06apr13: 4920 rfi appears for 4 days (top)

    Rfi at 4920 MHz (+/-4,5 MHz) appeared on 06apr13 and remained continuously on  until 09apr13.

On 08apr13 time domain data was taken with the mock spectrometer. The setup was:

• cband receiver centered at 4920 MHz.
• mock spectrometer:
• time domain sampling, 8 bits, polA only, bw=13.2332 MHz
• 20 seconds of data taken
• Telescope: az=280, za=10 degrees.

• 2K spectra were computed (6Khz resolution)
• There are horizontal stripes at 3 millisec spacing.
• a large burst occurs every 102 milliseconds.

• Page 1:
• top: average spectra (for .46 seconds).
• The rfi covers 4915.5 - 4924.5
• Part of the spike at 4920 MHz may be the DC component from the digitizers.
• This looks like the ofdm spectra from the expernet test we did from jonathans house (see below).
• Bottom: Total power vs time for .62 seconds.
• The total power was computed over the 9 MHz of the rfi.
• the time resolution was 154 usecs.
• The large spikes occur every 102 millisecs. these are the wide bursts in the dynamic spectra.
• Page 2:
• top: blowup of total power vs time
• Some of the power spacings are:
• green: .6 milliseconds
• blue:  3.0 milliseconds
• red 102 milliseconds
• Bottom: spectra of total power.
• the entire 20 seconds of total power data was transformed: y=abs(fft(tp)) .. no squaring.
• periods found in the total power data:
• red: 329.8 hz
• green: 337.4hz
• The spikes were spread a bit. The period of the rfi varied a little during the 20 seconds.

• hilltop monitoring dynamic spectra 06apr13-12apr13 (.pdf)
• the rfi started 23 hours (11pm) 06apr13)
• The rfi  remained on until 16:00 on 09apr13
• the data is only samples 1 minute every 20 minutes.
  
• hilltop monitoring daily average spectra 06apr13-12apr13 (.pdf) 
• The rfi got to be about 20 db above the noise floor of the hilltop 4500 MHz band.

Summary:

• rfi  appeared at 4920 MHz on 06apr13 at 23:00. It went away at 16:00 09apr13
• the rfi was 9 MHz wide
• the  average spectra looks like an ofdm spectra
• The power output was periodic with periods of:
• .6 milliseconds, 3 milliseconds, 102 milliseconds.
• the 102 millisecond output was much stronger than the other 2.
• Looking at the FCC database, the band allocations are:
• Government:
• 4800-4940 fixed mobile
• Non government
• No allocation.
• On 08apr13 the cb helical antenna and the anritsu spectrum analyzer was used from the platform to determine the direction of the rfi.
• The rfi is coming from the direction of yiyi avila's tower. It could also be a tower near his.
• Assuming it was not a governmental transmission, the rfi was probably illegal.
  

28aug12: 5275MHz Expernet test from Jonathan Friedman's house. (top)

    Expernet (xairnet) delivers wireless internet:

• It has a transmitter on yiyi Avila's roncador tower.
• It used 10 MHz about 5275 (it may also use other frequencies).

• cband receiver used. 5-6 Ghz monitored.
• Telescope fixed at az=340, za=15 (this is an approximate direction for Jonathan's house.
  
• mock spectrometer, 7 boxes, covering 5-6 ghz. 1 second dumps
• Each box 8192 channels, 172MHz, polA,B recorded.
• We started recording data.
• Jonathan did an uplink transfer, two downlink  transfers, and an uplink transfer.
• Each transfer was about 25 Mbytes.
• During the last uplink transfer, we moved the azimuth from 345 to 320 degs at -.4 deg/sec.

