BIRD Thruline 4304A User manual

RF Directional
Thruline® Wattmeter
MODEL 4304A
Operation Manual
©Copyright 2016 by Bird Technologies, Inc.
Instruction Book Part Number 920-4304A Rev. F
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 apply to all
phases of operation and maintenance.
WARNING
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.
WARNING
Shock Hazard
Do not attempt to remove the RF transmission line while RF power is present.
WARNING
Do Not Service Or Adjust Alone
Under no circumstances should any person reach into an enclosure for the
purpose of service or adjustment of equipment except in the presence of
someone who is capable of rendering aid.
WARNING
Safety Earth Ground
An uninterruptible earth safety 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 supplied.
WARNING
Resuscitation
Personnel working with or near high voltages should be familiar with modern
methods of resuscitation.
WARNING
Remove Power
Observe general safety precautions. Do not open the instrument with the
power on.

Safety Precautions
ii
Safety Symbols
The caution 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 safety warnings appear in the text where there is danger to
operating and maintenance personnel, and are repeated here for emphasis.
Caution Statements
The following equipment cautions appear in the text whenever the equipment is
in danger of damage, 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
Never attempt to connect or disconnect equipment RF equipment from the
transmission line while RF power is being applied.
Leaking RF energy is a potential health hazard.
WARNING
When working with RF powers of 200 watts or more, the potential of the
center conductor of the line section will exceed 100 volts.
Do not touch the center conductor while RF power is on.
CAUTION
Do not drop. Calibration could be disturbed or the meter could be damaged
as a result.

RF Directional Thruline® Wattmeter 4304A
iii
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.
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
CAUTION
Above 800 MHz, do not exceed 150 W RF power.
CAUTION
RF power must not exceed range switch setting.
CAUTION
Do not attempt to remove the RF center conductor. This will damage the line
section.
CAUTION
When handling the circuit board, use caution:
Do not bend the DC contact finger that extends into the line section.
Do not lose the contact finger insulator or the
spacers on the mounting screws.
Do not disturb the potentiometer settings.

Safety Precautions
iv
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.

RF Directional Thruline® Wattmeter 4304A
v
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
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.
ASSISTENZA TECNICA
LE ISTRUZIONI RELATIVE ALL’ASSISTENZA SONO PREVISTE
ESCLUSIVAMENTE PER IL PERSONALE OPPORTUNAMENTE
ADDESTRATO. PER EVITARE PERICOLOSE SCOSSE
ELETTRICHE NON EFFETTUARRE ALCUNA RIPARAZIONE A
MENO CHE QUALIFICATI A FARLA.

Safety Precautions
vi
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.

RF Directional Thruline® Wattmeter 4304A
vii
About This Manual
This manual covers the operating and maintenance instructions for the
following models:
Changes to this Manual
We have made every effort to ensure this manual is accurate. If you discover
any errors, or if you have suggestions for improving this manual, please send
your comments to our Solon, Ohio factory. This manual may be periodically
updated. When inquiring about updates to this manual refer to the part number
and revision on the title page.
Literature Contents
Chapter Layout
Introduction — Describes the features of the 43 Wattmeter, lists equipment
supplied and optional equipment, and provides power-up instructions.
Theory of Operation — Describes how the 43 Wattmeter works and
Installation — Describes how to set up and prepare the 43 Wattmeter for use.
Operation — All instructions necessary to operate the equipment appears in
this chapter.
Maintenance — Lists routine maintenance tasks as well as troubleshooting
for common problems.
Model Differences — Describes how each individual models vary from each
other.
Specifications — Specifications and parts information are included in this
chapter.
43 43P 4301 4305A 4431 4527
4521 4522 4526

viii
Table of Contents
Safety Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i
Safety Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Warning Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Caution Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Safety Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
About This Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Changes to this Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Chapter Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Chapter 2 Theory of Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Traveling Wave Viewpoint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Coupling Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Load Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Standing Wave vs. Traveling Wave Viewpoint . . . . . . . . . . . . . . . . . . . . . . . . 4
vs.  
Component Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Impedance Mismatch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Chapter 3 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Load Matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Chapter 4 Operating Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Normal Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Low Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
VSWR Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Chapter 5 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Zero Adjust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Connector Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Element Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Back Cover Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Line Section Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Meter Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

