6900 to 7050 rfi in cbhi
Project A2765 (chris salter) saw some strange rfi in the cband
receiver on 11mar13 and again on 16mar13. The setups were:
- cband high receiver
- 11mar13: 1 ghz band centered at 6500 MHz
- 16mar13: 1 Ghz band centered at 7500 MHz.
- Mock spectrometer.
- 86MHz Bandwidth * 14 bands
- 1 second integrations
- 300 second scans (at least those with the rfi).
- The telescope was tracking sources and off positions
- 11mar13: peak rfi az=109.3,za=18.5 deg
- 16mar13: peak rfi: az=181.2, za=5.1 deg.
Dynamic spectra of 86MHz bands with rfi:
- 11mar13 6990 band (.gif)
- The large rfi starts around 60 seconds and last for about 10
- there is a precursor at 40 seconds.
- the dynamic spectra has been normalized to the median
- This is why there is a brighter stripe where the rfi was
on for ashorter period of time.
- 16mar13 7012 band (.gif)
- The rfi starts around 70 seconds.
- There looks like a weaker set around 270
Line plots of rfi:
The first set of plots shows
the timing, variability, and frequency variation of the rfi
The 2nd, 3rd sets of plots shows the 1 second spectra around the rfi
- Page1 : time variation of the rfi.
- 11mar13 rfi. average 6980-6985 MHz and then plot versus
- frame1: full scale
- frame2: blowup in time and amplitude
- The strong rfi lasts for about 8.6 secons
- there is a precursor about 23 secs before the strong rfi
- 16mar13 rfi. average 7020-7025 and then plot vs time
- frame 3: full scale
- frame 4: blowup
- The strong rfi lasts for about 18.8 seconds
- The rfi on the 16th was about 10 times weaker than the rfi
- Page 2: rms/mean for the 300 seconds of each scan, covering
the 1ghz bands
- Red in polA, green is polB
- Top frame: 11mar13 with rfi 6900 -> 7000+
- Bottom frame:16mar13 with rfi 6980->7050
- Page 3: overplot the spectra with the strongest rfi for both
- Each spectra was normalized to the median value for the scan
- the red,green traces were taken on 11mar13
- The blue,purple traces come from 16mar13
- The veritical dotted lines are placed every 19.43 MHz.
- The "on freq" is 13.00 MHz wide, the "Off freq" is 6.43
- The "off freq" period is about 1/3 of the cycle.
- rfi was seen in the cband hi reciever on 11mar13 and again on
- The rfi covered 6900 to 7050 MHz (each day covered a part of
- The rfi was on for:
- 11mar13: 8.6 seconds. It had a precursor about 23 seconds
before the main rfi
- 16mar13: 18.8 seconds. The same around appears about 200
seconds later (but much weaker).
- The rfi has a period of 19.43 MHz
- 13MHz on
- 6.43 MHz off
- The off Freq is about 1/3 of the period.
- This periodic rfi was seen back on 25sep12.
- Looking at the FCC allocations,
- Non Federal table:
- 6875-7025: .. (note NG is Non Government).
- FIXED NG 118
- FIXED-SATELLITE (Earth to space), (space to earth)
- MOBILE NG171