11apr05 p2030 compression with new rf amps and the wapps
are not starting together.
P2030 is the pulsar consortium
search project. They are using 100 Mhz (3 level sampling) centered at 1420
Mhz. They sample 256 lags every 64 useconds and then the polarizations
are added before writing to disc.
On 09apr05 extra amplifiers were added to alfa before
the first mixer. Data taken on 11apr05 was used to see how the compression
of the system was being affected by these amps. Total power was computed
for the first 12 seconds of the first few scans done on 11apr05.
The data was averaged by 10 (down to 640 usecond sampling) and then normalized
to the median value over the 12 seconds. The data is plotted vs time with
each pixel offset for display purposes. The units are Tsys.
The plots for 6 scans are (you'll have to rotate by -90 deg in acroread
to straighten them out.. sorry..):
The negative going power is compression in the system.
After smoothing by 10 samples the signal is still compressing by 10% of
tsys. You can see the compression dissappear for 1.2 second and then
come back strong. This is caused when the aerostat blanks its transmitter
in our direction. The compression is lasting for a large fraction of the
12 second radar rotation period.
A blowup of 30 millisecs of data (at 64 usecs resolution)
shows the individual radar pulses match the spacing of the 7 aerostat ipps:
The strucuture caused by the compression gives you a
reference for aligning the 7 alfa pixels in time. The plots 2,3, and 4
show that the data in the 7 pixels can be off by 1 second. All of the wapps
are not starting at the same time. The headers for the individual
wapps have start times that correspond to these differences (so the timing
has no been lost). Of the 31 search scans taken on this day, 12 of
them had these offsets.
(.pdf) : The dashed vertical lines are the 7 ipps of the aerostat
radar. They line up with the compression periods. The compression is up
to 40% of Tsys (with no averaging). It lasts for about 5 samples (320
usecs). The pulse length of the aerostat is 2*160=320 usecs long each ipp.