Boonton 4530 Peak Power Meter User Manual - Manual (Page 147)

Boonton Electronics Chapter 5
4530 Series RF Power Meter Making Measurements
5-5
Although the sample rate in statistical mode is high enough to gather a large sample population in a very short
time (over one million power samples are recorded each second), the strength of this mode is that it can be
allowed to run for a long period of time to capture very infrequent events. The sample counters are 32 bits, so
the runtime for a single CDF can be programmed to be more than an hour. For continuous running processes,
the CDF can be programmed to automatically restart or to decimate the sample counters when a programmed
count is reached.
Although statistical mode can display the average, minimun and peak power, it is important to note that these
are all cumulative results that take into account the entire sample history since the run was started. If the
power level or other signal characteristic is changed, the run should be cleared and restarted by pressing
ESC/Stop twice (once to stop, again to clear), then pressing Enter/Run to start acquiring a fresh data set.
5.3.4 Pulse Mode . For periodic or pulsed signals, it is often necessary to analyze the power for a portion of the
waveform, or a certain region of a pulse or pulse burst. For these applications, the 4530 Series has a triggered
Pulse Mode. Operation in this mode is similar to a digital storage oscilloscope - power samples are stored in
a circular memory buffer until a trigger signal is received. The samples, with the desired relationship to the
trigger signal, are then selected and processed to obtain a power-versus-time trace.
The trigger signal can be either internal, triggered from a rising or falling edge on the measured signal; or
external, triggered from a rear-panel BNC input. The trigger level and polarity are both programmable, as is the
trigger delay time and trigger holdoff time. Displays of both pre- and post-trigger data are available, and an
auto-trigger mode can be used to keep the trace running when no trigger edges are detected. A “peak-to-
peak” trigger level setting can be chosen to automatically set the trigger level based on the currenly applied
signal. The time span of the graph display can be selected from 2.5 microseconds to 5 seconds. This would
be equivalent to the 250nS/div to 500ms/div timebase settings on an oscilloscope, since a typical scope
screen has 10 horizontal divisions. The 4530 has no visible graticule, however, so horizontal sensitivity is set
as the timespan, which is the time interval spanned by the visible trace window.
Programmable time markers can be moved to any portion of the trace that is visible on the screen, and these
can be used to mark regions of interest for detailed power analysis. The instrument can display power at each
marker, as well as average, minimun and maximum power in the region between the two markers. This is very
useful for examining the power during a TDMA or GSM burst when only the modulated portion in the center
region of a timeslot is of interest. By adjusting trigger delay and other parameters, it is possible to measure the
power of specific timeslots within the burst. Trigger holdoff allows burst synchronization even if there is more
than one edge in the burst which may satisfy the trigger level. Simply set the holdoff time to slighly shorter
than the burst’s repetition interval to guarantee that triggering occurs at the same point in the burst each
sweep.
Pulse Mode is unlike the other operating modes of the 4530 in that it is discontinuous. For each sweep, data
acquisition into the circular buffer is restarted, and it runs at high speed until a trigger edge has been detected
and all post-trigger samples acquired. At this point, acquisition stops, and the buffer is processed and
displayed before another trace is restarted. Because the 4530’s trigger system and peak sensor sampling
system are common to both channels, it is not possible to run one channel in Pulse Mode while the other is in
Statistical or Modulated mode. The burst and continuous sampling processes can not be operated simulta-
neously. No such limitations exist if the second channel is in CW mode, and it is perfectly acceptable to run
one channel in Pulse Mode and the other in CW mode. Note, however, that in this case the CW sensor
bandwidth is not nearly high enough to display signal amplitude changes at most timespan settings, and it is
not possible to use a CW sensor as a trigger source.
For periodic waveforms, automatic measurement of waveform parameters is available in pulse mode. When-
ever a stable, periodic signal is detected, the 4530 will automatically calculate a number of pulse parameters
such as pulse frequency, width, duty-cycle, rise and fall times, top and bottom powers, pulse on power,
overshoot, and average power over one full cycle. These measurements can be viewed on secondary pages
of the single-channel text display. For added flexibility, certain time and power thresholds used to define start
and end of pulse transitions are user-programmable.