Boonton 4530 Peak Power Meter User Manual - Manual (Page 149)

Boonton Electronics Chapter 5
4530 Series RF Power Meter Making Measurements
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5.4.4 Statistical Mode . Statistical Mode is only available when using a peak power sensor, and is best choice for
analyzing “noise-like” signals that are modulated in a random, nonperiodic fashion. Statistical mode yields
information about the probability of occurance of various power levels without regard for when those power
levels occured. Many digitally modulated spread-spectrum formats use a bandwidth coding techniques or
many individual modulated carriers to distribute a source’s digital information over a wide bandwidth, and
temporally spread the data for improved robustness against interference. When these techniques are used,
it is difficult to predict when peak signal levels will occur. Analysis of millions of data points gathered during
a sustained measurement of several seconds or more can yield the statistical probabilities of each signal level
with a high degree of confidence. Statistical Mode is best of the following types of measurements:
• Moderate signal level (above about -40dBm except when modulation is “off”).
• “Noise-like” digitally modulated signals such as CDMA (and all its extensions) or COFDM when probabil-
ity information is helpful in analyzing the signal.
• Any signal with random, infrequent peaks, when you need to know just how infrequent those peaks are.
5.5 SETTING MEASUREMENT PARAMETERS
Once a sensor and measurement mode have been chosen, it is often possible to begin making very basic measurements
simply by using the power meter’s default menu settings. In most cases, however, better results are available by
customizing the measurement parameters to match your specific signal. The following list gives some guidelines for
how to best configure the 4530 for specific types of measurements, but remember that there is no substitute for
understanding the characteristics of the signal that you are trying to measure. Most of these items are not required
settings, and many are not applicable to all measurement modes, but consider setting each of these items when setting
up the meter for any type of measurement.
5.5.1 What You Need To Know. To perform accurate measurements, the following is a minimum list of things
you should know about the signal that you wish to measure.
Signal frequency - The center frequency of the carrier must be known to allow sensor frequency response
compensation.
Modulation Bandwidth - If the signal is modulated, know the type of modulatation and its bandwidth. Note
that power sensors respond only to the the amplitude modulation component of the modulation, and con-
stant envelope modulation types such as FM can be considered a CW carrier for power measurement pur-
poses.
Modulation Timing - If the modulation is periodic, know the pulse repetition rate, frame rate, and any other
relavant timing information. This is not important unless you intend to perform synchronous (triggered)
measurements in Pulse Mode.
5.5.2 Channel Parameters Menu Settings
Frequency (Required setting for all modes) - Setting the frequency tells the power meter what frequency RF
signal is being applied to the power sensor. This frequency is used to automatically apply a calibration factor
to compensate for the sensor’s frequency response deviations.
Offset (Optional setting for all modes) - Inform the power meter of a global gain offset to scale the reading.
Used to compensate for attenuators, couplers or amplifiers in the signal chain.
Filter (Optional setting for CW and Modulated mode) - Sets the signal integration filter to a user-defined
value to reduce measurement noise. The normal setting is “Auto”, but setting a manual filter allows user
control of the tradeoff between measurement noise and settling time.