lband RFI measurements.

last updated 13jan16


23jun20: aerostat compression, spikes all across puppi band.
24apr20: check aerostat blanking


05mar19: high time resolution power levels in lbw (checking the radar power)
22feb19 rfi power levels in lbw receiver.


04apr18: GPS L3 signal remains on for 3+ hours.
21mar18: p3058 puppi saturation from lband radars.


19oct16: p3094 on/offs lbw. gns rfi.
18aug16: gps L3 rfi in a2048 data for month of jul 2016.
20may16:p3094  puppi data sees gps satellite
13jan16: a2981 on 03jan16 saw 66Khz comb at 1667.5621 Mhz


06oct15: 1670-1675 rfi on/off transmitter tests with lightsquared.
11sep15: 08jul15 wapp data taken with 1670-1675 rfi present
02sep15: The 1670-1675 Mhz rfi
23jun15: added p2030 zaplists through 23jun15
21apr15: hilltop monitor image of lband radars


11aug14: p2030 pulsar search zaplists and periodicities created by puerto rican radars
08aug14: punta salinas not using modeA starting jul14
05aug14: added monthly plots of 1325 mhzband from the hilltop monitor system.


12dec13: punta salinas blanking sector changes from 78 degrees to 22 degrees in around jun12
29nov13: fraction of time gps l3 was seen in A2811,A2754 data during nov13
26nov13: check the duration of the punta salinas blanking (in the AO direction).
04oct13: punta borinquen radar blanking re-enabled.
29may13: 1419.963,1667.957 birdies from dustbin controller on az arm
09may13: narrow band tone at 1200 Mhz.
29apr13   measuring the punta Borinquen radar blanking in the AO direction.
23apr13  punta Borinquen carsr 1274,1332 Mhz radar
14feb13: galfacts see broadband rfi in alfa
01feb13: x111 dynamic spectra for lband nov/dec12


01jul12  glitches in rf from alfa monitoring are only present with bias monitoring.
17may12: galfacts see galileo rfi at 1278.7 Mhz


02nov11: puntasalinas creates intermods in alfa
01nov11: power shutdown of visitors center.
29sep11: 1408 Mhz rfi coming from the AC unit atop building I.
26sep11: 1408 Mhz rfi in alfa  data.
16aug11: 1360 rfi azswing
15aug11: 1360 narrow band rfi
03jun11:  A2335 polB compresses with longer recovery time.
28mar11: radar intermods in galfa spectrometer.
14mar11- 1357.2 Mhz rfi.


01oct10: 1340 Mhz tone after replacing radar blanker gasket.
28sep10: 1340 Mhz tone coming from radar blanker lo.
27sep10: freq scan of lbw. dynamic spectra, avg spc, rms/mean, tp vs time.
27sep10: gps l3 in a2010 data. on for 26 minutes


08nov09: 1375 mhz rfi.
11sep09: 1390 rfi  in alfa coming from aerostat
16may09: intermods seen in alfa/pdev
16may09: table of mixer intermods for alfa/pdev
05may09: rfi from lbw crosshead.
26apr09: radar looking rfi in alfa data at 1403,1424, 1475 Mhz.
11apr09: gps l3  in a2010 data jan09-mar09
20mar09: 1422.5 MHz birdie from tv channel 54.
19mar09: GPS L2, GLONASS L2, and COMPASS E6 rfi 1200-1300 MHz
13mar09: 1384, 1424 birdies seen in alfa.
23feb09: 1385 Mhz birdie in alfa from aerostat.


23sep08: baseband data take during gps L3 test.


03apr07: radar comb seen 28mar07 in serendip 5 using alfa.
13feb07: some rfi plot of lbw around 1100 Mhz.
07feb06: gps L3 test on 06dec06. A2010 data.


04dec06: The 1548 Mhz birdie generated by the new cell phone detector
05sep06: A 1378 Mhz cfr, 3.2 Mhz wide radar appears for 430 seconds.
19jul06: punta salinas radar blanking test.
18jul06: az,za dependence of rfi  using transmitted birdies
17jul06: 1200 Mhz narrow birdie.
12jul06: 1188 birdie, 66 Mhz comb from kronos timecard reader
06jul06: birdie near 1320 Mhz.
07apr06: distomat birdies after window replacement
24feb06: compute the harmonics in the alfa/wapp receiver with cfr=1385.