• The horizontal lines show when the transfers occurred.
• sec 134: start uplink
• sec 213: start downlink
• sec 281: start downlink
• sec 525: start uplink.
•  at second 446 the azimuth moved to az=445.
• at second 480 the azimuth starting moving 445 -> at -.4 deg/sec.
• PolA and polB have been averaged.
• 
  

• cfr MHz (.gif files)	low - high freq MHz	Notes
  5075	4990-5160
  5225	5140-5310	includes 5275
  5260	5175-5345	includes 5275
  5375	5290-5460
  5525	5440-5610	5475-5485 Mhz has rfi during 1st 2 transfers
  5675	5590-5760
  5825	5740-5910

  
  

• 5270 -5280 MHz was the frequency used.
• There is also power coming and going at 5475-5485 during the 1st two transfers.
  

• Top: total power (5270-5279.5 MHz) vs time.
• The y axis has been scaled to Tsys.
• The green dashed lines show the start of the xfer.
• The blue dashed lines show the end of each xfer.
• middle: The average spectra for xfer on and xfer off.
• Red: average spectra during the down started at 213 seconds.
• Black: Average spectra 242-263 seconds when no xfer was occurring. 
• Bottom: A blowup of the average on,off spectra.
• The channel spacing is about 160 Khz.
• Part (or all) of the spike in  the middle is coming from the mock spectrometer (DC).

Summary:

• Expernet is transmitting from yiyi Avila's tower (roncador) at 5275 MHz with 10 MHz bw.
• Within the 10 MHz Band, Tsys increases by about 10-30% during a transmission,.
• The downloads are stronger than the uploads.
• The data rates achieved were:
• uploads: .45, .47 Mbytes/sec
• Downloads: 1.1,.56 Mbytes/sec
• The azimuth position for the maximum signal was not used (not sure what is is)
• This is part of the 5.25-5.35GHz U-NII (Unlicensed National Information Infrastructure band).
• 5275 MHz would be channel 54 in the 802.11 (a/h/j,n) standard.
• I'm not sure how this transmitter at Jonathan's house relates to the 4 mile exclusion rule for towers around AO.

21mar12: rfi 5990 - 6020 Mhz rfi (top)

    Chris salter reported rfi at 5990 to 6020 Mhz using the cband receiver. This is getting in the way of a red shifted line of OH??
The plots show an example of the rfi (.ps) (.pdf):

• The data was taken from   file: wapp.20120201.a2334.0001.fits, scans:203200094,95
  
• Page 1: spectral density on/off -1
• These are 300 second on/off -1 spectra taken with cband high.
  
• The vertical scale is Tsys (about 30K). So the on/off max deviation is about .3 K.
  
• The channel width is 48Khz (100Mhz/4096 then hanning smoothed).
• Black is pola, red is polB
• I've removed the continuum from the source (subtracted median).
• Top: this is 5990 - 6020 mhz that chris reported
• 2nd: 6060-6090
  
• 3rd looks like 2.5 Mhz bands
  
• 4th: 6220 - 6250
• Page 2: rms/mean
• the rms/mean for each channel of the 300 1seccond off recs was computed  and then plotted.
• This measures the variability in each channel.
  
• For 48 KHz 1 sec channels this should be
• 1./sqrt(48Khz*1)=.0046

Looking through the rfi database (searching by geographic location and frequency range) i found:

• WQLC960 Puerto Rico state police
• Transmitter at: 18:23:25.0, 66:59:44.0
• highway 446R, isabela. A little north east of san sebastian.
• ASR # 1013172.
• antenna height 9.1 meters
• beamwidth:2.0 deg
  
• Frequency: 6004.5 , 30 Mhz bw,
  
• emission designator: 30MOD7W
• baseband digital rate (kbps):155600.9
• digital modulation type: 128TCM
• Receiver: 18:17:22.1, 66:39:37.3  (radio redentor tower in utuado).
• Quiet zone notification date: 8/28/2009.
  
• quiet zone consent : Yes
• Looking at google maps with the coordinates, it looks like this line of site comes close to the observatory.
• I did not see this signal in the hilltop monitoring system.

Summary:

• microwave links around 6 ghz look to be about 30 Mhz (from the fcc database).
  
• The 5090-6020 rfi is from a microwave link used by the pr police. WQLC960
• It is about .3 kelvin measured in a 300 sec on/off.
  
