21mar12: rfi 5990 - 6020 Mhz rfi

    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: 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 probably 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
• The plot shows the transmitter location and the directions that it broadcasts (.ps) (.pdf)
• The link that goes from the transmitter to arecibo looks like it passes over the observatory.
  

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.