cband RFI measurements.
last updated 30jul19
cband plane altimeter looks like an frb.
cband 4-5 ghz rfi, azswings done 07feb19.
21jan19: 4250 rfi seen from the 12meter location.
cband azswing covering 4715-5486 Mhz
09aug16: scanning the U-NII
(5.15-5.85) band for out of band emissions
cband azswing covering 4715-5486 Mhz
cband azswing covering 4715-5486 Mhz
redentor tower test: turning off,on cband internet providers
19jan16: road trip to
radioRedentor tower. rfi below 5150 Mhz.
18jan16: 5ghz rfi from the 12meter site.
cband az swing. 5ghz rfi.
02dec15: 5015-5055 rfi looking from 12meter
p2865 cbamd run 4-5 ghz on 13apr14 shows avg and rms spectra
27mar14: 5030-5070, 5070-5100 rfi from
5-6 Ghz on the telescope after rfi turned off.
trip to yiyi's tower. Source of 5020 rfi.
Mhz rfi coming from yiyi avila's tower.
11apr13: 4920 rfi present 06apr13-09apr13.
6900-7050 rfi seen 11mar13,16mar13 by chris salter
azSwings using 6-7 Ghz
azswings 5-6 ghz.
28aug12:5275 xpernet test from jonathan
21mar12: 5990-6020 microwave link interference.
30sep11: 6580-6610Mhz rfi cbandhi
24sep10: 5670 MHz rfi.
21jan19: 4250 Mhz rfi from 12meter
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,
fixed satellite (space to earth)
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
- There also looks to be harmonics or intermods around 4500 and
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
- 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.
- 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
18jan16: rfi below 5150 Mhz from 12 meter
on 18jan16 dana and i went to the 12meter site to
check on the rfi below 5150 Mhz.
The plot shows what we saw
at 5ghz (.ps) (.pdf):
- 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.
02dec15: 5015 - 5055 rfi measured at
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:
When pointing the helix we got a strong signal at
magnetic bearing 155M (this is approximate, i did not use the
compass and the antenna simultaneously). We had thought this was
coming from yiyi's tower.. but his tower has a magnetic angle of 189
deg (from the 12 meter).
- cfr: 5000 Mhz
- span: 198.54876 (200)
- rbw: 1 Mhz
- vbw: .3
- preamp on, avg mode 5 traces, and peak hold
show the strength of the signal (.ps) (.pdf)
- The black trace is an average of 5 sweeps.
- The red trace is a peak hold (probably holding for 30 secs or
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
The U-NII (Unlicensed National Information Infrastructure) band is
used by wifi providers. It covers:
Observers reported rfi between 5030 and
5070 in mar14.
Timeline for rfi:
- ("We" below refers to dana, angel, and myself.)
- 13jan14 5030-5070 rfi appeared:
- 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
- 10:35 am. the 5030-5070 rfi turned off,
- 10:50 we arrived at the tower and didn't see the
- We did see weaker illegal transmissions at 5070-5100.
- This rfi was coming from the del vivi net equipment at the
- 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
- 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
- Middle: 25mar14 data taken on the 305m and the cband
- 1 minute spectra average. i removed a 31 order
- 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
- 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
- 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 -
- 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
- 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
- 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
- 5070-5100 was coming from vivi net equipment on the tower.
This same company had been transmitting at 5020 Mhz back in
- As of 28mar14 these transmissions have stopped.
- there are weaker illegal wifi emissions:
- 5100 to 5150
- We do not yet know if they are coming from yiyi Avila's
- 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
- 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:
the dynamic spectra shows 250
millisecs of spectral data with .154 millisecond resolution (.gif)
- 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.
The plots show the average
spectra as well as total power vs time (.ps) (.pdf)
- 2K spectra were computed (6Khz resolution)
- There are horizontal stripes at 3 millisec spacing.
- a large burst occurs every 102 milliseconds.
The hilltop monitoring plots show when the birdie came and went:
- 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
- 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.
- 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
- Looking at the FCC database, the band allocations are:
- Non government
- 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
28aug12: 5275MHz Expernet test from
Jonathan Friedman's house. (top)
Expernet (xairnet) delivers wireless internet:
Jonathan friedman is installing the service at his house (about 1
mile from ao). We did a test on 28aug12 to see how the service
affects the cband system. The setup was:
Dynamic spectra were made during the transfers for each of the 7
- 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
- PolA and polB have been averaged.
|5475-5485 Mhz has
rfi during 1st 2 transfers
The plots show the strength
of the signal (.ps) (.pdf):
- 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
- 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).
- 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
- 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:
- Page 1: spectral density on/off -1
- These are 300 second on/off -1 spectra taken with cband
- 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
- Black is pola, red is polB
- I've removed the continuum from the source (subtracted
- 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
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
- 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.
- microwave links around 6 ghz look to be about 30 Mhz (from the
- The 5090-6020 rfi is from a microwave link used by the pr
- 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
- Using google maps this line of sight passes close to the
- 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
Rfi was reported in cband high on data taken
30sep11.. It covered 6580 to 6610 Mhz. This rfi had been seen before
back in jun11.
The plots show the rfi from a
300 second "on source" observation (.ps) (.pdf):
Dynamic spectra for 300 seconds
of data (.gif):
- 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
- 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
Source of rfi:
- the rfi has been seen in the hilltop monitoring data since
- It has a bandwidth of 30 Mhz.
- There is a 2nd 30 Mhz band close to 6255 Mhz in the hilltop
- 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
- 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)
- 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
around 5670 (top)
Rfi has appeared at 5670 MHz
the first plot shows the data
in the cband receiver (.ps) (.pdf)
- On the telescope using the cband receiver: 8 MHz about 5670
- 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.
the second plots shows Hilltop
monitoring data with 8 MHz about ieee802.11 channels (.ps) (.pdf)
- black is polA, red is polB. The vertical scale is in units of
- 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
- The 5670 birdie started at 5700 24jun09 then moved to 5670 on
- 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