Bird Technologies 4304A - Manual (Page 12)

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Chapter 1 Introduction
Purpose and Function
The Bird 4304A Wattmeter is an in-line sensor that measures RF power and load
match in 50
Ω coaxial transmission lines. It can be used with CW, AM, FM, and TV
modulation, but not pulse modulation. It is supplied with a special broadband
element with a frequency range of 25 to 1000 MHz. It can measure up to 500 W,
depending on the frequency, and has a maximum VSWR of 1.07 with the stan-
dard “N” connectors. A range switch allows the full scale power to be reduced
for greater accuracy.
The wattmeter is portable, with an included carrying strap. It has an aluminum
housing and an easily removed back cover, with bumpers on the base and back
that allow the meter to stand or lie flat. For additional protection, the
microammeter is specially shock mounted. A screw on the lower front face of the
meter is used to zero the pointer. Below the meter face, the RF line section pro-
trudes slightly from the wattmeter housing with the element socket in the center.
The RF line section is precision machined to provide the best possible imped-
ance match to the transmission line under test. A formed phosphor-bronze
spring finger protrudes into the element socket to make contact with the ele-
ment. At each end of the line section are Bird Quick-Change RF connectors that
may be interchanged with any other Bird “QC” connector. The wattmeter hous-
ing does not interfere with connector changes.
Combining the Thruline Wattmeter with a Bird Termaline Load Resistor creates
an accurate absorption wattmeter. With this combination, readings only need to
be taken in the forward direction because the reflected power will be negligible.
Figure 1 Bird 4304A Thruline Wattmeter Outline Drawing
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15
50
150
500
6-7/8”
(175 mm)
4”
(100 mm)
2-3/8”
(59 mm)
“QC” CONNECTORS
FEMALE N NORMALLY
SUPPLIED
4”
(100 mm)
1-3/4”
(44 mm)
POWER RANGE
SWITCH
ELEMENT