30nov05:  compression in the alfa receiver with the 100 Mhz filter installed.
17oct05: location of 1350 faa radar aliases in alfa.
28sep05: 1300/1400 Mhz birdies coming from the wapps.
20sep05: cell phone harmonics in lbw when transmitting inside the dome.
01aug05: compression, baseline variation with long recovery in alfa (from faa radar).
12jun05: 1428 Mhz birdie in alfa 18may05 thru 23may05
08may05: aerostat compresses alfa receiver when oh filter bank amps were in.
27mar05: faa 1350 Mhz radar appears at 1380 Mhz in alfa survey data.
26feb05: punta salinas not staying in mode A


14dec04: 60 Mhz drifting harmonics at lband.
18nov04: measure the distomat birdies after some shielding work.
17nov04: punta salinas runs with chn 18 (1367/1382) on during the night.
04nov04: lband drifting 60 Mhz harmonics are not coming from the dome AC units.
14oct03: 1289.7 Mhz birdie for a1803 (punta salinas??).
06oct04: faa,punta salinas, and aerostat Radars. total power versus time.
28sep04: az dependence of faa radar compression in alfa receiver.
01aug04: alfa signal compression by the faa radar.
02jul04: 1400 Mhz birdies coming from 100 Mhz distribution/wapps
29jun04: birdies around 1400 Mhz while doing an azimuth swing.
11jun04: drifting harmonics in lband with 60 Mhz spacing.
30may04: distomat birdies after communications changed from copper to fiber.
28may04/07jun04: 1374.495 Mhz birdie.
28may04: 1400 Mhz birdie.


13oct03: 1422.5 birdie from tv channel 54
19sep03: lbw iridium signal stability.
29apr03. detect 1290,1350Mhz radars at 1ms with lbw.  Show rotation drift and compression
29apr03. IFLO (using lbw,lbn) compression by the 1330/1350 FAA radar .
13apr03. azimuth, za dependence of 1350,1290, and aerostat radars.
04apr03. Radar power levels in the downstairs IF (1290,1330/1350,punta salinas.


18sep02. Measuring the power levels at the output of the lbw dewar.
01mar02. 1400 Mhz biridie with azimuth swing


06nov01. 1381 gps L3 birdie on all the time.
05oct01. tone at 1350 Mhz.
04oct01. Radar harmonics created at the 2nd IF.
sep01-> rfi caused by new air conditioner.
20sep01 lbn. Rfi from color camera on the service platform.
02,08aug01 1400gr.rfi from tertiary electronics and motors.
02may01 1400gr. Measuring the power levels at the output of the lband wide dewar.
27apr01-11may01 1407gr. 300Khz wide birdie at 1407 (tv station).
26dec00 lbn. Birdies near 1420 MHz. Azimuth swings with dome at 19 degrees za.

03jan16: a2981 see 66Khz comb at 1667.562 Mhz

    A2981 took interim cor data at  the oh bands (looking at a comet).
The data  was 1 minute integrations using a hexmap pattern. Ellen reported a 66khz comb in the 1667 Mhz band.
Data was taken on :
Processing the data:

The plots show the daily spectral averages for 1667 Mhz  band (.ps) (.pdf)

processing: x101/160111/

20mar09: 1422.5 Mhz birdie from tv channel 54.

    Channel 54 is in the process of installing their digital transmitter. Some of the shielding around the transmitter has been removed to allow them to do this. The video carrier at 711.25 generates a 2nd harmonic at 1422.5 that we have seen in lband data.
    On 20mar09 an azimuth swing was done from az=180 to az= 413 at .1 deg/sec. Lbw in linear polarization and the 1370 hipass filter was used to check the rfi.  A 3.125 MHz band centered at 1423.4  with 1.5 Khz freq resolution was recorded using the interim correlator once a second (using 9 level sampling). The wider band was used to see if the 1424 Mhz birdie that has been reported recently was also coming from chn 54.
    Since the birdies are narrow band, a median filter of 34 channesl was used on each 1 second spectra to remove the bandpass.

    The plots shows the strength of the 1422.5 MHz birdie (.ps) (.pdf):
processing: x101/090320/

05sep06: A 1378 Mhz cfr, 3.2 Mhz wide radar appears for 430 seconds.    (top)

    0n 05sep06 around 3:43 am (ast) a radar appeared for about 400 seconds. The project a2010 was doing 600 second drift scans (1 second sampling) using alfa. The telescope was parked at az=360,za=4.2. The radar specs were measured to be:     The first image is the dynamic spectra   for beam 3 polA  (.gif) for the 600 seconds of data.     The 2nd plot has the average spectra and the time variation of the rdr (.ps) (.pdf):     What is the radar isn't:
processing: x101/060905/


18jul06: az,za dependence of rfi  using transmitted birdies. (top)

    To check if birdies are coming from the control room area you could compare the az,za dependence of the unknown birdies with the az,za dependence of known birdies from the control room.

    On 14jul06 birdies were transmitted from the control room and from the control parking lot. Data was then recorded with the lband wide receiver in linear polarization mode  while the dome was swung in azimuth and then stepped in za. The setup was:

    Various plots were made to show how the power varied. The azimuth swings were broken up into 4 90 degree plots to give better plot resolution. Each of the plots may have different vertical scales.
The plots show the az,za dependence of the xmitted birdies (.ps) (.pdf):
  Conclusions: To do:
Processing: x101/060714/

17jul06: 1200 Mhz narrow birdie  (top)

    Project A2049 was doing double position switching using lbw on 15jul06. The source A1852  (scans 619601431 - 1434) had a narrow birdie at 1200 Mhz. The birdie properties were:     The plots show the az dependence of the 1200 Mhz birdie (.ps)  (.pdf):     You can see that the 1200 Mhz biridie repeats for the same az, za. This shows that the birdie is not coming from inside the dome.

