sband RFI measurements.

last updated 12feb18

30may19: 2380 Mhz rfi from lares tower
12feb18: 100ms period rfi 2389-2398 Mhz
18aug17: 2370-2375 Mhz starts 03may17 ->present
25jan16: 2370-2375 rfi from at&t turned off
19jan16: rfi at 2370-2375 and 2400 mhz during road trip to hq/radio redentor towers.
18jan16: rfi at 2370 and 2400 Mhz from 12 meter site.

02dec15:2397 mhz rfi measured at 12meter coming from yiyi's tower direction.
14sep15: 2380 Mhz Rfi

09aug15: sbn azswings: rfi: 2357-2367 2373-2390,2397-2412
25mar15: 2110-2155 proposed band reject filter
03mar15: How sbw handles the 2110-2155 aws rfi

Rfi at 2394-2403 Mhz

mar12: 2140-2150 Advanced Wireless Service rfi,
01nov11: power shutdown of visitors center.
12oct11: added monthly plots of ism band from hilltop monitoring.
jan11 - rfi at 2380 MHz

    22feb11 - rfi at 2380 goes off when transmitter turned off.
    19jan11 - azswing looking at 2380 rfi.
    12jan11 - rfi appears at 2380 MHz

20sep01 - measuring the power levels at the output of the sbw dewar.

190530 Rfi at 2380 Mhz

    rfi at 2380 Mhz appeared on 28may19 around 11:45  (see hilltop monitoring 190528). It remained constantly on with  a bandwidth around 10 Mhz and 15 db above the 2200Mhz hilltop band noise floor.
The sband radar experiments were affected by this signal.

    How the offender was detected..




170818: 2370-2375 rfi appears 03may17.

    The 2370-2375 Mhz rfi appeared on 03may17.

The hilltop monitor for 03may17 shows when it came on (.ps) (.pdf)

Data was taken through the 305meter using the mock spectrometer on 15aug17. The setup was:

The plots show 30 1 second spectra (.ps) (.pdf):


processing: x101/170815/

25jan16: 2370-2375 mhz rfi turned off

  Rfi at 2370-2375 appeared around 30dec15. This is in the sband transmitter band. The hilltop monitoring showed the approximate time when it  appeared:

  On 19jan16 dana and i went on a road trip looking for the source of the 2370 rfi. We found that it was coming from the  HQ tower above utuado (more info)

    Angel called the HQ tower engineer and complained about it.
Looking at the rfi hilltop monitoring, it looks like the 2370-2375 Mhz birdie was turned off on 25jan16 (.ps)   (.pdf)


processing: x101/160125/

19jan16: 2370, 2400 Mhz rfi during trip to HQ tower.

    On 19jan16 dana and i drove out to the hq/radioRedentor towers  to check the  2400Mhz and 2370-2375Mhz rfi. (we also checked the rfi below 5150 mhz).

    The 2400 Mhz rfi is illegal because it spills below the ism band by about 2mhz.
    The 2370-2375 Mhz rfi  is illegal, and it falls within the 20Mhz band of the sband transmitter.

    We made two stops before arriving at the radio redentor/hq towers:

The 1st plot shows the 2400 Mhz rfi when we looked at yiyi avila's tower from the colmado torres location  (.ps) (.pdf)

The 2nd set of plots shows the 2370-2375 Mhz rfi (.ps) (.pdf)

The 2370-2375 Mhz rfi.

So it looks like sometime between 29dec15 and 30dec15 the 2345-2350 Mhz rfi jumped up to 2370-2375 mhz,.

The 2345-2350 Mhz rfi is band D of the WCS bands.


processing: x101/160119/

18jan16: measuring 2400, 2370 Mhz rfi from the 12 meter

   dana and i went to the 12meter site to check on the 2400 Mhz rfi on 18jan16. The setup was:

The plots show what we saw....
    The plots show the rfi around 2400 Mhz (.ps) (.pdf)
processing: x101/160118/

02dec15: measuring 2400 Mhz rfi from the 12 meter

    dana and i went to the 12meter site to check on the 2400 Mhz rfi. The setup was:
    We looked for the 2380 Mhz rfi, but we could not see it with the setup (probably too weak.. we had  barely seen it fro the platform).
The plots show what we saw....
    The plots show the rfi around 2400 Mhz (.pdf)
processing: x101/151202/

25mar15: 2110-2155 band reject filter

    Dana has been working on getting a quote for an  band reject filter to get rid of the 2110-2155 rfi. It will be placed in front of the current sbw rf filterbank.

    The first  plot has the quote and the wideband band reject  filter performance (.pdf)

    The 2nd set of plots shows a  blowup of the filter response as well as the location of the rfi (.ps)  (.pdf)


processing: x101/150319/

rfi measurements home

03mar15: how sbw handles the 2110-2155 AWS rfi  (top)

    The Advanced  Wireless Services (AWS) transmissions covers 2110 to 2155. This lies with the sbw receiver.
An rf filter bank is available with sbw to filter out some rfi. Its passband filters are:

An or'ing network allows the user to select one or more of these filters.
The 2110-2155 AWS RFI falls inside the passband of filter 2.

