Boonton 4530 Peak Power Meter User Manual - Manual (Page 146)

Chapter 5 Boonton Electronics
Making Measurements 4530 Series RF Power Meter
5-4
CW mode measures the average power of CW signals (and modulated signals if using a thermal sensor or
diode sensor within the square-law region), and displays a high-resolution measurement. The power is
automatically corrected for sensor frequency response, and filtered using user-selectable parameters, then
displayed on the front panel readout. The display format, scaling, units (both linear and logarithmic) and
resolution are programmable. Two auxiliary measurements can be shown: the minimum and maximum held
power (after filtering).
The measurement may also be presented in a graphical format showing power (or voltage) versus time. The
display can span from one second to one hour, and in the slower time settings, it goes into roll mode, which
presents a chart-recorder type scrolling trace. This can be very useful for observing a drifting signal.
The primary display may be the actual sensor signal amplitude, offset amplitude, or a mathematical function
(ratio, sum or difference) of the sensor signal and the signal from a second sensor or stored reference.
5.3.2 Modulated Mode . Modulated mode operates only with peak power sensors. In this mode, the instrument
measures the average, instantaneous peak and instantaneous minimum power of a modulated RF signal. One
or more of these measurements can be displayed on the screen in a text or graphical format.
The processed sensor signal is continuously sampled and digitized by a high-speed A/D converter. Each A/
D sample is linearized to convert to a power reading, then adjusted for gain offset and sensor frequency factor.
The running average of these readings is calculated to yield the average modulated power. Additionally, each
sample is checked for a new instantaneous minimum or peak. Every time a new peak occurs, it replaces the
previous value. These values may be held to show the highest and lowest instantaneous power that has
occurred since measurement started, or may be automatically decayed after a preset time interval so the
current peak-to-average power may be viewed. This is especially convenient if the overall signal level is
changing. Held minimum and maximum average (filtered) power may also be displayed.
In most ways, Modulated Mode is similar to CW mode. The display can show the sensor signal level or a math
function, and displays a power-versus-time trace in graph mode, and text mode allows a full choice of display
formats. The primary difference is that the minimum and maximum power measurements include the lowest
and highest instantaneous readings, while in CW mode, only the lowest and highest filtered readings may be
displayed.
5.3.3 Statistical Mode . Statistical Mode operates only with peak power sensors, and is used to provide a
statistical analysis of the distribution of power over a period of time. By acquiring a very large number of
power samples, it is possible to determine, with a high degree of confidence, the statistical probability that the
power will fall within a specific range. This technique is very helpful for digitally modulated signals for
observing amplifier linearity with real signals, and predicting compression and bit error rate.
The processed sensor signal is continuously sampled and digitized by the high-speed A/D, and the number
of times each A/D code occurs is counted. In this fashion, a high-resolution histogram is formed which can
be processed to yield a CDF (cumulative distribution function), CCDF (the complement to the CDF, also know
as 1-CDF) or a conventional bar-type histogram with each bar showing the probability that the power will fall
within a certain range.
These functions can be displayed in graphical format, and screen cursors can be moved to specific probabili-
ties or power levels on the curve, and the corresponding value read at that point. The text display can show
the cumulative average power, or a tabular display that adds a number of other measurements including the
highest and lowest power points during the entire interval. Note that in graph mode, the displayed trace is
power versus percent probability, while all the other 4530 measurement modes show power versus time. If the
instrument is in mixed mode (one channel is in Statistical Mode, and the other is in Modulated Mode or CW
Mode), two completely separate unit systems are presented on the X-axis of the graph display.