• The link goes from 18:23:25 (xmiter) to 66:59:44.0 (radio redentor)
• Using google maps this line of sight passes close to the observaory
• The beamwidth of xmiter is 2deg
  
• we visited the radio redentor tower a while back. I remember seeing this microwave link antenna and it looked like it was crossing the observatory.
• This request was ok'ed by the ao quiet zone on 8/28/2009
• There are a number of other 30 Mhz microwave link interferer's  in chris's data.
  

30sep11: rfi 6580-6610 Mhz cband hi  (top)

• top: 300 second peak hold. Red is polA, green is polB. You can see the rfi sticking up between 6580 and 6610.
• When averaging the 300 seconds, the rfi does not stick up very much.
  
• Bottom: rms/mean by channel for the 300 seconds of data. There are large variations in time along each channel.

• The image has been flattened by the median spectra (so the rfi gets divided by its median value.
• You can also see some modulation +/- 35 Mhz from the 6595 Mhz center.

Source of rfi:

• the rfi has been seen in the hilltop monitoring data since 19apr11.
• It has a bandwidth of 30 Mhz.
• There is a 2nd 30 Mhz band close to 6255 Mhz in the hilltop data
• The 6595 Mhz rfi is  a microwave link from mount roncador in utuado (yiyi avila's tower). The fcc uls listing shows:
• WPOR538     AT&T Mobility Puerto Rico Inc.      0003473709  CF  Active  02/01/2021
• 6595 is Roncador to arecibo
• 6256 is also Roncador to arecibo.
  
  
• The plot shows the transmitter location and the directions that it broadcasts (.ps) (.pdf)
• The link that goes from Roncador to arecibo looks like it passes over the observatory.
• The coordinates for the Roncador tower, Arecibo site, and  AO observatory (gps center of az bearing)
  

• location	lat	long
  roncador	18:13:59	66:45:35.0
  Arecibo TCI	18:28:49.8	66:45:36.6
  arecibo observatory	18:20:39.44	66:45:10

  
  
• The longitude for the link is pretty much north, south with the AO only 25 asecs away.
  
• looking at the fcc uls listing for this freq:
• quiet zone notification 5/16/2011, quiet zone consent: Y
• strange that they showed up in in the hilltop monitoring one month before the quiet zone notification.
• Did we have any say in this microwave link passing over AO?
  

24sep10: birdie around 5670 (top)

• On the telescope using the cband receiver: 8 MHz about 5670 (take 18aug10).
  
• In the hilltop monitoring system. here is takes about 20 MHz to come back down to the noise baseline. this system only has 2.5 MHz resolution.
• Rfi appeared at 5700 on 24jun09.
  
• It moved to 5670 on 18sep09 (where it has remained).
• ieee  802.11  (wireless ethernet) has channels close to these frequencies 5680 (20MHz) and 5700 MHz. this may or may not be coming from this.

• black is polA, red is polB. The vertical scale is in units of Tsys.
• Top: 5 second integration +/- 6MHz about 5670.
  
• middle: .1 second average
• bottom: .1 second average   blowup in freq.

• The plots show hilltop monitoring for 2009 thru 2010:23sep10.
• The horizontal axis is days after 01jan09.  24jun10,18sep09, and 01jan10 are flagged width colors.
• The vertical scale is dbm read from the spectrum analyzer on the hilltop monitoring system.
• 8 MHz about each of the frequencies has been averaged.
• the 801.11 channels are 20 MHz wide. On the spectrum analyzer the 5670 birdies looks about 20 MHz baseline to baseline.
• The 5680 is just leaking from the 5670.
  
• the top plot:5670 is not the center of an 802.11 channel. the others are.

summary:

• The 5670 birdie started at 5700 24jun09 then moved to 5670 on 18sep09.
• It has remained present since 18sep09.
• On the telescope it looks about 8 MHz wide.
• On the hilltop monitor system it is about 15db above the noise floor.