note on DPS pattern:

processing: x101/060715/

12jul06: 1188 Mhz birdie, 66 Mhz comb from kronos timecard reader.  (top)

    We are installing a new employee time card system made by kronos. The readers will be distributed at various locations at the observatory for employees to punch in. The current system was checked for rfi and found to have a 66 Mhz comb that extends through lband. The computer and reader are in a single plastic box.
    Data was taken on 12jul06 with the lband wide receiver to check if the rfi got into the receiver. The interim correlator was used with a 25 Khz channel resolution. Data was taken while the kronos device was in the control room and then when it was in the parking lot next to the control room. A few minutes of data was taken with the device on and then with the device powered off. There was no ethernet cable plugged into the device when the data was taken.
    The plots show the rfi created by the device at 1187.87 Mhz (.ps).  (.pdf) : processing: x101/060712/

06jul06: birdie near 1320 Mhz:   (top)

    project a2049 was doing double position switching with various sources on 06jul06 when a birdie close to 1320 Mhz appeared. The plots show the birdie near 1320 Mhz (.ps) (.pdf):     A dynamic spectra of the 15th scan (.gif) was made to show the frequency jump. What we know:
    processing: usr/a2049/

07apr06: distomat birdies after window replacement. (top)

    The windows on the distomat cans were replaced in feb/mar06. On 07apr06 lbw was used in linear polarization mode centered at 1400 Mhz with a 12 Khz resolution. 180 one second records were taken while pointing at each of the 6 distomats (the dome was at 18 degrees za). The 6 distomats were measured while moving clockwise and the 5 distomats were measured moving counterclockwise (we ran out of time to complete the ccw swing).
    The distomats were set to run on a 60 second measurement cycle so there were 3 complete cycles of turnon, turnoff while looking at each distomat. About 7 seconds after the minute the distomats begin their distance measurements. The data was synchronized to the start of the 60 second cycle. Birdies were seen at 1399.84 and 1400.01 Mhz.  I averaged the clockwise and counter clockwise swings. The plots show the current state of the birdies: The distomats with the birdies have not changed since the new windows were installed ( see  nov04 measurements). In nov04 the birdies lasted for a longer period of time. That is probably because the old screens were not as transparent as the new ones so it took longer to integrate up to the signal to noise that the distomats needed. The strengths look a little smaller in nov04. This is probably because the nov04 bandwidths were 25 Khz while the apr06 measurements used 12 Khz (the birdies are smaller than 12 khz).
    We looked  at distomat 3 with the portable spectrum analyzer and a we saw the 1400 mhz birdies. They were coming from the front of the distomat (through the window).
processing: 060407/

30nov05: Compression in the alfa receiver with the 100 Mhz RF filter in.  (top)

     A filter bank was installed in the RF after the alfa dewar. It has a set of switch able 100 Mhz filters centered at 1440 Mhz as well as the straight through option (no filter).  These filters should help reduce the compression of the system caused by the radars. The main culprit is the FAA radar at 1330/1350 Mhz.
    The faa radar specs are:

On 30nov05 data was taken with the wapps in pulsar mode with the 100 Mhz filters in. The setup was:

 The data processing of the data was: The plots show the results of the measurements:



28sep05: 1300,1400 Mhz birdies coming from the wapps.  (top)

    Narrow birdies have previously been seen at 1300 and 1400 Mhz (more info:  2004). Some of these birdies were found to come from the correlator/wapp room. During the summer of 2005 the shielding of the doors and the windows of the wapp/correlator room was worked on. Measurements were taken on 28sep05 to see any remaining signals.

    Data was also taken with the lbw receiver (in linear pol mode) using  the interim correlator. The correlator was set to 95 hz resolution (190 hz after hanning smoothing) . 2 bands were centered at 1300.001 and 1400.001 (the offset was used to get away from the spike in the center of the interim correlator). To verify that the signal was coming from the wapp/correlator room, the 100 mhz input reference for the wapps was taken from an hp synthesizer. Data was taken with the synthesizer locked to the station clock and also with the synthesizer free running. When in free running mode, the 100 Mhz frequency shifted down by 85.4 hz. This offset got multiplied by 13 and 14 to get to 1300 and 1400 Mhz. The plots show the results of the measurements:

processing: x101/050928/

26feb05: punta salinas transmitter left at wrong frequencies??  (top)

    On 26feb05 project A2010 was doing 100 Mhz drift scans centered at 1385 using alfa starting at 21:15 ast. Interference that looked like punta salinas radar was seen in the band. Punta salinas was called at 21:25 ast and they claimed they were in mode A (channels 2,3). The plot shows the hilltop monitoring 1325 Mhz band for 26feb05 (gif). Lighter color is stronger signal.
    Each punta salinas channel has two frequencies separated by 15 Mhz. Each channel pair is flagged with a different color.  For most of the day there was power in :

