BIRD Thruline 43 User manual

INSTRUCTION BOOK
RF DIRECTIONAL
THRULINE® WATTMETER
MODEL 43
Also Covers Models 4431, 43P
And Series 4300, 4520
©Copyright 2008 by Bird Electronic Corporation
Instruction Book Part Number 920-43 Rev. H
Thruline® and Termaline® are registered trademarks
of Bird Electronic Corporation

i
Safety Precautions
The following are general safety precautions that are not necessarily
related to any specific part or procedure, and do not necessarily appear
elsewhere in this publication. These precautions must be thoroughly
understood and applied to all phases of operation and maintenance.
Keep Away From Live Circuits
Operating personnel must at all times observe general safety
precautions. Do not replace components or make adjustments to the
inside of the test equipment with the high voltage supply turned on.
To avoid casualties, always remove power.
Shock Hazard
Do not attempt to remove the RF transmission line while RF power is
present. Radiated RF power is a potential health hazard.
Do Not Service or Adjust Alone
Under no circumstances should any person reach into an enclosure to
service or adjust the equipment except in the presence of someone who
is capable of rendering aid.
Safety Earth Ground
An uninterruptible safety earth ground must be supplied from the
main power source to test instruments. Grounding one conductor of a
two conductor power cable is not sufficient protection. Serious injury
or death can occur if this grounding is not properly installed.
Resuscitation
Personnel working with or near high voltages should be familiar with
modern methods of resuscitation.

Bird Model 43 Wattmeter
ii
Safety Symbols
This symbol appears on the equipment indicating there is
important information in the instruction manual regarding
that particular area.
NOTE: Calls attention to supplemental information
Warning Statements
The following warnings appear in the text where there is danger to
operating and maintenance personnel, and are repeated here for
emphasis.
WARNING
Warning notes call attention to a procedure, which if not correctly
performed, could result in personal injury.
CAUTION
Caution notes call attention to a procedure, which if not correctly
performed, could result in damage to the instrument.
WARNING
Leaking RF energy is a potential health hazard. Never attempt to
connect or disconnect equipment from the transmission line while
RF power is being applied. Severe burns, electrical shock, or death
can occur.
WARNING
When working with RF powers of 200 watts or more, the potential of
the center conductor of the line section will be over 100 volts. Do not
touch the center conductor while RF power is on.

iii
Caution Statements
The following equipment cautions appear in the text whenever the
equipment is in danger of damage, and are repeated here for emphasis.
Safety Statements
USAGE
ANY USE OF THIS INSTRUMENT IN A MANNER NOT
SPECIFIED BY THE MANUFACTURER MAY IMPAIR
THE INSTRUMENT’S SAFETY PROTECTION.
USO
EL USO DE ESTE INSTRUMENTO DE MANERA NO
ESPECIFICADA POR EL FABRICANTE, PUEDE ANULAR LA
PROTECCIÓN DE SEGURIDAD DEL INSTRUMENTO.
CAUTION
For low reflection measurements, do not rotate the reflected power
element to read forward power. Damage to the element or
wattmeter could result.
CAUTION
Handle elements with care. Calibration could be disturbed if they
are dropped.
CAUTION
Do not attempt to remove the RF center conductor. This will
damage the line section.

Bird Model 43 Wattmeter
iv
BENUTZUNG
WIRD DAS GERÄT AUF ANDERE WEISE VERWENDET ALS VOM
HERSTELLER BESCHRIEBEN, KANN DIE GERÄTESICHERHEIT
BEEINTRÄCHTIGT WERDEN.
UTILISATION
TOUTE UTILISATION DE CET INSTRUMENT QUI N’EST PAS
EXPLICITEMENT PRÉVUE PAR LE FABRICANT PEUT
ENDOMMAGER LE DISPOSITIF DE PROTECTION DE
L’INSTRUMENT.
IMPIEGO
QUALORA QUESTO STRUMENTO VENISSE UTILIZZATO IN
MODO DIVERSO DA COME SPECIFICATO DAL PRODUTTORE
LA PROZIONE DI SICUREZZA POTREBBE VENIRNE
COMPROMESSA.
SERVICE
SERVICING INSTRUCTIONS ARE FOR USE BY
SERVICE - TRAINED PERSONNEL ONLY. TO AVOID
DANGEROUS ELECTRIC SHOCK, DO NOT PERFORM ANY
SERVICING UNLESS QUALIFIED TO DO SO.
SERVICIO
LAS INSTRUCCIONES DE SERVICIO SON PARA USO
EXCLUSIVO DEL PERSONAL DE SERVICIO CAPACITADO. PARA
EVITAR EL PELIGRO DE DESCARGAS ELÉCTRICAS, NO
REALICE NINGÚN SERVICIO A MENOS QUE ESTÉ
CAPACITADO PARA HACERIO.
WARTUNG