RF Directional Thruline® Wattmeter 4304A
ix
Calibration Checks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Setup Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Calibrating a Bird Element 4304A-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Customer Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Replacement Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Available “QC” Type Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Limited Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

1
Chapter 1 Introduction
Purpose and Function
The Bird 4304A Wattmeter is an in-line sensor that measures RF power and load
match in 50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 standard “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
protrudes slightly from the wattmeter housing with the element socket in the
center.
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.
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

2
Chapter 2 Theory of Operation
Traveling 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:
The forward wave (and its power) travels from the source to the load.
It has RF voltage Efand current Ifin phase, with Ef/ If= Zo.
The 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 Er
and current Irin phase, with Er/ Ir= Zo.
Each wave is mathematically simple and has a constant power:
Note: Zois the characteristic impedance of a uniform line section.
For useful lines it is usually a pure resistance of 50. The RF circuit
of the Bird 43 is a length of uniform air line with Zo= 50.
WfWattsForward E f
2Zo
If
2ZoEfIf
====
WrWatssReflected Er
2Zo
Ir
2ZoErIr
====

Theory of Operation
3
Coupling Circuit
Figure 2 Thruline Wattmeter Schematic
The element, which contains the coupling circuit, and its relationship to the rest of the
Bird 4304A is shown in Figure 2 . Current is produced in the coupling circuit by traveling
waves in the line section, through both inductive and capacitive coupling. The inductive
current flows in the direction of the traveling wave, while the capacitive current is
independent of the direction of the wave. Therefore, the inductive current produced by
one traveling wave will add in phase with the corresponding capacitive current, while
that produced by the wave traveling 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 wave, the inductive current will completely cancel the capacitive current, giving
a directivity greater than 20 dB. Thus, the element is sensitive at either of its settings,
but to only one of the two traveling waves. Thruline Wattmeter measurements are also
independent of position along the transmission line.
Like similar diode devices, the Bird 4304A indicates the carrier component of
amplitude modulation, with very little response to side band components
added by modulation.

RF Directional Thruline® Wattmeter 4304A
4
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:
Good load resistors, such as Bird Termaline loads, will give negligible reflected
power.
Standing Wave vs. Traveling Wave Viewpoint
As mentioned previously, the Thruline Wattmeter reacts to forward and reverse
traveling 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).
vs. 
The simple relationships:
can be used to convert between the standing wave ratio ( and the reflected/
forward power ratio , which can be directly read from the Thruline
Wattmeter. The relationship between and is graphed in Figure 3 and
Figure 4 .
Note: Attenuation, measured in dB, can be derived from the
power ratio by the equation Ndb = 10 log .
VSWR scales and their attendant controls for setting the reference point have
been intentionally omitted from the Bird 4304A. 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.
and
Where = VSWR
and = Wr/ Wf
W1WattsIntoLoad W fWr –==
1+ 
1–
----------------= 1–
1+
------------=
2

Theory of Operation
5
A trial is suggested – forget about VSWR for a few days and think in terms of =
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.
Figure 3 Percent Reflected Power vs. VSWR (1.0 – 1.3)

RF Directional Thruline® Wattmeter 4304A
6
Figure 4 Percent Reflected Power vs. VSWR (1.0 – 8.0)

Theory of Operation
7
Component Testing
The Bird 4304A is very helpful in component testing, and may be employed in
several ways:
Note: Measuring small attenuations requires correction for nor-
mal instrument errors. For two wattmeters, do this by simply con-
necting the wattmeters directly, with no line between them, and
adjusting their zero settings. For one, make sure to note exact
readings, or their difference, on the initial equality check, and cor-
rect for this.
Insertion VSWR or may be measured by placing the component
between the wattmeter and a good load resistor.
Attenuation (power lost by heat in a line) as well as insertion VSWR or
may be measured by inserting the unknown line between two
Thruline wattmeters, or between a Thruline wattmeter and a
Termaline absorption wattmeter.
Line loss using open circuit calibration: The high directivity of elements
can be exploited in line loss measurements by having the load
connector open or short circuited. The forward and reflected waves
then have equal power, so that = 100% and = . Open circuit
testing is preferred, because a high quality open is easier to create than
a high quality short. To measure insertion loss, use an open standard to
check forward and reverse power equality, then connect an open,
unknown line to the wattmeter. The measured is the attenuation for
two passes along the line (down and back). This can then be compared
with published data for line type and length (remember to halve Ndb or
double the line length).
Note: This measurement should be supplemented with either
time domain reflectometry or DC continuity and leakage checks,
since the attenuation measurement alone cannot detect faults
such as open or short circuits partway down the line.