It seems unlikely that punta salinas was in mode a and someone else was using most of their channels...
The birdies at 1330/1350 Mhz are the faa radar. The 1290 signal is the remy radar.
processing: 050226/

18nov04: distomat birdies still there after added shielding. (top)
    The shielding for the distomats was worked on an then more measurements were taken. On 18nov04 lbw was used in linear polarization mode centered at 1395 Mhz with 24 Khz resolution. 180 one second records were taken while pointing at each of the 6 distomats (the dome was at 18 degrees za). The distomats were set to run on a 60 second measurement cycle so there were 3 complete cycles of turnon, turnoff while looking at each distomat. About 5 seconds after the minute the distomats begin their distance measurements. The data was synchronized to the start of the 60 second cycle. Birdies were seen at 1400 Mhz. The plots show the current state of the birdies: The distomats with the birdies have changed since the may04 measurements.
    On 29mar05 we went down and looked at distomats 3,4,5,6 using the portable spectrum analyzer and a helical lban antenna. With a 50 Khz span we saw the 1400 Mhz birdie in all of these distomats. It was strongest in D3,D5, and D6.
processing: 041118/

17nov04: 1367/1382 radar.. punta salinas chn 18 left running.

    On 17nov04 project A1961 had two radars at 1367 and 1382 Mhz. They observed during the early morning hours. A peak hold of a 162 second scan showed that this was punta salinas channel 18 which had been left on. The plots show the radar signature (.ps)   (.pdf). The hilltop monitoring showed that punta salinas was in mode A,B,C and channel 18 on from midnight 17nov04 till about 15:00 17nov04. This only occurred on 17nov04. 16nov04,18nov04 did not have this problem.
processing:  usr/a1961/

06oct04: faa,punta salinas, and aerostat Radars. total power versus time.  (top)

    On 06oct04 data was taken with pixel 2a,2b of the alfa receiver. The band was centered at 1410 Mhz. The front panel outputs were passed thru attenuators (pix2a 15db, pix2b 0b) and then detected with a 20 usecond time constant. The signal was then sampled at 10 usecond sampling for 48 seconds. The telescope was parked at az=270, za=1.9 degrees.
    The attenuated version was to let us see an unclipped version (in the A/D's) of the radar signal when it pointed at the AO.  The unattenuated version was to see detail when the radar was not pointed directly at us. These plots can be used as a reference when someone is looking at  a square law detected signal on the oscilloscope in the control room.


28sep04: azimuth dependence of faa radar signal using alfa receiver.  (top)

     The faa radar specs are:      When the radar beam points in the direction of the observatory  there is a large signal at 1330 and 1350 Mhz. Frequencies outside the 1330/1350 range go into compression (they decrease in power). The depth of the compression can be used to measure the strength of the faa radar in the receiver system.
    On 28sep04 an azimuth swing was done from az=270 to az=630 degrees. The azimuth moved at .3 degrees per second. The dome was at 18 degrees za. A 100 Mhz band  centered at 1420 Mhz was sampled every 64 useconds using the alfa receiver and the wapps. The alfa rotator was set to 0 degrees. The processing steps were: The first plots shows power versus time when the faa radar pointed at the observatory (.ps)  (.pdf) (using pixel 4 of the alfa receiver). The second plot shows the compression versus azimuth angle (.ps)  (.pdf) .

02jul04: 1400 Mhz birdie coming from 100 Mhz distribution/wapps.  (top)

    The 29jun04 measurements showed that the 1400 Mhz birdie was not coming from inside the dome. On 02jul04 eddie castro and myself looked in the control room with the new tektronix spectrum analyze (ybt250) with 100 hz resolution. The birdie was 20 to 30 db above the noise floor (100 hz resolution) in the receiver room. The signal got to 50 db above the noise floor in the wapp,correlator room. We did the following tests:
  1. We unlocked the phase lock loop for the 100 mhz distribution. This caused the birdie to drift by many khz.
  2. We pulled the power on the 100 Mhz distribution and the birdie in the receiver room went away.
  3. There were 3 cables leaving the 100 Mhz distribution: correlator, receiver room, and wapps. We replaced the 100 Mhz phase locked reference with a 100 Mhz from an hp synthesizer for these 100 Mhz (one at a time). We monitored the birdie in the receiver room while we did this. The portion of the 1400 Mhz birdie that came from the "different" 100 Mhz reference would jump be a few 100 hz (since the hp synthesizer was not synched to the maser). Of the 3 signals, the wapps had the strongest signal.
It's not surprising that the wapps had the largest contribution to the 1400 Mhz birdie since all of the correlator chips are running at 100 Mhz.