The first set of plots shows an average  mock spectrometer covering 2040 to 2200 Mhz (.ps) (.pdf)

Adjusting the sbw power

   The if/lo system has a set of adjustable attenuators and amplifiers to adjust the power levels in the system. There are also two power meters.
The setup is:

There are commands to automatically measure and set the power levels for the upstairs, downstairs, and backend power adjustments.

Auto adjusting the power with AWS in band does not work.

    The auto adjust power algorithm tries to set the minimum power  into the fiber optic transmitter and still have the spectral density high enough so that the fiber optic transmitter does not contribute much to Tsys. The idea is to give the most dynamic range to the system without affecting Tsys.  Unfortunately we need to measure spectral density and we're using a power meter....

    On 24feb15 data was taken with sbw to see how the AWS inband rfi was affecting the system. The setup was:.

3 60 second data sets were taken:
The plots compare the measured system temperatures derived from the 3 sets (.ps) (.pdf)


processing: x101/150224/

mar12: AWS Advance Wireless Service (top)

    Rfi at 2140-2150 Mhz appeared around 10nov11 (in the hilltop monitor system).

So the 2140-2145 is probably T-mobile.
I don't know who is using the 2145-2150

processing: x101/120308

2400 Mhz rfi thru 30apr12

UPDATE: JUN12: This was coming from KS computers using the 2400 ism band for internet wireless communications. They have moved to the 5ghz ism band. 

 Mike nolan reported 2395 rfi on 12oct11 during an sband transmitter run. This is outside the ism band that goes from 2400 to 2500 MHz.:


30apr12:Measuring the 2400 Mhz rfi at yiye avila's tower (roncador).

    On 30apr12, angel and myself drove the rfi van up to yiye avila's tower on mount roncador.

 The setup used to take data was:

The plots show the 2400 Mhz rfi when we pointed at the tower (.ps) (.pdf)
We then drove up to the tower.


processing: x101/120430/

oct11: hilltop monitor data, azimuth swings. (top)

2011 oct hilltop monitor plots (see 08oct11 for the jump)
Spectra taken before and after the jump shows the frequency change of the rfi (.ps) (.pdf):
12oct11 azimuth swing showing position depedence of rfi (.ps) (.pdf)
Dynamic spectra of the azswing:   CW spin .gif   CCW spin .gif


   Mike nolan reported 2395 rfi on 12oct11 during an sband transmitter run. This is outside the ism band that goes from 2400 to 2500 MHz.
    Data from the hilltop monitor system, the telescope data (including an azimuth spin), as well as a helical antenna with the portable spectrum analyzer were used to study the rfi.


Hilltop monitor plots of the ism band:

2400 rfi seen through the telescope.

From the antenna test shack.

    Dana and i took a helical antenna and the portable spectrum analyzer to the antenna test shack. We saw the 2400 MHz  rfi strongest in the direction of roncador (yiyi avila's tower .. or one close to it).

processing: x101/111012/,,

RFI at 2380 MHz. (top)

22feb11 - 2380 rfi goes off when tower transmitter off.

    We made a trip to the radio redentor tower in utuado on 18feb11.
    After talking with the tower owner, an engineer went to the tower and turned off the 2400 MHz user. This occurred around 11:30 AM (we were told after it had happened). At 11:40 ast the rfi had moved from 2380 to 2437 MHz. The engineer at the site agreed that this transmitter was having problems. It would remain off till it was fixed.

    The plots shows the hilltop monitoring before and after the turnoff (.ps) (.pdf)
processing: x101/110222/

19jan11 - azswing looking at rfi

       On 19jan11 azimuth swings were done to look at the 2380 MHz rfi. The setup was:
The plots show the power vs azimuth position (.ps) (.pdf):


12jan11 - rfi appears at 2380 MHz

    17 MHz wide rfi appeared at 2380 in Jan11.  It was first seen in the hilltop monitoring data  on 12jan11.

Hilltop monitoring:

    processing: x101/110119/

20sep01.Measuring the power levels at the output of the sband wide dewar. (top)

    parked at az=309. and the gregorian was at 3.35 degrees.  The measurement was from 1000 MHz to 2950 MHz. The dewar response goes beyond 3 Ghz but the spectrum analyzer didn't want to switch to the next band. The data was taken during close to noon with the sun about 15 degrees away (dec=01 deg).  The plots show: Doing a consistency check on the power levels:
-198 dbm/hz/K + alog10(3MHz rbw)*10 + alog10(40K)*10 + 40 db gain= -77 dbm.
The spectrum analyzer value in the middle of the band where there is no interference is about 17 db higher than this. These measurements need to be redone.

The large interference at 1940 MHz are from cellular phones. The large birdie at 1350 MHz is the san juan airport radar. I don't think that there is any filter between the dewar and the post amps. This needs to be corrected.  We also need to decide what to do about the birdies at 1940 MHz. Do we cut them out with a bandpass filter or try and use a notched filter?  Our spectral line list does not have any lines between 1720 (OH) and 2661 (HC5N).

processing: x101/010920/

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