Bird Technologies 4527 - Manual (Page 13)

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Chapter 1 Introduction
Purpose and Function
The 43 is an insertion-type RF wattmeter, designed to measure RF power and
load match in 50 ohm coaxial transmission lines. It is intended for use with CW,
AM, FM, and TV modulation, but not pulse modulation. When used in 50 ohm
applications, the 43 has a maximum VSWR of 1.05 for frequencies up to 1000
MHz. The meter provides direct readings in watts with an expanded scale for
easy reading. The scale is graduated for 25, 50, and 100 full scale. Elements are
available in a variety of power and frequency ranges (see the Bird Electronic Cor-
poration Catalog for details).
This manual covers the operation of the Bird 43 Thruline Wattmeter and its
descendants. Two models have RF sampler ports, while the Bird 43P can mea-
sure peak power. The Bird 4520 series comes ready for panel mounting. Differ-
ences are discussed in Chapter 6, on page 27. Except where indicated,
instructions and specifications for the 43 apply to other models also.
Performance Characteristics and Capabilities
The Bird 43 is portable, with an attached 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 slotted screw on the lower front
face of the meter is used to zero the pointer. Below the meter face, the RF line
section protrudes slightly from the wattmeter housing with the element socket
in the center.
A shielded cable connects the RF line section to the rest of the wattmeter. This lets
you remove the line section from the wattmeter housing for custom installation and
still make measurements. The RF line section is precision machined to provide the
best possible impedance match to the transmission line under test. A formed phos-
phor-bronze spring finger protrudes into the element socket to make contact with
the element.
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 housing does
not interfere with connector changes.
To make measurements, a Bird Plug-In Element is inserted into the line section
socket and rotated against one of the stops. A small catch in the corner of the
socket face presses on the shoulder of the element to keep it in proper align-
ment. This assures good contact between the spring finger and the element con-
tact and between the lower edge of the element and the line section body (see
Figure 1).