Glitches in the atm digital receiver: test data 11aug05

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The setup:

• The transmitter was cycled between power profiles (10 seconds) and coded long pulse (10 seconds).
• The RF  was centered close to 434 Mhz.
• The ipp was set to 10 milliseconds.
• A single channel data  (complex 16 bit I/Q)  sampled at 10 Mhz bw were recorded.
• Data was written in the .shs (simple header system) data format. Each file had:
• An ascii primary header
• multiple records containing an ascii data record header followed by 100 ipps of binary (short) data.
• Each recorded  ipp  included:
• 560 useconds of transmitter samples (5600*2 shorts)
• 4000 usecs of height data (40000*2 shorts)
• 5 usecs of noise data (50*2 shorts)
• 36 2gb files were recorded. Most files contained 117 records (11700 ipps). This was 117 seconds of data (since each record was 1 second). Occasionally there was a shortened file.

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looking at the data:

• Power: 52 usecs (520 samples) of transmitter sample followed by 200 useconds (2000 samples) of no data (since the blanking interval was set to 200 usecs for the clutter).
• Clp:  500 usecs (5000 samples) of transmitter sample followed by 60 usecs (600 samples) of blanking.

The first plot shows the spectra of the clp height data (.ps)   (.pdf).

• 8192 sampled points (complex sampled at 10 Mhz) were used. 100 spectra were averaged.
• The echotek card was configured to only provide a 5 Mhz output bandwidth.

• Fig 1 top: This shows the power (black) and clp (red) tx samples for the I value. This is what the ipps should look like (except for the offset used for plotting). The gap  between 560 and 2600 in the power profile is from the IF blanking.  This starts at sample 5000 for the red (clp) data. The data comes from file.000 ipps 1600 and ipp 1800.
• Fig 1 bottom:  This had ipps 1699, 1700, and 1701. Ipp 1700 is a coded long pulse ipp. It should have been a power ipp (the program switched to clp on ipp 1800).   The dashed purple lines show the portion of the ipp that was used to compute the rms over each ipp. The clp ipps had tx samples (so the rms would be large) while the power ipp was blanked (so the rms should be small).
• Fig 2 top: This shows the rms computed over samples 1000 to 1500 for each ipp in file.000 . There are 11700 ipps in the file. The file started with power (where the rms was small). At ipp 1800 it switched to clp. The dashed red lines show single ipp glitches. In these cases the rms showed that the wrong kind of record was recorded.  The dashed green lines showed where the program transitions occurred. These were generated automatically using the algorithms described below.
• Fig 2 middle.. the glitches: To find the glitches, a 7 sample median filter was run across the 11700 ipps to create a median filtered array. Since the glitches were less than 4 ipps, they where not included in the filtered array. The filtered array was then subtracted from the initial data. This removed the program transitions and left the glitches. The result is plotted here. Anything that was greater than 30 a/d counts was considered a glitch. You can see 10 of them in this file. They occur about 100 ipps before a transition.
• Fig 2 bottom.. the program transitions: The rms was median filtered (7 points long). The derivative of the filtered data was then taken (shift by 1 and subtract). The absolute of this is  plotted.  Anything larger than 30 a/d counts is considered a program transition.
• Fig3 top.. glitch to next transition: The distance from a glitch to the next program transition was computed for every glitch in the 36 files (445 glitches). This distance was then plotted versus the cumulative ipp (for the 36 files). You can see that the glitches are drifting in time relative to when the program transitions occur. This means that the problem is not related to the program transition itself. The drifting is 200 ipps. This is the length of the two buffers that are used for input.
• Fig 3 2nd.. ipps per program transition: The ipps  for the program transitions are plotted modulo 1005.365 ipps vs the cumulative ipp. It shows that the  time for the power or clp fluctuated between 1005 and 1006 ipps. This is because the switching is done in software after the sps has run for 10 seconds and the ri has transferred all of the data to the vme computer.
• Fig 3 3rd.. ipps between glitches. This plots the cumulative ipp for each glitch modulo 100 ipps. You see that the ipp number (within 1..1000) remains constant for awhile and the jumps by 200 ipps. This corresponds to when the top plot has drifted through 200 ipps.
• Fig 4 bottom.. the glitches occur on the 1st ipp of each 1 sec rec: This plots the cumulative ipp for each glitch modulo 100 ipps. It is exactly zero. So the glitches occur at the start of the 1 second (100 ipp) records.

    There are some points that don't line up. The clipping levels were picked using the first file. If the levels changed a little, or a different glitch (rfi) occurred, then the algorithm could mess up. Around ipp 180000 it looks like the cycling of the programs (power, clp) was stopped for awhile (no glitches) and then restarted (or maybe the receiver was switched to load for awhile).
 

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