Boonton 4541, Instruction Manual

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Boonton 4540 Series RF Power Meter
Getting Started
3-17
3.6 Making Measurements
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 modulation and its bandwidth. Note that power
sensors respond only to the amplitude modulation component of the modulation, and constant envelope modulation types
such as FM can be considered a CW carrier for power measurement purposes.
3.6.1 Modulated Mode
Modulated Mode is best for measuring repetitive signals. Since this mode performs a continuous measurement, it does not
differentiate between the times a pulsed or periodic signal is off, and the times it is on. If you wish to make measurements
that are synchronous with a period of a waveform, consider using Pulse Mode instead.
Modulated Mode is the best for the following types of measurement:
• Moderate signal level (above -40dBm for Peak sensors and -60dBm for CW sensors)
• Signal that is continuously modulated with a modulation band width that is less than 20 MHz.
• Signal modulation may be periodic, but only non synchronous measurements are needed (overall average and peak
power).
• Noise-like digitally modulated signals such as CDMA and OFDM when only average measurements are needed.
The measured result is the average power of the signal. Since the graphic display would basically just show a straight line,
measurements in Modulated Mode are best viewed using the Text Display Mode.
Figure 3-6 shows a two channel measurement displaying an average power in modulated mode.
Figure 3-6 Modulated Mode Text Display
Menu Instructions:
1. To set the 4540 into Modulated Mode, select
Measure > Mode > Modulated.
2. To set the text display mode, press the
Graph/Text
function key.