We spent some time looking at the strength of the signal outside in front of the control room. The results were:

29jun04:  birdies around 1400 Mhz during azswing.  (top)

    Birdies close to 1400 Mhz were looked at with high spectral resolution during an azimuth swing. The correlator was set to 190 hz resolution (after hanning smoothing). The telescope was swung from az=540 to az=180 and then back at .4 degrees per second. Data was dumped at 1 second intervals. Lbw was used in linear polarization mode with the 1370 hipass filter in. The two az swings took about 2000 seconds. Conclusions:

11jun04 drifting harmonics in lband with 60 Mhz spacing    (top)

30may04: distomat birdies still there after converting to fiber communications. (top)

The communications between the distomats and the control room were converted from copper to fiber in xxxx 04. On 30may04 I  checked to see if the distomat birdies were still present after this conversion.
    Lbw in linear polarization mode centered at 1400 Mhz with 48 Khz resolution (after hanning smoothing) was used. 180 one second records were taken while pointing at each of the 6 distomats (the dome was at 18 degrees za). The set of birdies used was at 1399.83 and 1400.00 Mhz. The distomats were running on a 60 second measurement cycle. About 10 seconds after the minute the distomats begin their distance measurements. The data was synchronized to the start of the 60 second cycle. The plots show the current state of the birdies: The conversion of the distomat communications had little affect on the distomat birdies that occur during the measurement (see 28apr02 measurements).
processing: 040530/

28may04,07jun04 1374.495 Mhz birdie. (top)

    Project a1861 had a birdie at 1374.495 Mhz. Lband wide was used in linear polarization's with the radar blanker enabled.. They did 5 minute on/off position switching. The correlator was setup for 2048 channels over 12.5 MHz and 1 second dumps. The birdie was less that 1 channel wide (6.1 Khz). The plots (ps)  (pdf) show the birdie during 4 on/off patterns (300*2*4=2400 samples). This birdie is coming from outside the dome. The birdie strength correlates with azimuth  position so it is probably ground based. It does not correlate as well as the 1400 Mhz birdie above and does not line up with the distomat locations.

On 07jun04 base band sampled data with 10 Khz bandwidth was taken to see the high resolution structure of this birdie. The image (.gif) shows dynamic spectra for 500 seconds. The bandwidth is +/- 245 Hz about 1374.494794 Mhz. The frequency resolution of the image is .6 hz. The  top plot is polA while the bottom plot is polB (lbw was set to linear polarization mode). The signal is drifting by about 5 hz over 500 seconds. The sidebands of the signal are spaced by 60 Hz. The instantaneous width of the line is less than 1 Hz wide.

processing: usr/a1861/, x101/040607/

28may04 1400 Mhz birdie.
    Project a1861 had a birdie at 1400. Mhz. Lband wide was used in linear polarization's with the 1370 wave guide filter in. They did 5 minute on/off position switching. The correlator was setup for 2048 channels over 25 MHz and 1 second dumps. The birdie was less that 1 channel wide (12.2 Khz). The plots (ps)  (pdf) show the birdie during 2 on/off patterns (300*2*2=1200 samples). There is a distomat located at an azimuth of 207 degrees (distomat 4). Normally the distomat birdies turn on for a few seconds every 120 seconds and then turn off. This birdie looks like it is on all the time.  The blowup of the polA birdie shows that it is the beam sweeping thru the birdie that makes it go up and down, and not the distomat turning on and off (that would not give a gaussian profile). We need to look at this with higher resolution.
processing: usr/a1861/

14oct03 puntaSalinas? birdie during a1803 experiment.  (top)

    Experiment a1803 has been having problems with radars at 1289.7 and 1298.7 Mhz. I took some data during the day on 14oct03 using lbn, the 1280Mhz hipass filter in, 25Mhz bandwidth with 1024 channels, and 209 1 second dumps. I covered 1278.5 to 1322.5 Mhz.     The 15 Mhz spacing looks like the punta salinas radar.  It also has a 12 second period like the punta salinas radar. It could be punta salinas channels  9 and 10 if their reference frequency was off by 3 Mhz. The bandwidth is a bit narrow but we may only be seeing the long range pulses (which are stronger and narrower in freq). I did not get a chance to measure the pulse duration of the signal. It went off of the air around 15:30. The temporal duration of the pulse should tell us if it really is a fps117 radar. By the way, I've notices that the faa airport radar has not been transmitting simulataneously at 1330 and 1350 Mhz (just one or the other). I wonder if they have changed their radar???
processing: x101/031014/

13oct03 Color camera #5 birdie at 1417  (top)

    On 16sep03 the dome camera #5 (looking at the klystron tube) showed a birdie at 1417.5 Mhz. The camera was removed and worked on in the lab. On 13oct03 it was reinstalled and tested using the correlator. The setup was lband wide, 2048 channels over 195 Khz (95 hz resolution) , with 1 second dumps. The image of the dynamic spectra  show the results. The camera was removed and returned to the lab for more testing. The question is how is the rfi getting out of our rfi shielded enclosure for the camera?
processing: x101/031013/

13oct03 1422.5 Mhz birdie from tv channel 54.

