Application Notes
This section provides supplementary material to enhance your knowledge of the RFM3000 operation, advanced fea-
tures, and measurement accuracy. Topics covered in this section include pulse measurement fundamentals, automatic
measurement principles, and an analysis of measurement accuracy.
5.1 Introduction to Pulse Measurements
5.1.1 Measurement Fundamentals
The following is a brief reaview of the power measurement fundamentals.
Unmodulated Carrier Power
The average power of an unmodulated carrier consisting of a continuous, constant amplitude sinewave signal is also
termed continuous wave (CW) power. For a known value of load impedance R, and applied voltage
𝑉
𝑟𝑚𝑠
, the average
power is:
𝑃 =
𝑉
𝑟𝑚𝑠
2
𝑅
𝑤𝑎𝑡𝑡𝑠
Power meters designed to measure CW power can use thermoelectric-based sensors 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
. 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,
𝑃
𝑝𝑢𝑙𝑠𝑒
:
𝑃
𝑝𝑢𝑙𝑠𝑒
=
𝐴𝑣𝑒𝑟𝑎𝑔𝑒 𝑃 𝑜𝑤𝑒𝑟
𝐷𝑢𝑡𝑦 𝐶𝑦𝑐𝑙𝑒
Where Duty Cycle:
𝐷𝑢𝑡𝑦 𝐶𝑦𝑐𝑙𝑒 =
𝑃 𝑢𝑙𝑠𝑒 𝑊 𝑖𝑑𝑡ℎ
𝑃 𝑢𝑙𝑠𝑒 𝑃 𝑒𝑟𝑖𝑜𝑑
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
).
Summary of Contents for RFM3000 Series
Page 1: ......