Gps L3 test dec06
There was a scheduled test of the GPS L3 communications band on:
During this period, project a2010 took spectral line data from 19:30 to
22:30 (AST) on 06dec06. The observation used:
dec05 17 to 25 hours (ast)
dec06 17 to 25 hours (ast)
The plots show the gps L3 occurrence in the data.
alfa receiver 7 beams by two pols in drift mode
100 Mhz by 4096 channels centered at 1385 Mhz
1 second averages
Each strip was 600 seconds of data followed by a calibration scan
The first plot averages
1 MHz of data about 1381.04 Mhz (.ps) (.pdf)
(this is the center of the GPS L3 signal). Each point is a 1 second average.
A 2nd order baseline was removed from each 1 second 4 Mhz sample before
computing powers or baselines.
spectra of the first 600 seconds (.gif):
Top 1 Mhz avg about 1381.04 vs sample number:
There are 14 data sets (7 beams times two polarization's). They have been
offsets for display.
The horizontal access is sample number. There are 18 strips * 600 samples
The signal was on nearly continuously for the first five strips. It reoccurred
near sample 6500 and 9000 (but only for a short duration).
Center. This is the power computed over the 4 Mhz baseline (excluding gps
and the 1380 birdie). It shows that there were no jumps in gain/power.
The increases in the top plot are coming from the gps signal.
Bottom: This is the same plot as the top one except that it is plotted
versus AST time rather than sample number. The continuous interference
was over by 20:30 AST.
second averaged spectra (.ps) (.pdf):
The horizontal axis has 6 frequency bands each of 164 channels (4 Mhz).
They correspond to beam0a,0b,1a,1b,2a,2b. Vertical dashed lines show the
start of each band.
Each band of 164 channels covers 1379 to 1383 Mhz (center of 1381.04).
The vertical axis is time in seconds.
The rfi occurring every 12 seconds is a harmonic (in the IF) of the
You can see the 1381.04 1 Mhz wide gps l3 signal change with time. It is
present in every 1 second integration. There appears to be a vertical striation
that you seen when L3 is strong.
11 seconds of data from beam0a have been averaged. The data is centered
on second 565 of the dynamic spectra (where GPS L3 was strong and the striations
The small bump at 1380.1 is the 1350 faa harmonic.
Vertical dashed lines are shown every 120 Khz. They are close to the striations
in the image. This would correspond to a time modulation of 1/120e3 = 8.3
useconds. I'm not sure whether this is part of the GPS L3 modulation
scheme or not.