Gps L3 in a2010 data jan09-mar09
18jan09
The a2010 data from jan09 thru
mar09 was searched for some examples of the gps l3 signal.
A2010 has taken 1596 600 second scans (260 Mb each) in the first
3 months of 2009.
The search consisted of:
- Search the rms database computed each month. This holds the
rms/mean for each scan taken by a2010.
- Choose scans who had large values in the rms around 1381.05 MHz.
- Make images of these scans and pick 11 scans that had:
- strong values of gps l3 --> it came closer to the beam.
- Pick some scans where the sidelobes extended over +/- 15
MHz.
- pick some scans where the signal was weaker but it lasted for
a long time.
Data taking:
a2010 uses the following setup:
- The 7 beam, dual linear-pol alfa receiver is used. It has a
system temperature of about 28 Kelvins.
- Each beam is 200 arc seconds. The 7 beams cover about 10
arcminutes on the sky.
- The receiver is centered at 1385 MHz and a 100 MHz Bandwidth is
used.
- The telescope sits at the meridian during datataking.
- The wapp autocorrelator is used for datataking.
- Spectra are integrated for 1 second using 4096 channels. The
spectral resolution is 48 Khz after hanning smoothing.
Data processing:
- Dynamic spectra were made of the 4096 channel by 600 second data
sets.
- The image is divided by the median value to flatten the band
pass
- The image is scaled so that full scale (min to max
brightness) is +/- 2% of Tsys (+/- .6 kelvins).
- The image has been averaged by 4 in frequency (didn't have that
many pixels on my display!!).
- Individual spectra:
- Individual spectra showing gps l3 were 1 second in
duration. They were normalized by adjacent spectra that did not include
gps l3.
- Peak power in the gps l3 band
- The peak power in the frequency channels 1380.3 to 1381.8 was
found for each 1 second spectra (this has the 48 Khz Resolution).
- The 600 second points were then divided by the median value to
normalize it to the average spectral density (note the 500 second long
gps l3 scan used the 100 seconds when gps l3 was off for the
normalization).
The strongest signal 20jan09.
- On 20jan09 around 3:18 am (ast) the largets gps l3 value was found
- It has a peak value of 140 times the average spectral density
(both used 48khz rbw).
dynamic spectra 20jan09 (.gif):
- The image has 3 separate bursts.
- 3 peaks with lots of sidelobes occured at 10,84, and 120 seconds.
- that Large signals occurred at 10,84 and 120 seconds
- The sidelobes extend from 1360 to about 1395 MHz.
individual spectra/peak power for
20jan098 (.ps) (.pdf):
- Page 1:
- top: peak power near 1381 MHz. At 84 seconds polB got to 130 *
Tsys.
- Middle: blowup up the vertical scale. The burst at 350 seconds
lasted for 41.5 seconds and was about 5% of the average Tsys.
- Bottom: blowup horizontal and vertical.
- Page 2: average spectra second 84 for the 7 beams.
- beam 5 had the strongest signal.
- Page 3: blowup vertical scale for second 84 7 beams.
- You can see the sidelobes clearly out to the edge of the plot
- Page 4: Blowup second 84 beam 5 ..
- The dynamic spectra above used beam 5b (red trace). This is a
blowup of the strongest signal.
Other days with strong signals:
This shows some of the other days that had
interesting gps l3 signals. They are not uniformily spaced in time
because a2010 did not take data very often in mar09.
Dynamic spectra for the scans:
peak power at 1381 vs time for the 11 scans
(.ps) (.pdf):
Processing: x101/080408/chkgpsl3.pro
page up
home ~phil
