430 tx Power meters
power meter for 430 tx power monitoring.
We have two ladybug Lb480A pulse power meters
upstairs (on for the dome and one for the ch).
It runs in power monitoring mode
- 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.
On 19aug11 project t2635 used a staggered ipp sequence followed by
codedlong pulse. The setup was:
The power monitor data was examined to see how the pulse power
- 9 stepped ipps (9600 ipps taken at each step). The sequence in
- Each ipp used a 52 usec rf pulse
- Since the rf pulse was fixed, the duty cycled changed with
- The sequence of 9 stepped ipps was followed by 20 seconds of
- ipp 10ms, rf pulse 440 usecs.
The plots show the pulse power
monitor measurements during the run (.ps) (.pdf):
- 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
- 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
- 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
- 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
- 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
- They are used to compute the duty cycle, and the average
- 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.
- 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
- 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.
- 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. &$
430 tx pulse monitoring: lb480A