v
ANWEISUNGEN FÜR DIE WARTUNG DES GERÄTES GELTEN
NUR FÜR GESCHULTES FACHPERSONAL.
ZUR VERMEIDUNG GEFÄHRLICHE, ELEKTRISCHE SCHOCKS,
SIND WARTUNGSARBEITEN AUSSCHLIEßLICH VON
QUALIFIZIERTEM SERVICEPERSONAL DURCHZUFÜHREN.
ENTRENTIEN
L’EMPLOI DES INSTRUCTIONS D’ENTRETIEN DOIT ÊTRE
RÉSERVÉ AU PERSONNEL FORMÉ AUX OPÉRATIONS
D’ENTRETIEN. POUR PRÉVENIR UN CHOC ÉLECTRIQUE
DANGEREUX, NE PAS EFFECTUER D’ENTRETIEN SI L’ON N’A
PAS ÉTÉ QUALIFIÉ POUR CE FAIRE.
RF VOLTAGE MAY BE PRESENT IN RF ELEMENT
SOCKET - KEEP ELEMENT IN SOCKET DURING
OPERATION.
DE LA TENSION H.F. PEAT ÊTRE PRÉSENTE DANS LA PRISE
DE L’ÉLÉMENT H.F. - CONSERVER L’ÉLÉMENT DANS LA PRISE
LORS DE L’EMPLOI.
HF-SPANNUNG KANN IN DER HF-ELEMENT-BUCHSE
ANSTEHEN - ELEMENT WÄHREND DES BETRIEBS
EINGESTÖPSELT LASSEN.
PUEDE HABER VOLTAJE RF EN EL ENCHUFE DEL ELEMENTO
RF - MANTENGA EL ELEMENTO EN EL ENCHUFE DURANTE
LA OPERACION.
IL PORTAELEMENTO RF PUÒ PRESENTARE VOLTAGGIO RF -
TENERE L’ELEMENTO NELLA PRESA DURANTE IL
FUNZIONAMENTO.

Bird Model 43 Wattmeter
vi
About This Manual
This instruction book covers RF Directional Thruline Wattmeters
Models:
This instruction book is arranged so that essential safety information
appears in the front of the book. Reading the Safety Precautions
Section before operating the equipment is strongly advised.
The remainder of this Instruction Book is divided into Chapters and
Sections. At the beginning of each chapter, a general overview
describes the contents of that chapter.
Operation
First time users should read Chapter 1 - Introduction, Chapter 3 -
Installation, and Chapter 2 - Theory of Operation, to get an overview
of equipment capabilities and installation. Specifications are provided
in Chapter 7 - Specifications. An experienced operator can refer to
Chapter 4 - Operating Instructions. All instructions necessary to
operate the equipment appears in this chapter. If you are not using
the Model 43, refer to Chapter 6 - Model Differences for instructions
specific to your unit.
Maintenance
All personnel should be familiar with the preventive maintenance
found in Chapter 5 - Maintenance. If a failure should occur, the
troubleshooting section will aid in isolating and correcting the cause.
43 43P 4301 4305A 4431
4521 4522 4523 4525 4526 4527

vii
Changes to This Manual
We have made every effort to ensure this manual is accurate. If you
should discover any errors or if you have suggestions for improving
this manual, please send your comment to our factory. This manual
may be periodically updated. When inquiring about updates to this
manual refer to the part number and revision level on the title page.

Table of Contents
Safety Precautions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i
About This Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Purpose and Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Performance Characteristics and Capabilities. . . . . . . . . . . . . . . . . .1
Theory of Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Travelling Wave Viewpoint. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Coupling Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Load Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Standing Wave vs. Travelling Wave Viewpoint . . . . . . . . . . . . . . . . .8
ρvs. φ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Low Reflection Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Transmitter Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Component Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Frequency Response. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
Impedance Mismatch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
Connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
Remote Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
Operating Instructions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Normal Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Load Matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
Cleaning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
Contact Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
Zero Adjust. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
Customer Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Bird 43 Replacement Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
Available “QC” Type Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . .33
Model Differences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Bird 43P Peak Wattmeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Peak Detector Response. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Rectangular Pulses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
Peak Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
Bird 4301 Thruline Wattmeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
Bird 4305A Thruline Wattmeter . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
Bird 4305A Replacement Parts List. . . . . . . . . . . . . . . . . . . . . .39
Bird 4431 Thruline Wattmeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Bird 4431 Replacement Parts List. . . . . . . . . . . . . . . . . . . . . . .42
Bird 4520 Series Thruline Wattmeters. . . . . . . . . . . . . . . . . . . . . . .43
Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
Bird 4520 Series Replacement Parts List . . . . . . . . . . . . . . . . .43
Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45

1
Chapter 1 Introduction
Purpose and Function
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 measure peak power. The Bird 4520 series comes ready
for panel mounting. Differences are discussed in Chapter 6, on
page 35. Except where indicated, instructions and specifications for
the 43 apply to other models also.
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 Corporation Catalog for details).
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.

