Intro
On 10dec21 we took 4 scans each with 60
seconds of data. The scans pointed at azimuths of: 180,270,0,
and 90 deg (South,west,north, and east). The 15 db pads
were still installed at the inputs to the sband rf box in the
pedestal. We want to install a new rf bandpass filter to
get rid of the strong rfi, so we needed plots of the strength
and location of the current rfi.
Setup:
The 12meter sat a a particular azimuth
(180,270,0,90) for each scan. The elevation was set to 45
degrees.
- At each scan we took 2 x 172 MHz bands of data.
- The band centers were : 2260 and 2340 MHz
- We moved the centers so Dc (center of the band) was not
close to the rfi.
- the current rf filter in the 12meter sband rf goes from
2185 to 2364 MHz
- Power levels used:
- udc attn: 15 15 db
- if2 attn : 0 0
- if2mp gave -42 -46 dbm.
- The 2 mock spectrometers used were set to 172MHz bw,
.1 second dumps, 8192, channels, an a/d rms of 60 counts.
- 60 seconds of data was taken at each azimuth direction.
Processing the data
- The file for each scan was input (as a double), and the
600*.1 sec spectra were averaged.
- Normalizing the spectra to average Tsys (outside of the
rfi)
- A mask was setup to exclude the large rfi and then he
median value was then computed for these regions.
- The median values were then used to scale the specdtra
so that Tsys=1.
- The spectra were then changed to db's (above Tsys)
Looking at the data:
The plots shows the sband spectra (.ps) (.pdf)
- The spectra had the 15db pad installed before the rf box
in the pedestal.
- Top plot: 60 second average spectra PolA
- Bottom plot: 60 seconds average spectra PolB
- The colors are the azimuth direction for each 60 sec
spectra.
- There are 2 spectral bandpasses for each direction
(with some overlap)
- The vertical scale is db above the average Tsys (taken in
the rfi clean region).
- Page 1 full band
- The dashed line at 2370 shows where the current rf
bandpass filter starts to fall off.
- The rfi at 2320 MHz in leftmost spectra is an IQ image
of the rfi at 2200 MHz.
- Page 2 blowup around 2350 rfi
Summary
- The sband spectra show where the large rfi signals are in
the sband portion of the 12meter receiver.
- The peak rfi at 2350MHz is about 44db above the Tsys
value.
processing: x101/211210/sb_rfi.pro