a2048: GPS l3 remains on
Project a2048 took data on 04apr18 01:37 to
05:13 UTC using alfa and the mock spectrometers. They reported GPS
l3 interference for most of the run.
Their setup was:
- alfa and the mock spectrometers covering 1220 to 1520 Mhz
- 1 second integrations
- 9 x 1200 sec scans. ( i ignored the cal scans)
spectra for the 9 data scans
The table below identifies the different rfi bands
|Scan start time
|Punta salinas radar
|galileo satellite E6 band
Total power GPS L3
The average power 1381.05 +/- .5 Mhz was computed
for each 1 second spectral sample.
The data was normalized to Tsys when the rfi was off.
the plot shows the GPS L3 frequency
power vs time (.ps) (.pdf)
- The data is plotted vs time (HH:MM:SS UTC).
- The colors are the 9 different 1200 second scans.
- the satellite transmission was off when the level dropped to
- this shows that the satellite transmitted almost continuously
for the 3+ hours.
Location of satellites
The GPS satellites are in 1/2 sidereal orbits
(every l1.x hours). (not sure about galileo).
Plots were made of the az,za (relative to AO) for each
satellite of the GPS and galileo constellations. The
pass selected was the closest to the observation times (00:00 01:00
The right side of the plot labels the satellite and the AST
date/time for the closest approach of the pass.
constellation (.ps) (.pdf)
glonass constellation (.ps) (.pdf)
- These are source azimuths (directions of the satellite).
- the source azimuth,za for the telescope varied from
az:210 to 250, za:10 to 18 degrees.
The final plots shows the
GPS satellites that were above the horizon during the
observation (.ps) (.pdf)
- Since the GPS L3 rfi was present for the entire time, I only
kept GPS satellites that were above the horizon for the entire 3
- Page 1: Angular distance between GPS satellite and arecibo
beam vs time.
- None of the satellites were particularly close.
- GPS19 was the closest to the beam (27 deg) at the start of
- Page 2: az,za of the satellites during the observation period.
- the red + lines at the bottom show the az,za (source) for
- Page 3: AO azimuth of the satellites during the observation.
- dashed red lines are perpendicular to the sides of the
- It is easier for a source perpendicular to a triangle edge
to scatter into the dish and up into the dome.
- None of the satellites stayed close to 60,180,300 degrees
for the entire time.
- GPS l3 remained on for 3+hours on 04apr18 utc 01:37 to 04:53
- this was seen in the alfa data taken at this time.
- The assumption was that a single satellite was causing
- There had been no notification of a test.
- If it is a single satellite, it is probably one of the 7
- none of the GPS satellites were within 27 degrees of the
- We also saw galileo interfering at the E6 frequencies : 1278,
- The 1268 interference was probably the chinese beidou
- To eliminate satellites from consideration, we need more data
during another pass.
- I checked the a2048 data on 01apr18 and 06apr18, but no
constant GPS L3 transmission was seen.
processing: x101/180404/gpsrfi .pro