Bird Model 43 Wattmeter
2
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
phosphor-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 alignment. This assures good contact between the
spring finger and the element contact and between the lower edge of
the element and the line section body (see Figure 1).
Contacts on opposite sides of the element connect with the spring
finger when the element is in the forward or reverse position. This
occurs when the stop pin on the element is against either stop and the
catch is in place.
Figure 1
Securing an
element

3
Figure 2
Bird 43 Thruline Wattmeter
Outline Drawing

Bird Model 43 Wattmeter
4

5
Chapter 2 Theory of Operation
Travelling Wave Viewpoint
The easiest way to visualize Thruline operation is from a travelling
wave viewpoint. In transmission lines the voltages, currents, standing
waves, etc., on any uniform line section result from the interaction of
two travelling waves:
yThe forward wave (and its power) travels from the source to the
load. It has RF voltage Efand current Ifin phase, with Ef/ If= Zo.
yThe reflected wave (and its power) originates by reflection at the
load and travels from the load back to the source. It has an RF
voltage Erand current Irin phase, with Er/ Ir= Zo.
Each wave is mathematically simple and has a constant power:
Wf= Watts Forward = Ef2/ Zo= If2Zo= EfIf
Wr= Watts Reflected = Er2/ Zo= Ir2Zo= ErIr
Zois the characteristic impedance of a uniform line section. For useful
lines it is usually a pure resistance of 50 ohms. The RF circuit of the
Bird 43 is a length of uniform air line with Zo= 50 ohms.

Bird Model 43 Wattmeter
6
Coupling Circuit
The coupling circuit that samples the travelling waves is in the Bird
Plug-In Element. The element circuitry and its relationship to the rest
of the Bird 43 are illustrated in Figure 3.
Current is produced in the coupling circuit by the travelling waves in
the line section. Both inductive and capacitive coupling contribute to
this. The inductive current flows in the direction of the travelling
wave. The capacitive current is independent of the direction of the
travelling wave. Therefore, the inductive current produced by one of
the travelling waves will add in phase with the corresponding
Figure 3
Thruline Wattmeter Schematic

Theory of Operation
7
capacitive current, while that produced by the wave travelling in the
opposite direction will subtract. The additive or “arrow” direction is
assigned to the forward wave.
The electrical characteristics of the element are carefully adjusted so
that, for the reverse travelling wave, the inductive current will
completely cancel the capacitive current. The result is directivity
greater than 25 dB. Thus, the element is sensitive at either of its
settings, but to only one of the two travelling waves. Thruline
Wattmeter measurements are also independent of position along the
transmission line.
Like similar diode devices, the Bird 43 indicates the carrier component
of amplitude modulation, with very little response to side band
components added by modulation.
Load Power
For loads with a VSWR of 1.2 or less, the power dissipated in a load
(Wl) is equivalent (with less than one percent error) to the forward
power (Wf). When appreciable power is reflected, as with an antenna,
it is necessary to use the exact load power which is given by:
Wl= Watts into Load = Wf– Wr
Good load resistors, such as Bird Termaline loads, will give negligible
reflected power.

Bird Model 43 Wattmeter
8
Standing Wave vs. Travelling Wave Viewpoint
As mentioned previously, the Thruline Wattmeter reacts to forward
and reverse travelling waves to measure power in a transmission line.
The standing wave viewpoint, also widely used, is highly developed
both in theory and in practice. This viewpoint can be traced to the
early use of slotted transmission lines.
The slotted line measures the standing wave ratio by mechanically
positioning a voltage detector at peaks and nulls along a length of line
section. Its drawbacks are that it is usually too long, too expensive for
good accuracy, not portable, and too slow. These problems grow rapidly
as the measurement frequency drops below 1000 MHz. The Thruline
Wattmeter by comparison is fast, convenient, and accurate. It provides
the same information as a slotted line with the exception of the phase
angle of the reflection coefficient (distance, load to minimum).
ρvs. φ
The simple relationships:
can be used to convert between the standing wave ratio (ρ) and the
reflected/forward power ratio (φ), which can be directly read from the
Thruline Wattmeter. The relationship between ρand φis graphed in
Figure 4 and Figure 5.
and
Where ρ= VSWR
and φ= Wr/ Wf
ρ1+ φ
1φ–
----------------=
φρ1–
ρ1+
------------=2

Theory of Operation
9
NOTE: Attenuation, measured in dB, can be derived from the
power ratio by the equation Ndb = 10 log φ.
VSWR scales and their attendant controls for setting the reference
point have been intentionally omitted from the Bird 43. Experience
using the Thruline Wattmeter for transmitter tune-up, antenna
matching, etc. will show that the power ratio measurement is as
useful in practice as the standing wave ratio.
A trial is suggested – forget about VSWR for a few days and think
in terms of φ= Wr/ Wf. The two meter readings, Wrand Wf, give
a useful, approximate picture of the results without bothering to
calculate the power ratio exactly. Consider that, for an antenna
matching problem, the main objective usually is to minimize Wr.
Anything done experimentally to this end will be seen when the
element is turned to the reflected power position.

Bird Model 43 Wattmeter
10
Figure 4
Percent Reflected Power vs. VSWR (1.0 – 1.3)