Application notes, 1 pulse measurements, 1 measurements fundamentals – Boonton 4540 Peak Power Meter User Manual User Manual
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Boonton 4540 Series RF Power Meter
Application Notes
6-1
6. Application Notes
This section provides supplementary material to enhance your knowledge of the 4540 Series' advanced features and
measurement accuracy. Topics covered in this section include pulse measurement fundamentals, automatic measurement
principles, and an analysis of measurement accuracy.
6.1 Pulse Measurements
6.1.1 Measurements Fundamentals
The following is a brief review of power measurement fundamentals.
Unmodulated Carrier Power. The average power of an unmodulated carrier consisting of a continuous, constant amplitude
sinewave signal is also termed CW power. For a known value of load impedance R, and applied voltage Vrms,
the average power is:
P = Vrms²/R
watts
Power meters designed to measure CW power can use thermoelectric detectors which respond to the heating effect of the
signal or diode detectors which respond to the voltage of the signal. With careful calibration accurate measurements can be
obtained over a wide range of input power levels.
Modulated Carrier Power. The average power of a modulated carrier which has varying amplitude can be measured
accurately by a CW type power meter with a thermoelectric detector, but the lack of sensitivity will limit the range. Diode
detectors can be used at low power, square-law response levels. At higher power levels the diode responds in a more linear
manner and significant error results.
Pulse Power. Pulse power refers to power measured during the on time of pulsed RF signals (Figure 6-1). Traditionally,
these signals have been measured in two steps: (1) thermoelectric sensors measure the average signal power, (2) the reading
is then divided by the duty cycle to obtain pulse power,
Ppuls
e:
Ppulse
= Average Power/ Duty Cycle (measured)
where Duty Cycle = Pulse Width/Pulse Period
Pulse power provides useful results when applied to rectangular pulses, but is inaccurate for pulse shapes that include
distortions, such as overshoot or droop
(Figure 6-2).