Boonton 4240 RF Power Meter - Manual (Page 109)

Boonton 4240 Series RF Power Meter
6. Application Notes
in this section include pulse measurement fundamentals, automatic measurement
rinciples, and an analysis of measurement accuracy.
.1 Pulse Measurements
6.1.1 entals
The follo of power measurement fundamentals.
nmodulated Carrier Power. The average power of an unmodulated carrier consisting of a continuous, constant amplitude
alue of load impedance R, and applied voltage Vrms,
the average power is:
P = Vrms²/R
watts
Power meters designed to measure W power can use thermoelectric detectors which respond to the heating effect of the
de detectors which res nd to the voltage of the signal. With careful calibration accurate measurements can be
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 m
a thermoelectric detector, but the lack of sensitivity will limit the range. Diode
detectors can be used at low powe quare-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 i wo steps: (1) thermoelectric sensors measure the average signal power, (2) the reading
is then divided by the duty cycle to
tain pulse power, P pulse :
This section provides supplementary material to enhance your knowledge of the 4240 Series' advanced features and
measurement accuracy. Topics covered
p
6
Measurements Fundam
wing is a brief review
U
sinewave signal is also termed CW power. For a known v
C
signal or dio
obtained over po
eter with
r, s
.
n t
ob
P pulse = 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).
Application Notes
6-1