atm digital receiver (echotek card)
sep,2005
Contents:
Intro:
History:
Linux config:
30mar06:
echotek config error caused IQ imbalance.
sep05: glitches (out of order ipps) in the data.
sep05: baud transitions show power overshoots
Intro: (top)
The echotek card is used to filter and sample the aeronomy
signals. It plugs into the pci bus. The 30 Mhz IF is sampled at 80
Mhz and then reduced to 5 or 10 Mhz bandwidth. The card returns 16 bit
complex samples. The card operation is:
The sampling is normally triggered by the transmitter rf pulse (from the
sps).
BurstCount samples are acquired and shipped to the cpu. This value
is user programmable. It needs to be a multiple of 4096 bytes.
A linux driver runs a dma chain that tells the echotek where to put the
data. There are two buffers that the driver loads.
The data taking software grabs a completed buffer from the kernel. It selects
a portion of the input data and moves it to one of two output buffers.
A tx section, height section, and noise section are selected. This selection
is needed so the i/o rate to disc is manageable. The number of output buffers
is currently set at two (but it can be increased).
A separate thread takes the full output buffers and writes them to disc.
The data files contain an ascii primary header followed by a set
of records (or tables). Each record contains an ascii header followed by
a number of ipps of data. This is typically 100 ipps. At 10 millisecs per
ipp each record holds 1 second worth of data. Files are filled with an
integral number of records until the 2 Gb limit. New files are created
automatically. Data should be continuous across files.
Glitches (out of order ipps) in
the data. (top)
Out of order records (glitches) were found in
test data taken 11aug05. The glitches appeared to be aligned with the 1
second records.
see: 11aug05:
out of order records in the 11aug05 test data.
More test data was taken on 07sep05. This data did not
show any of the jumps seen in the 11aug05 data.
see: 07sep05:
test data shows no out of order records.
The differences in the echotek card configuration for the two data sets
was:
-
The burstCount. On 11aug05 it was 50176. On 07sep05 it was 46080.
-
The card configuration for the bandwidth. On 11aug05 the card provided
5 Mhz of bandwidth. On 07sep05 it provided 7.5 Mhz.
The IF configuration was also different on the two days. On 11aug05 the
sampled signal was centered at 434 Mhz. On 07sep05 it was centered at 430
Mhz. Since the transmitter samples were always at 430Mhz, the
11aug05 had the tx samples offset by 4Mhz from DC. This made the
tx samples look different, but should not have had any affect on the records
being out of order.
sep05: baud transitions
show power overshoots
The transmitter is phase coded
with a barker and random shift register code (clp). On 07sep05
the atm digital receiver recorded power and coded long pulse
ipps. The data was output as 10 Mhz complex samples. The bandwidth was
7.5 Mhz. The plots show the
transmitter response to these transitions (.ps) (.pdf)
:
-
Fig 1: The transmitter samples for the power profile. It uses a 4 usecond
barker code. The data samples are every .1 useconds. The colors are:
Red voltage I, green voltage Q, black scaled power.
-
Top: 1 complete barker code. The dashed blue lines are blown up in the
lower plot.
-
Bottom: This is a blowup of the top figure. The transition takes about
8 samples (.8 usecs). The power (black line) overshoots by about 50%, goes
close to 0 (as the phase goes thru 0), and then stabilizes.
-
Fig 2 top: The transmitter samples for an entire coded long pulse tx window.
This used a 1 usecond baud.
-
top red: the I voltage sample
-
2nd green: the Q voltage sample. Most of the overshooting is occurring
in this signal.
-
3rd black: The scaled power. The data between the dashed blue lines are
blown up in the bottom plot.
-
Bottom: This over plots the voltage and scaled power for 8.5 useconds.
The power is also overshooting by about 50% before doing the transition.
It is taking about .6 useconds.
processing: x101/050907/txsamples_07sep05.pro
linux software config
05apr06:
logfile are not being written?,
ntpd not running system clock is 5 seconds fast.
/etc/cron.daily is running slocate every morning at 3:01.
History:
05apr06: ntpd has not been running. system clock is fast by
5 seconds.
05apr06: cron.daily has been running slocate at 3:01 every morning. This
should probably be removed.
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