrees per second. The correlator was setup to dump 1024 channels over 12.5 Mhz once a second with the center freq set to 430 Mhz. The input data was then hanning smoothed.
    The average of each spin was computed and then a fit was made to the bandpass using harmonic functions up to order 10*az and a 3rd degree polynomial in az. Outliers were excluded from the fit (see corautobl()). Each 1 second integration was bandpass corrected by dividing by this fit and then subtracting 1 (so the units are Tsys).  The channel containing the peak of each birdie was plotted versus azimuth. None of the birdies drifted in frequency.

The first plot shows the average and peak spectra for the first az swing.

• Top: this is the average of the entire swing.
• middle: The peak value in each channel for the entire swing is plotted. The spike at 427.75 continues up to 975.
• bottom: a blowup of the peak spectra.

• 426.25 Mhz birdie. This peaks at 300 degs az. It is not the tv station.
• 427.75 Mhz birdie. Tv intermod 2*F1Audio-F2Audio
• 432.0 Mhz birdie.    No az dependance. It must be inside the dome.
• 425,426.84, 432.25, 435.26, 435.75 Mhz birdies.
• 432.25 is 2F1Audo-F2Video.
• 435.75 is the 423.5 birdie aliased to the other side of the 12.5 Mhz filter.
• 426.84, 435.26 may be from other parts of the tv signal (color,etc..).
• 425 Mhz may not be from the tv station. It does not have the strong spike in polA at az=124 degrees.
• PolA lines up with az =124 for all the signals.
• PolB is a bit more scatterd.
• The 430 dome main beam is circularly polarized. These signal are coming in the sidelobes and the polarization properties are probably different. Since there are two separate transmitters at two different locations creating these intermods, it may be that the two polarizations are sensitive to different transmitters.

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More on the 426.25 Mhz birdie (doppler shift birdie via the azimuth spin) (top)

• Top: The cross spectra (fft(chVolt*grVolt) image shows +/- 5 hz on the horizontal axis and -90 to 270 azimuth position on the vertical axis. You can see a sine wave in the data with an amplitude close to .5 Hz. The minimum is close to az=120 degrees. This puts the zero doppler at az=30. This should be the location where the azimuth arm is pointing at the transmitter (doppler=0). The amplitude peak of the spectra was at -60 degrees. This is 90 degrees away from the birdie direction. It should also be noted that -60 degrees lines the azimuth arm perpendicular to the T12,T8 side of the triangle.
• Center: This shows the spectral density (+/- 200 hz) of the dome signal on the horizontal scale and time on the y axis. You can see the signal chirp from 35 hz up to 110 hz and then back down in about 5 seconds. The pattern repeats every 12 seconds. This sweep looks like a phase locked loop that has become unlocked (see 100 Mhz reference comes unlock).
• Bottom. This is the same image as the center plot with the vertical scale changed to azimuth direction. You can see the strong signal at an azimuth of 300 degrees.

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23oct02 410 Mhz birdies.     (top)

1. Fig 1 frequency  of the birdies. 101 second averages with dome at 18 deg za and az at 270 deg.
2. Fig 2 time variation of the 410.5249 birdie. 101 seconds with telescope stationary.  Red is polB, black is polA. The adjacent channels are plotted in blue and green (blown up by 300 and 100). The birdies are varying by up to 100 % during these 100 seconds.
3. Fig 3  PolA azimuth variation of the signals. 4 Azimuth swings were done with the dome at 18 degrees za and the azimuth moving at .4 degs/second. The data was sampled once a second.
4. Fig 4  PolB azimuth variation of the signals. 4 Azimuth swings were done with the dome at 18 degrees za and the azimuth moving at .4 degs/second. The data was sampled once a second.

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23apr01 430 dome. Multimeter, power meter inside new rfi enclosure. (top)

1.   45 records: cabinet back door open, rfi box open, meters on.
2.   30 records: cabinet back door closed, rfi box open, meters on.
3.   60 records: cabinet back door closed, rfi box closed, meters on.
4.   60 records: cabinet back door closed, rfi box closed, meters off.
5. 120 records: cabinet back door closed, rfi box closed, meters on.
6.   60 records: cabinet back door closed, rfi box closed, meters off.

1. The first image shows the 195 Khz band with horizontal stripes where the changes were made. The birdie at 433.325 is from the power meter. It completely disappears only when the meters are turned off (4th section from the bottom). The birdie at 433.351 also goes off when the meters are turned off.
2. The second image is a blowup in frequency of the first. You can see that the 433.325 birdie is still visible in the 3rd section from the bottom where everything is closed up and the meters are on.
3. The plots show the power in the 433.325 Mhz channel versus time. The data was normalized to the average value for the 30 records when the back door was open (maximum signal), divided by the average of 10 adjacent channels (to remove sky variation), and then converted to db. It contains the power from the birdie + Tsys (about 60K). Closing the back door of the cabinet reduced the power by 18 db. Closing the rfi box reduced it another 10 db. The bottom plot shows there is about .1 to .4 db leakage with the rfi box all closed up. Averaging the spectra in the 3rd section gave a birdie of about 2 Kelvins.

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11apr01 430 dome. Multimeter inside new rfi enclosure.     (top)

An rfi enclosure for the multi meters, power meter was placed inside the right cabinet on the turret floor.  The multi meter used to read the receiver temperatures was put in the box and hooked up to the gpib bus. The correlator was setup for 195 Khz by 2048 channels (95 hz channel width). Integrations were done with the rfi box open  and closed (both times inside the right cabinet). An integration was also done with the second multi meter in the left cabinet on  to show the reference birdie. A linear baseline was fit to the interference free part of the spectra and then used to normalize the averages to Tsys. 60 deg Kelvin was used to convert from fractions of Tsys to Kelvins.
The plot shows:
• black - 1400 second integration with the multi meter in the rfi box. No birdie is seen.
• red     - 100 second integration with the 2nd multi meter on in the left cabinet to show the birdie at 429.73993.
• blue    - 400 second integration with the front  panel to the rfi box open. No birdie is seen.
• dark red - the baseline used to normalize the spectra.

It is interesting that we see no birdie from the multi meter in the right rack even when the front to the rfi box is open.
processing: x101/010411/multimeter.pro

22jan01 Using the dome 430 Mhz system to look at the vittara jeep parked by the control room. (top)

The vittara jeeps are not shielded and are often used in the parking lot next to the control room. We tried to see if any rfi from the jeeps was getting into the 430 dome receiver system. The dome was as az=350deg and za=19deg. The jeep was as close to the control room as possible looking toward the dome. The jeep was turned on at the minute and turned off at the minute + 30 seconds. This was repeated for 7 minutes. The correlator was set for 12.5Mhz bw, 1024 channels and readout at 1 second intervals. Images were made of the spectral density function (frequency versus time).  (The images below are about 800Kb ps files). The solid lines in the images are the start of a minute (jeep on) and the dash lines are the 30 seconds (jeep off). (some of these lines were lost in the conversion from postscript back to the screen).
• Figure 1 has the band pass normalized to the median band pass for the 420 seconds, 1 subtracted, and then clipped to +/- .02 Tsys. There is rfi and continuum sources but nothing obvious from the jeep.
• Figure 2 is also flatten by frequency channels 400 through 500. This gets rid of the continuum sources (as well as any continuum from the jeep). There does not appear to be any frequency dependent spikes correlated with the jeep going on/off.

Looking at the total power versus time also does not show any obvious correlation with the jeep. We need to redo the experiment with the jeep in the beam (maybe at the fork before you get to the rim road).
processing: x101/010122/vittara.pro