RF Directional Thruline® Wattmeter 4304A
8
Impedance Mismatch
In some cases it may be necessary to use the Bird 4304A with a non-50
transmission line. If the reflected power is less than 10% and the frequency is
below 200 MHz, the resulting mismatch will not be too serious. At higher
frequencies or reflected power levels, the load impedance will change when the
wattmeter is removed.
When the line and load impedances are known, the system’s VSWR equals the
ratio of the two. Always divide the larger impedance by the smaller, since VSWR
must be greater than 1.
Example - Consider using a Bird 4304A to tune a 70line. If the
load impedance is also 70, the wattmeter will measure a VSWR
of 70/50 = 1.4. However, if you remove the wattmeter, the VSWR
will actually be 1.0. Similarly, if the load impedance is 35.7, the
VSWR will be 50/35.7 = 1.4 with the wattmeter and 70/35.7 = 2.0
without it. Caution must therefore be used, since both good and
bad matches can have the same measured VSWR. In this case, the
correct impedance can be determined by slightly changing the load
impedance. When the load impedance is near 70, the Bird 43 will
read increasing VSWR as the load impedance is increased.
Note: When working with non-50lines, it is especially import-
ant to calculate the exact load power by subtracting the reflected
power from the forward power.

9
Chapter 3 Installation
When transporting the Bird 4304A, turn the element so that the arrow points
down and set the range switch to 5 W. This will shunt the meter circuit and
protect the meter by dampening needle action.
Connections
Insert the Bird 4304A in coaxial transmission lines of 50nominal impedance.
The RF source can be connected to either side of the wattmeter without
affecting readings.
If non-50cables are used, a mismatch will occur causing inaccuracies in
readings. It is strongly advised that this condition be avoided. If this is not
possible, refer to "Impedance Mismatch" on page 8 for instructions on how to
calculate the actual VSWR.
Load Matching
When a Bird 4304A is used to tune a load to a transmitter and a good match is
obtained, removing the wattmeter will not change the match quality. A 50
load can terminate a 50transmission line of any length without altering
conditions at the transmitter. The wattmeter is just an additional length of 50
line.
When the load is not well matched, e.g. an antenna with a VSWR of 2.0, the line
length between load and transmitter will transform the impedance as seen at
the transmitter. Removing the wattmeter shortens the total line length by four
inches plus two connectors. This is still not significant at low frequencies where
four to five inches is a small fraction of a wavelength, but at higher frequencies
the transmitter’s frequency or power output may be affected.
WARNING
Never attempt to connect or disconnect RF equipment from the transmission
line while RF power is being applied.
Leaking RF energy is a potential health hazard.
CAUTION
Do not drop. Calibration could be disturbed or the meter could be damaged as
a result.

RF Directional Thruline® Wattmeter 4304A
10
Transmission line theory shows that if the line length changes by exactly 12
wavelength, the impedance at the transmitter will not change. So, to have
identical match with the Bird 4304A in or out of the circuit, it is necessary to
insert or remove 12wavelength of line (including the wattmeter). Use a length
of cable which, when added to the wattmeter, equals 12wavelength at the
frequency of interest. If more than one frequency is involved, a separate cable
length is required for each. See Figure 5 for sample cable lengths.
Note: Cable length is measured from end to end of the outer con-
ductor of the connectors, except for UHF and mini-UHF plugs where
it is measured from tip to tip of the center pins.
Note: Dimensions shown are for solid polyethylene cable such as
RG-58C/U or RG-8/U, which have a velocity of propagation 66% of
that of air. If RG-58 or RG-8 type cables with foam polyethylene
(v.p. of 79%) are used, multiply the dimensions in the graph by the
ratio of the relative velocities; 79% ÷ 66% = 1.2 in this case.