Gps L3 test dec06

• dec05 17 to 25 hours (ast)
• dec06 17 to 25 hours (ast)

• 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.

•  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 per strip
• 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.

• 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 1350 radar.
• 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 were visible).
• 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.

page up
home ~phil