Project A2335 (gass)
reported rfi at 1360 MHz on 12aug11 thru 14aug11. The radar blanker was
on when this data was taken (with the interim correlator). It was
reported as narrow band with variable amplitude.
15aug11 take data while sitting.. freq
On 15aug11 test data was taken with the mock
spectrometer to learn something about the rfi. The setup was:
- azimuth=234.34, za=11 10:30 am
- lband wide using linear polarization and no filters. The radar
blanker was not used.
- The faa radar was only broadcasting at 1330 MHz (1350 was
- The aerostat, remy radar, and punta salinas were broadcasting.
- The spectrometer setup used 1 second averages,8192
channels, for 523 seconds. 5 different bands were used:
- The center frequency differed to separate out birdies from
within the mock box.
- 39, and 77 KHz biridies are generated inside the box. By
changing the rf cfr, these birdies end up at different rf frequencies
so they can be identified.
The plots show the spectral output
- Page 1: 523 second spectra averages:
- The data was averaged for 523 seconds and then a bandpass
correction was removed.
- Top: 1359.75 to 1360.32 MHz polA blotted for each of the
- The colors are the different spectral resolutions
- The dashed purple lines are the common rfi that comes from
outside the mock box. The other lines are being created inside the mock
- Bottom: the 42 Hz resolution band
- Black is polA, red is polB
- the dashed purple lines are the rfi.
- Page 2:
- Top: blowup of strongest birdied (1360.016) averaged for 512
- polA is stronger than polB
- The total width is about 1400 Hz.
- overplot 10 second averages around 1360.016 birdie (polA).
- The lines have been offset for display.
- The 10 second width is about 900 Hz.
The dynamic spectra for the
narrowest band shows the drift in the rfi frequencies (.gif):
- This shows the 1360.014 and 1360.065 birdies
- You can see the drift in the birdie frequency vs time
- both birdies drift together.
16aug11: azimuth swing
On 16aug11 two azimuth swings were taken. The setup
- azimuth: 265 to 630 at .35 deg/sec and then back. za=15 degrees.
- radars active: faa,1330,1350, remy:1270,1290, punta salinas mode
- lband wide setup with linear polarizations.
- Mock spectrometer setup:
- 1 second sampling
- bandwidths:.344,1.72,3.44,28.67, and 172.032 Mhz
- center freq: 1360.053,1360.058,1360.063,1360.068,1300.
- a constant 1.008 Mhz was added in the digital mixer to arrive
at the above band centers.
- This moved the DC spike in the center away from the rfi of
dynamic spectra shows the 1360.015 birdie vs azimuth for the CW swing
- The median value of each swing was used for the bandpass
- The drifing frequency was also seen with the telescope sitting
- The signal goes away for many azimuths.
- The .344 Mhz band with 42 hz resolution was used.
- The peak value about the 1360.015 Mhz birdie was recorded and
then divided by an baseline average away from the rfi.
- The peak values for the clockWise CW and CounterClockwise
CCW az swings were then overplotted.
The plots show the results of the
azimuth swings (.ps)
- Top: polA 1360.015 peak for CW (black) and CCW (red) swings
- 2nd: polB 1360.015 peak for CW (green) and CCW (blue) swing
- 3rd: Blowup about az=-65 showing locations of all peaks
- bottom: Blowup about az=-30 deg showign locatiosn of all peaks.
- The clockwise and counter clockwise peaks overlay each other so
there is a variation of signal strenght with azimuth.
- the 1360.015 rfi has a strong azimuth dependence
- The polA and polB peaks occur at differnent azimuths (this is for
- polAPk: -69.45
- The peak value gets up to 7*Tsys in 42 Hz resolution.
- narrow band birdies were found at:
RFI Frequencies and
- Each birdie is about 900 Hz wide
- Looking at 1 second spectra, there is a peak at each edge of
the 900 Hz and a dip in the middle.
- the birdies drift in time:
- a few hundred Hz over 500 seconds
- The spacing between the birdies is about 49.5 KHz (or a multiple
of two times this).
- There is a strong azimuth dependence of the birdie strength.
- This implies that it is not coming from inside the dome.
- The azimuth values for the peaks (when dome za=15) is:
- polAPk: -69.45 deg
- polBPks:-85.78,-65.77 deg
- -65.77 polB was the strongest