    A test was done with tv channel 54 to see if it was still generating birdies. The video carrier is at 711.25 Mhz. The 2nd harmonic of this falls at 1422.5 Mhz. A guard at the transmitter site opened and closed the transmitter doors while we were taking data. He also turned the transmitter on and off.  The lband wide receiver (Tsys about 28 Kelvins) was used in circular polarization mode. Data was taken with the interim correlator running in two modes:  381 Hz  and 95 Hz resolution. Data was dumped once a second. The plots show the results of the measurements.     A 1422.5 Mhz birdie is seen from the channel 54 transmitter. It is less than 95 hz wide. It has a maximum strength close to az=258,za=18 deg. Closing the transmitter doors makes a difference when the telescope is not in the maximum strength position. When the telescope is sitting close to the maximum strength position , closing the transmitter doors make little difference.
processing: x101/031013/

19sep03 iridium signal stability. (top)

    Experiment a1840 dumped 100 Mhz bands every 2 milliseconds with the bands centered at 1370,1470,1570, and 1670 Mhz while looking at interplanetary scintillation's. There were 256 channels per board giving 390 Khz resolution. 14 300 second integrations were done over two days. I used this data to see how stable the iridium signal was. The signal has a 90 millisecond period with 45 milliseconds for downlink ( more iridium info).
    The band of interest were 1621 to 1626 for iridium and 1610 to 1613 for the radio astronomy band. Unfortunately the observer setup the filters so they abutted at 1620 Mhz. The plots show the iridium signal properties.. The satellite signals look pretty stable with time. We can probably compute the phase of the start of the 90 millisecond cycle and then use the sps to generate a blanking signal. The blanking duration will probably have to be close to 50 milliseconds. As a double check, i need to find someone else's data and see if the phase of the signal from this data set continues to predict the phase of the iridium on cycle.


04apr03: Radar power levels in the downstairs IF (if2)   (top)

    The system was being driven far  into saturation so that the gain was decreasing during the radar pulses. I wanted to measure the downstairs IF power levels  when the radars were present to see if it was happening downstairs or upstairs. I set the power levels into the square law detector so that the largest pulsed from the radar would not clip. This meant that you could not see the off pulse noise floor.


The 1st sampled pair of 500 MHZ bandpass was taken from the 750 Mhz front panel output. This had a 20 db pad so the power level was the same as that measured by the power meter. It was sent to a square law detector and detected with a 2 usec time constant. This voltage was multplied by 5 in an opamp and sent to the 8 bit A/D converter (0 to 2.5 volts full scale).  The 2 signals (polA,polB) were sampled at 1 Mhz.

The noise power levels into the square law detector were -52 dbm so we could only see when the radar was on and pointing at us. This insured that the a/d square law were not saturated.

A second set of signals were taken from the bottom of the IFLO buffer amps. The output power of the buffer amps is 14db + gainUsed greater than the input power. The 8db gain used set the output power 22 db above the input power. The data was taken out of the front panel input, passed through 23 db of attenuation (to put the levels close to the first pair of signals) , detected,  and then sent to the AtoD converters.

The correlator ran at 1 second dumps, 3 level interleaved sampling 1225 to 1425 Mhz. This let us identify which radars were active.


To calibrate the system, a -20 dbm and then -17dbm tone at 750 Mhz was injected into the IF/LO at the transfer switch input (right after the FO rcvr output). This data was recorded and used to map the a/d levels into dbm in the downstairs if/lo. The power at the output buffer amps of the IFLO were 22 db above the input. The -20 dbm level would be + 2db output at the buffer amps.

The radars seen:

Three radars were seen: 1290 Mhz remy radar, 1330/1350 FAA airport radar, and the punta salinas fps117 frequency agile radar (the aerostat was not broadcasting). Each of these radars has a 12 second rotation period.  Three distinct peaks could be seen in any 12 second section of data. They occured when the radar pointed in our direction. The radar peaks were identified in the total power data stream by their  radar ipps (since they were known ahead of time).

The plots show polB,polA from the upper section of the iflo rack and then polA polB from the buffer amplifiers. A gaussian is fit to each sweep of the radar to measure the beam width as it passes in front of the observatory. The second page shows a single sweep (rotation) of the radar, ipps, and a single pulse.


The power levels from these radars are not close to the 1db compression level of the system (+16dbm for the amplifiers at the end). There is some compression occuring so it must be upstairs. The punta salinas 51 usec pulse may be going  negative. If this is true, it must be happening upstairs since the downstairs levels have not arrived at saturation.

    On 23apr03 we placed a 20 Mhz IF filter centered at 1435Mhz before the fiber optic transmitter. We  saw saturation with the 1350 FAA radar. We placed a 1435 rf filter before the  mixer and saw no saturation. This shows that the compression is occurring in the 750 Mhz mixer chassis.

18sep02. Measuring the power levels at the output of the lbw dewar.   (top)

    The power was measured at the output of the lbw dewar on 18sep02. The azimuth was stationary. Peak holds were done at 1300 Mhz 1Ghz bw and 1400 Mhz 400 Mhz bw.
(image missing)
(image missing)
Compare these plots with the data taken may01 from after the lbw dewar. This data was taken with a 30Khz Resolution bandwidth filter. The radar bandwidths are  .2 to 2 Mhz so this setting undersampled the radar power by up to 1.6Mhz/30Khz= 55 or 17 db low.

