21jan19: 4250 Mhz rfi from 12meter location.

    The hilltop monitoring system has been showing strong rfi at 4034-4150  and 4217 to 4327 for many years (and chris and tapasi were reporting problems at cband for probably just as long!).
Looking at the fcc allocation page,

The first plot shows the 1 minute peak hold from the hilltop rfi monitor during our measurements (.ps) (.pdf)

• You can see the strong signals at 4050 to 4150 and 4250 to 4350
• There also looks to be harmonics or intermods around 4500 and 4650 Mhz.
  

On 21jan19 felix and I went to the 12meter location to see if we could get a bearing for this rfi.
The setup was:

• anritsu spectrum analyzer
• preamp on
• 2db/division
• no attenuation
• 300 Mhz span centered at 4150
• 1 MHz rbw
  
• trace A: avg 100 sweeps
• trace B: peak hold
• 1-10 ghz antenna
• low loss cable
  
• jgr 1.5 db  nf 20db amp (4-8 ghz)
  
• cable to spectrum analyzer

    We mounted the antenna on a camera tripod and then took measurements at various magnetic bearings.

The plots show the average and peak hold spectra (.ps)  (.pdf)

• Each direction is plotted in a separate color
• the 210 and 233 directions were measured twice (separate by about 20 minutes).
  
• top frame: overplot the 100 sweep average for each direction.
• There is not a very large change in strength with direction.
• The two directions that were done twice do have large differences from the first measurements
• So the signal was changing with time.
• The bottom plot shows the peak hold for each direction.
  

A uls search of licensed operators between 4000 and 4500 Mhz within 50km of AO showed a prtc tower using 4070.

SUMMARY:

• We can see the rfi from the hilltop when using a 20db 1.5db  noise figure amp in front of the anritsu.
• There is no obvious angle dependence with the signal.
• We should probably try to continue the sweep a full 360 degrees to see if we get any angle dependence.
• I wonder if we are getting scattering off of the gregorian dome?
  

18jan16: rfi below 5150 Mhz from 12 meter site

• we used the helical antenna
• the anritsu spectrum analyzer was also used.

• The rbw was 3 Mhz,average 40 sweeps, preamp on
• both signals peaked up when we pointed at 139DegMagnetic. This is the direction of the hq/radiorendor tower.
• We didn't see anything when pointing at yiyi's tower.

processing: x101/160118/rfi12meter.pro

02dec15: 5015 - 5055 rfi measured at 12meter

    Dana and i took the cband helix antenna  and the anritsu up to the 12 meter to look for the 5 ghz rfi that has been seen in the telescope (yet again).
The anritsu setup was:

• cfr: 5000 Mhz
• span: 198.54876 (200)
• rbw: 1 Mhz
• vbw: .3
• preamp on, avg mode 5 traces, and peak hold

• The black trace is an average of 5 sweeps.
• The red trace is a peak hold (probably holding for 30 secs or a minute).

The lat/long table shows some local tower locations and bearings... none match this (although i should probably redo the compass measurement  lining the compass up while i'm pointing the antenna.

27mar14: 5030-5070, 5070-5100 rfi from yiyi's tower

• 5150-5350
• 5470-5825 (more info)
  

Timeline for rfi:

• ("We" below refers to dana, angel, and myself.)
  
• 13jan14 5030-5070 rfi  appeared:
•  You can see the rfi appear in then  hilltop monitoring images .pdf.
• It was on continuously from this date
• 25mar14: from 12meter site we saw that the 5030-5070 rfi was coming from the direction of yiyi Avila's tower.
  
• the 5070-5100 rfi was too weak to get a direction.
  
• 26mar14: angel and i went to the yiyi avila's tower on roncador.
• 10:35 am. the 5030-5070 rfi turned off,
  
• 10:50 we arrived at the tower and didn't see the 5030-5070  rfi
• We did see weaker illegal transmissions at 5070-5100.
• This rfi was coming from the del vivi net equipment at the tower.
  
• This is the same company who was broadcasting at 5020 back in jun13 (more info)
• angel called the company and they moved up to a legal portion of the band. The hilltop monitoring showed it disappear around 12:00
  
• 14:10. back at AO we saw the rfi turn back on
  
• 27mar14:
  
• 10:00 We did a test,monitoring 5030-5070  from the 12meter site while the engineer at roncador turned of his wifi clients one at a time.
• We used our 5ghz helix, an external preamp, and the anritsu spectrum analyzer.
  
• The plots show the rfi ( from the 12meter site) before the engineer turned off the wifi clients (.ps) (.pdf)
  
• Top: data from 12meter site
• black trace: average 5 sweeps, red trace peak hold a few minutes.
• Middle: 25mar14 data taken on the 305m and the cband receiver
• 1 minute spectra average. i removed a 31 order harmonic bandpass.
• On this day the rfi covered 5030 to 5070.
• the 5120 to 5150 rfi is also out of band
• bottom: 25mar14 305m data. rms by channel using the 60 1sec integrations.
  
• When the system for the  4Net  client was turned off, the 5050 rfi went away.
  
• 4Net  is the same client who was illegally  transmitting at 5100 Mhz back in jun13 (more info)
• angel contacted 4Net and told them they were transmitting illegally. They said they would move to a legal frequency.
  
• 15:30: the 4net client moved their signal away from 5050 Mhz
• These images show the hilltop monitoring of the 5-6 Ghz band  26mar14 - 28mar14 (.pdf)
• each page is a separate day. The horizontal axis is freq, the vertical axis is hour of day.
• Data is recorded as a 1 minute peak hold. The 5 Ghz band is sampled once very 20 minutes
• black is high power, white is low power
• Page 1: 26mar14 (angel and phil traveled to yiyi's tower
• the 5050 signal want off at 10:36 (we arrived at the tower at 10:50)
• It was moved up to 5200 and then 5450 (which is an illegal frequency)
• It moved back down to 5060 at 14:10 (it shifted a little in frequency)
• Page 2: 27mar14:
• 10 am: You don't see the signal go away during the turnoff test since the hilltop monitoring was looking at a different frequency band .
  
• 15:30: 5060 rfi moves up to 5450 (an illegal frequency) and then to 5250 Mhz
• Page 3: 28mar14: 5050 Mhz  still clean
  
• You can still see weak illegal emissions at.
• 5100  to 5150
• 5400
• 5440
• 5460

Summary:

• illegal wifi transmission were coming from yiyi avila's tower
• 13jan14: 5030-5070 started
• This came from 4Net.
  
• Back in jun13 this company was also transmitting illegally at 5100 Mhz (more info).
• 5070-5100 was coming from vivi net equipment on the tower. This same company had been transmitting at 5020 Mhz back in jun13
• As of 28mar14 these transmissions have stopped.
  
• there are weaker illegal wifi emissions:
• 5100  to 5150
• 5400
• 5440
• 5460
• We do not yet know if they are coming from yiyi Avila's tower.
• They are probably too weak for the helix and spectrum analyzer at the 12meter site
• We might see something if we move the dome up to 19 deg az=186..
  
• We have seen vivi net and 4net transmitting out of band twice (both times they were out of band for months...). If this continues to happen we need to have a talk with the FCC.

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.