MM0474
LESSON 2.
POWER MEASUREMENTS EQUIPMENT, PART I
AIPD Subcourse Number MM0474................. Power Measurements
Lesson Objective ............................. After studying this
lesson
you
should be able to:
1. State
the
purpose,
characteristics, concepts and
operation of bolometers.
2. Describe
the
purpose,
characteristics,
operation,
block
diagram
and
circuit
analysis of power meters and
thermistor mounts.
Credit Hours ................................. Four
TEXT
1.
INTRODUCTION.
a. The basic concept of power is the same for microwave as for low
frequencies; however, the practical aspects of the two are quite different.
For instance, in most circuits, power can be specified and measured in terms of
voltage across the circuit and the current flowing through the circuit as a
result of such voltage. In microwave, such voltage and current can neither be
simply specified, nor can they ordinarily be measured.
In microwave, power
measurements are often made in the milliwatt region by the bolometric method.
In the higher power measurements, the calorimetric methods are used.
These
concepts find wide application in measurements of attenuation, transmission
losses, and other related subjects.
b. The calibrator must have a knowledge of the type of meters used for
power measurements. During this lesson we will cover the model 431C and 432A
power meters to include the thermistor mounts used with them.
2.
MODEL 431C POWER METER.
a. Description.
(1) The Model 431C Power Meter (Figure 1), with temperature-compensated
thermistor mounts, measures RF power from 10 microwatts (-20 dBm) to 10
milliwatts (+10 dBm) full scale in the 10 MHz to 40 GHz frequency range.
Direct reading accuracy of the instrument is 1% of
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