28apr02 Distomat biride at 1399.83 (top)

    Experiment A1475 (using lbn) had interference at 1399.83 with a 1 minute period. It repeated  in the on position and the off position. This occurred in multiple scans that were close to azimuth 175 to 191 deg. At the time the distomats were being run on a 60 second cycle. The rfi window had been installed on the distomats months ago. The plot shows the power in a 12 Khz channel at 1399.83 Mhz (black) and two adjacent channels 24 Khz away (red,green). The rfi is strongest in polB (upper plots). The data was sampled with 6 second intregations.
processing: usr/a1475/
  • 24may02 Color camera birdies still present.  (top)

  •    The dome color cameras were checked on 24may02. Camera #1 that caused the problem on 09apr02 was not installed (so there were only 5 cameras). The setup used a 390Khz setup with 190 Hz resolution. There was a band  at 1388.86 and a second band at 1417.5. lband narrow was used while tracking blank sky with the  radar blanker on. In the test all of the cameras were turned on/off using the downstairs switch.
        The first plot shows 200 seconds cameras on followed by 200 seconds cameras off. 10 20 second integrations were done with the camera on followed by 10 20 second integrations with the cameras off. The black trace has the cameras on while the red trace is the cameras off (both figures are polA). The birdie at 1388.858 went away when the cameras were turned off. The smaller birdie at 1388.86 was there all of the time. The lower figure shows the birdie at 1417.495. The smaller birdie at 1417.482 was only in one of the 20 records. The birdie was not resolved with the 190 hz resolution. The signal strength in the 190 Hz wide channels is about 23% of Tsys or (.23*28K)=6 kelvins.
        The second image shows 1 second dumps while the cameras were turned on and off. The horizontal axis is frequency while the vertical axis is time (in seconds). The dashed horizontal lines are where the cameras were turned on or off. The cameras had been on for awhile before the test started. You can see that when the cameras were turned on, the birdie drifted by about 2 Khz. After 100 seconds it had still not come back to the frequency we started with. This is probably a temperature related drift when the power gets applied.

           Two birdies were found: 1388.858 and 1417.495 with a spectral width < 190 Hz. This would be a comb frequency of 14.3185 Mhz (corrsponding to the comb measured before shielding..see 20sep09). The other members are probably also present. I had initially used 25Mhz/1024lags =  25 Khz resolution to look for the birdies. With this setup you couldn't see these birdies in 1 second dumps. The frequencies drift up to 2 Khz when there power if first applied.  When debugging this problem you will need to use the high frequency resolution.

    processing: x101/020524/

    09apr02 rfi from color cameras in the dome. (top)

        Rfi at 1417 Mhz appeared in early apr02. Turning off the color cameras in the dome made the birdie go away. On 09apr02 the 6 cameras in the dome were turned off 1 at a time (by disconnecting the power to the camera). The correlator was run with a 6 Mhz by 2048 channels setup with 1 second dumps on lbn receiver. The plots show how the rfi at 1417 changed as each camera went on off. The problem with camera 1 was not there on 20sep01 so something must have changed since then. Maybe the shield on the cable that goes out to the camera has a break in it somewhere. Camera 1 should be left off until it is fixed. We also need to do a better job of shielding the other cameras.
        Note: 30jul02 the gasket material used to make good contact for the doors of the camera box degrades with time. see 2 mhz comb at 327 Mhz: resolution.

    01mar02 azimuth swing with 1400 Mhz birdie (top)

        On 01mar02 I did an azimuth spin with the dome at 18 degrees za ]moving at .4 degrees/second. The azimuth spin plot shows that the peak strength is in the azimuth direction 340 degrees (toward the control room). This is the same direction found for the peak of the 1350 Mhz birdie.

    28feb02 1400 Mhz birdie. (top)

        3 On/off scans of 5 minutes each were taken with lbn. The plots show a 1400 Mhz birdie. The resolution was 6 khz and it is not resolved (on 01mar02 I used 190 hz channel width and it did not drift and it was not resolved). The birdie divides out between the on and the off so it is very stable. The distomats were turned off during the off of the first scan. The times (seconds from midnite are:

    06nov01. 1381 gps L3 birdie on all the time. (top)

        There has been a birdie at 1381 Mhz  for the last few weeks that is 1 Mhz wide. It looks like GPS L3 at 1381.05 Mhz but occurs more often than the scheduled usage of GPS L3. The people at the VLA do not see this unusual usage of GPS L3.
    Experiment # A1517 has been running from 19:00 AST thru 1:00 AST the next morning. Below is a list of what it has  seen at 1381. The dates are the AST end dates (1am AST). The times are AST (UTC-4). 06nov01 was different from all of the other days. On this day, the bursts would last for a minute or two but the signal would not turn off completely after the bursts. A low level interference would remain on.

