power meter for 430 tx power monitoring.

• power meter with 100MHz to 8Ghz response
• 10 MHz video bandwidth
• 2 usec sampling .
• 125 samples per buffer.
• 2000 buffers sent to cpu before pulse profile info computed.
  

• 9 stepped ipps (9600 ipps taken at each step). The sequence in usecs:
  
• 1040,1144,1248,1352,1456,1560,1664,1768,1872.
• Each ipp used a 52 usec rf pulse
• Since the rf pulse was fixed, the duty cycled changed with each step.
  
• The sequence of 9 stepped ipps was followed by 20 seconds of codedlong pulse:
• ipp 10ms, rf pulse 440 usecs.
  

• Page 1: results for run:
  
• top: Peak power (black) and pulse power(red).
• middle: average power
• bottom: duty cycle of rf pulse.
• Page 2: Blowup of 3 cycles of  peak,pulse,average power an duty cycle
• Page 3: Measure how long it took to do things:
• Top: peak power
• the X axis uses the time stamps written to the power meter logfile
• The dashed red lines are the computed length of time each ipp step should have taken.
• Middle: the duty cycle:
• The long noisy 20 sec duration was the coded long pulse (20 to 40 secs), then the ipp steps began (at 40 seconds).
• Bottom: the time step between samples returned by the power meter.

Discussion:

• The power meter setup:
• 430 MHz
• 13 db defined pulse
• 2000 averages (buffers) are requested.
• The .5 MHz sampling of the 10MHz video IF is done.
• A  buffer of 125 samples is acquired and then sent to the pc.
• It is sampled at 2 usecs. So one buffer takes 256 usecs.
  
• There are actually 2 samplers: one  looking at the signal and a second looking with a pad in front of it so the system can covert the -60dbm to 20 dbm range.
• after 2000 buffers (512 milliseconds) the pulse info is computed:
• the sampled data are sorted by amplitude
• The first point is the peak power.
  
• We've set the pulse threshold to 13 db so the program searches for the 1st point 13 db below the peak (or first point). All points from here to the start are in the pulse.
• The average of these points is the pulse power.
• All points from the 13db point to the end are out of the pulse.
• They are used to compute the duty cycle, and the average power.
  
• Looking at the time between samples (bottom plot):
• It always took .6 seconds independent of the number of ipps in .6 seconds.
• The difference  between the sampling time (512 ms) and the measured time (600 ms) is the overhead.
• overhead is about 20%.
• To increase the signal to noise we should probably switch the filter to 2 MHz. This would not affect the pulse too much and it would increase the signal to noise.
• There is a 2nd mode called pulse profiling mode. It uses interleaved under sampling:.
• the user specifies the number of points in a sweep (say 10000).
• The routine taken 10000/128 buffers of data
• After each buffer the device increments the a/d clock freq by 20 ns. This allows for the interleaved sampling.
  

Notes:

• Data from the various experiments is stored at: /share/aserv00/pwrmet
  
• Data is normally transferred from the pc in the control room (tx430)  using  cygwin on the windows pc.
  
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Documentation:

    430 tx pulse monitoring: lb480A

• lb480A data sheet
• lb480A programming guide 2.1 (.pdf)
• lb480A programming guide for pulse profile (.pdf)
  
• lb480a product manual (68 pages) (.pdf)
• lb480a quick start guide (32 pages) (.pdf)
• My notes on the manuals (.txt)

Misc.

• Luis's calibraton measurements 08feb12(.pdf)
  

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