    The figure shows two plots from 06nov01 when the birdie was on all the time and 1 plot from 08nov01 when the bursts were normal. The data was sampled at 1 second intervals. The telescope was tracking a celestial source while this data was taken on 06nov01. On 08nov01 the telescope was stationary while the data was taken. (The links for fig1,2,3 below are the the individual pages from the "figure" link above. They were added for the braindead browser at aerospace!!)

        GPS L3 is used for nuclear blast detection. There are on board sensors that monitor electromagnetic and x-ray events that could be related to nuclear blasts. Using multiple satellites, the positions of the blasts can be determined. This data is formatted and transmitted to ground stations on the L3 frequency. The GPS Nuclear Detection System operators were contacted and they admitted that one of their birds had a problem with its detector being stuck on. This could have caused the continual transmissions that we were seeing on 5/06nov01. A single satellite failure would also explain why we saw it and the vla didn't.


    05oct01. tone at 1350 Mhz. (top)

        The FAA radar is at 1330 and 1350 Mhz. When the radar blanker was used, the radar pulses were blanked but a tone remained at 1350 Mhz. On 05oct01 an azimuth spin was done with lband narrow (native circular) with the dome at 19 degrees za to look for any azimuth dependence of the tone. The correlator was setup for 25 Khz resolution and was dumped at 1 second intervals. The figures shows the results. Pol A is black, pol B is red, and the azimuth location of the control room is flagged with a green vertical line.     The tone is between azimuth -100 and +10 degrees az. The peak value is close to the control room values but the center is not.  The peaks last for about 8 seconds (or 1.6 degrees in azimuth). At 25 Khz resolution the tone was not resolved.

        If the control room is causing the problem, then the center offset may come from the asymmetry in the cliffs adjacent to the control room blocking the beam. The lidar lab and the rfi shack are also in this general direction. We need to go up to the azimuth with an antenna and look around (bringing the data down into the correlator and using the blanker).

    04oct01 Radar harmonics created in the 2nd IF. (top)

    13aug,20sep01 lbn. Rfi from color camera on the service platform. (top)

        A color camera  was placed on the service platform for monitoring purposes. It had no "extra shielding" added by us. On 13aug01 the lband narrow receiver was used to measure the rfi from the camera. 1337 to 1437 in 4 subtends was used. Each with 25 Mhz over 1024 channels. 1 second integrations were done. 120 seconds of data with the cameras on were followed by 120 seconds with the cameras off. The camera was removed and shielded. The rfi was remeasured on the service platform on 20sep01 using the same setup but a 240 second integration.     The image shows that the frequency is moving by up to 100 Khz/second. This will decrease the average intensity of the tone when averaged over time.
    A fundamental of 14.3341 would give harmonics at the measured positions. The strength of the signal increases every 4 of these units so there are probably two frequencies involved.
    The shielding removed the rfi for a 4 minute integration. To go farther in sensitivity we should do the experiment at night (no sun and hopefully no punt saloons radars).

    02may01 Measuring the power levels at  lband wide dewar output.  (top)

        We measured the output power levels of the lband wide dewar using the 22 Ghz spectrum analyzer and a power meter. The telescope was parked at az=214.4 and the gregorian was at 19 degrees. A 12 foot long semi rigid cable was used to connect to Pol A's output.  The plots show:

    27apr01-11may01 1407 Mhz birdie from tv station. (top)

    A 1407 Mhz birdie appeared in apr01. It was about 300 Khz wide and seemed to be on all the time. Some of the characteristics of the signal were measured using the lbw receiver in the dome:
    22jan01 distomat birdies at 1300,1400 Mhz.    (top)


        The distomats used for the laser ranging were generating birdies around 1300 Mhz. To measure this the correlator was setup for 25 Mhz bw/1024 channels centered at 1295 Mhz using the lband wide system. The telescope was pointed at each distomat in turn (n*120 +/- 35 degrees az, za=18 deg).  The distomats were run on a 30 second cycle starting on the minute. The correlator integrated for 180 seconds looking at each distomat separately. The distomat program spends about 7 seconds reading the temperature and tilt sensors and then it starts reading the 6 distomats. The measurement is usually through in 22 seconds.
    processing: x101/010122/
    26dec00 lbn. Azimuth swings with dome at 19 degrees za
    .  (top)

    A 3 Mhz band pass was used. Swings were done centered at 1420 Mhz (257 10 second dumps) and  1419.5 Mhz (284 10 second dumps) The plots show :
  • Figure 1: The  (average - baseline ) for each of the swings (pol Apollo B separate).    The birdies are at: 1419.36,1419.5, 1419.93, 1420.00,1420.8.
  • Figure 2: a blowup of figure 1.
  • Figure 3: The 1420 Mhz birdie channel versus azimuth angle with adjacent off channels over plotted. The bottom plot shows the difference between the 1420 Mhz birdie channel and the adjacent channels. There does not appear to be any azimuth dependence so the birdie is probably generated inside the dome (although the tsys bumps at -60, 60, and 180 which are perpendicular to the triangle sides are very interesting!!)
  • processing: x101/001226/

    rfi measurements home: