BIRD 4391A User manual

Multi-purpose
Thruline®Wattmeter
Rf Power Analyst®
Model 4391A
Cable And Antenna Tester
For Wireless Systems
Operation Manual
©Copyright 2016 by Bird Technologies, Inc.
Instruction Book Part Number 920-4391A Rev. K
Thruline® and Power Analyst® are Registered Trademark 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
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.

Multi-Purpose Thruline Wattmeter RF Power Analyst
iii
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.
On pages 15 and 17.
On pages 16.
On pages 21.
WARNING
Use only Nickel Metal Hydride (NiMH) batteries that have a minimum
capacity of 4500 milliampere hours (mAh). Do not install batteries that are
not Nickel Metal Hydride. Do not install NiMH batteries that have less than
4500 mAh capacity. Failure to comply may result in damage to the
batteries, damage to the instrument, and injury to personnel from battery
chemicals.
WARNING
Use dry cleaning solvents in a well ventilated area. Avoid excessive inhalation
of solvent fumes, since they can be toxic in heavy concentrations. Always
wear eye protection and avoid skin contact with the solvent.
WARNING
Ensure that the power cable is unplugged before opening the wattmeter
case. The power supply capacitor, C1, can retain a dangerous charge that
must be removed before touching. Always have another person standing by
who is trained in electric shock first aid.

Safety Precautions
iv
Caution Statements
The following equipment cautions appear in the text and are repeated here for
emphasis.
On pages 6 and 15.
On page 6.
On page 8.
On page 8.
On page 19.
CAUTION
Long-term storage of this instrument can affect battery performance and
reduce battery life. Do not store the instrument for long periods of time
without recharging the batteries (refer to page 17). Failure to comply may
result in reduced battery charge and shortened battery life.
CAUTION
Always be certain the 115/230 voltage selector is set to the proper voltage
before AC power is applied.
CAUTION
Never apply RF power to the Model 4391A Wattmeter unless both line
section sockets are filled with either an element or a dust plug. If an element
is used it is advisable to place the element with the arrow at a 90° angle to
the coaxial line.
CAUTION
Always disconnect AC power before opening the Model 4391 enclosure.
Removal of at least one battery cell is also recommended when servicing the
instrument.
CAUTION
If the element cannot be fully inserted into the socket, do not force it. You
might damage the element.

Multi-Purpose Thruline Wattmeter RF Power Analyst
v
On page 21.
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
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.
CAUTION
This instrument contains static sensitive electronic components. Before
opening or servicing the unit, make sure that you understand and practice
electrostatic discharge component handling. Failure to comply may result in
permanent damage to sensitive components.

Safety Precautions
vi
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.

Multi-Purpose Thruline Wattmeter RF Power Analyst
vii
UNITS ARE EQUIPPED WITH RECHAREABLE BATTERIES.
THESE ARE TO BE REPLACED BY AUTHORIZED SERVICE
PERSONNEL ONLY!!!
LAS UNIDADES VIENEN EQUIPADAS CON BATERIAS
RECARGABLES.
¡¡¡Y SOLAMENTE EL PERSONAL DE SERVICIO AUTORIZADO PUEDE
REEMPLAZARLAS!!!
GERÄTE SIND MIT WIEDER AUFLADBAREN BATTERIEN
BESTÜCKT.
BATTERIEN SIND NUR VON QUALIFIZIERTEM SERICE PERSONAL
AUSZUWECHSELN!!!
CES DISPOSITIFS SONT ÉQUIPÉS DE BATTERIES
RECHARGEABLES.
SEUL LE PERSONNEL D’ENTRETIEN AUTORISÉ EST HABILITÉ À
LES REMPLACER !
LE UNITÀ SONO DOTATE DI BATTERIE RICARICABILI,
CHE DEVONO DA COME SPECIFICATO DAL PRODUTTORE LA
PROTEZIONE DI SICUREZZA POTREBBE VENIRNE
COMPROMESSA.

Safety Precautions
viii
USE CORRECT VOLTAGE SETTING AND FUSE - SEE MANUAL.
UTILISER UNE TENSION ET UN FUSIBLE CORRECTS - CONSULTER
LE MODE D'EMPLOI.
USE LA INSTALACION Y FUSIBLE DE VOLTAJE CORRECTO - VEA
EL MANUAL.
AUSSCHLIESSLICH VORSCHRIFTSMÄSSIGE
WECHSELSPANNUNGS-EINSTELLUNG UND SICHERUNG
BENUTZEN - SIEHE DAZU HANDBUCH.
UTILLIZZARE TENSIONE E FUSIBLE ADATTI - FARE RIFERIMENTO
AL MANUALE.
BE SURE THE 115/230V AC VOLTAGE SELECTOR IS SET TO THE
PROPER LINE VOLTAGE, AND THE CORRECT AC LINE FUSE IS
INSTALLED BEFORE AC POWER IS APPLIED.
S'ASSURER QUE LE SÉLECTEUR DE TENSION 115/230V C.A. EST
BIEN RÉGLÉ POUR LA TENSION DU RÉSEAU ET QUE LE FUSIBLE
DE LIGNE C.A. CORRECT EST EN PLACE AVANT DE METTRE SOUS
TENSION C.A.
CERCIORESE QUE EL SELECTOR DE VOLTAJE DE 115/230V CA
ESTE COLOCADO A LA LINEA DE VOLTAJE APROPIADA Y QUE EL
FUSIBLE ESTE INSTALADO A LA LINEA CA ANTES DE APLICAR LA
CORRIENTE ALTERNA.
VOR EINSCHALTEN DER WECHSELSTROMZUFUHR
SICHERSTELLEN, DASS DER 115/230V WECHSELSPANNUNGS-
SELEKTOR AUF DIE VORSCHRIFTSMÄSSIGE
LEITUNGSSPANNUNG EINGESTELLT UND DIE RICHTIGE
WECHSELSTROM-HAUPTSICHERUNG EINGESETZT IST.
PRIMA DI EROGARE CORRENTE, ASSICURARSI CHE IL
SELETTORE DI VOLTAGGIO 115/230 V.C.A. SIA REGOLATO
CORRETTAMENTE E CHE IL FUSIBLE ADATTO ALLA LINEA DI
ALIMENTAZIONE C.A. SIA INSTALLATO.

Multi-Purpose Thruline Wattmeter RF Power Analyst
ix
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.

About This Manual
x
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.
Chapter Layout
Introduction — Introduces the external features and functions of the unit,
equipment provided, and options available.
Theory of Operation — Describes the overall operation of the circuitry and
the instrument functions.
Installation — Provides information about connecting the instrument to your
equipment.
Operation — All instructions necessary to operate the equipment, are
contained in this section.
Maintenance — If a failure should occur, the troubleshooting section will aid
in isolating and repairing the failure.
Parts — For location of major assemblies or parts refer to the part lists and
associated drawings.
4391A

xi
Table of Contents
Safety Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i
Safety Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Warning Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Caution Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
Safety Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v
About This Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x
Changes to this Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x
Chapter Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . x
Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Purpose and Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Chapter 2 Theory of Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Description of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Keyboard, Range Switches, and Display Group . . . . . . . . . . . . . . . . . . . . . 3
Elements, Analog Circuitry, and A/D Converter . . . . . . . . . . . . . . . . . . . . 4
Chapter 3 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Operating on AC Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Chapter 4 Operating Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Operating Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Reading Forward CW Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Reading Reflected CW Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Reading SWR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Measuring Peak Envelope Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Measuring Amplitude Modulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Measuring Power in dBm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Measuring Return Loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Insertion Loss or Attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Monitoring Maximum and Minimum Readings . . . . . . . . . . . . . . . . . . . 13
Using the Peaking Aid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Battery Care . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Table of Contents
xii
Chapter 5 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Preventive Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Cleaning and Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Long-term Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Required Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Initial Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Element Wiper Contact Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Disassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Front Panel Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Main Printed Circuit (PC) Board Removal . . . . . . . . . . . . . . . . . . . . . . . . 22
QC Connectors Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Line Section Removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Battery Replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Customer Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Limited Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

1
Chapter 1 Introduction
The Model 4391A is a multi-purpose Radio Frequency wattmeter designed around
a microcomputer. A program stored in permanent memory controls the operation
of the instrument at all times, permitting the detection and correction of various
error sources and the refinement of the raw data produced by the directional
detectors. The instrument can compute VSWR, amplitude modulation, and
various decibel variables reducing the odds of error and making such
measurements consistent or repeatable regardless of who makes the
measurement.
Other benefits include extended range using standard elements in some modes
of operation, continuous monitoring of maximum and minimum readings, a
peaking aid, and error messages.
Because of its complexity, the proper use of the 4391A is not always obvious.
For this reason it is strongly advised that this manual be read in its entirety
before using the device.
Purpose and Function
The 4391A RF Power Analyst is an insertion type digital RF Directional Thruline®
Wattmeter designed to measure peak or average power flow, load match, and
amplitude modulation in 50 ohm coaxial transmission lines. It is intended for
use with CW, AM, FM, SSB, TV, and Pulse modulation envelopes. The instrument
directly reads PEP or CW power in watts, milliwatts, or kilowatts in 9 ranges
from 2.5 to 1000 full scale forward power and 0.25 to 100 full scale reflected
power depending on the Plug-in Element. In addition it reads SWR directly over
the range of 1.00 to 99.99, percent modulation directly over the range of 0.0 to
99.9, and return loss over the range of 0 to 36.1 dB. For convenience, forward
and reflected CW power can be displayed in dBm (dB above 1 milliwatt) from 6
dB above to 24 dB below nominal element range.
Power range and frequency band are determined by the Plug-in Elements used.
Two switches on the front panel of the instrument are set by the user to
correspond to the nominal power range of the forward element. The reflected
element is assumed to have a nominal range one tenth that of the forward
element.
In any mode of operation, the instrument can recall from memory the lowest or
highest reading taken or tell the operator whether the newest reading is less
than, equal to, or greater than the previous reading.

Introduction
2
Description
The instrument is housed in an aluminum case approximately 4-3/8 inches high
by 9-5/8 inches deep by 6-1/4 inches wide (111 mm x 244 mm x 159 mm)
including connections, see Figure 1 . At each end of the line section are Bird
Quick-Change type RF connectors which may be easily interchanged with any
other Bird QC connector. See Bird Catalog for types available.
Operating power is derived from rechargeable nickel metal hydride batteries
inside the unit or from a 115/230 VAC power source connected to the unit
through the power cord supplied with the unit.
Figure 1 Outline Drawing

3
Chapter 2 Theory of Operation
Description of Operation
Figure 2 is a block diagram of the major functional parts of the Model 4391A RF
Wattmeter. The Microcomputer integrated circuit shown, controls all the other
portions of the instrument, which fall into two major groups.
Figure 2 Circuit Block Diagram
Keyboard, Range Switches, and Display Group
The keyboard and range switches serve only to pass information to the computer.
The display, of course, returns information from the computer to the operator.
The display, which is comprised of four seven-segment LED digits, is strobed digit
by digit left to right at a rate of approximately one digit per millisecond. This
serves to conserve battery power and drive circuitry while providing scanning for
the columns of the keyboard. Each time a digit is strobed, the corresponding
column of the keyboard is read and if a key is pressed, the computer puts the code
for that key into a memory cell. The nine mode keys select which parameter is to
be measured. The three modifier keys simply modify the way in which the result is
displayed. The range selector switches identify to the computer the nominal full
scale values of the elements used. They have no effect on input sensitivity, which
is determined by the elements.

Theory of Operation
4
Elements, Analog Circuitry, and A/D Converter
These components are controlled by the computer. The Plug-in Elements in the
line section provide low level positive voltages related to the instantaneous
value of power (see Figure 3 ). The first group of solid state switches selects the
forward element, the reflected element, or ground as the input to the
preamplifier which boosts these signals to 0.1 to 2.0 volt range. The remaining
switches shown as two groups direct the output of the preamp to the analog-to-
digital converter either directly or through a peak or negative peak detector.
The analog-to-digital converter converts the voltage to a 15 digit binary
number.
Each reading output by the display is derived from up to three voltage readings
using the circuitry described above. Once these voltages are measured, all
remaining operations are performed within the computer chip as follows:
The voltages are corrected for error due to DC drift in the analog circuitry. Each
voltage is converted to square root of power using stored data tables. These
values are then combined mathematically to arrive at the final result in binary.
This is used to update the registers containing the last value, the maximum value,
or the minimum value as required. Finally, the result is converted to a decimal
number and placed into a register from which the display driving routine
operates.
Figure 3 Plug-In Element Schematic Diagram
The coupling circuit that samples the traveling waves is in the Plug-in Element.
The circuitry of the element and its relationship to the other components of the
Thruline Watt-meter are illustrated in the schematic diagram. Energy will be
produced in the coupling circuit of the element by both mutual inductance and
capacitance from the traveling RF waves of the line section. The inductive
currents will flow according to the direction of the traveling waves producing
them. The capacitive portion of these currents is independent of the direction
of the traveling waves. Therefore, assuming that the Plug-in Element remains

Multi-Purpose Thruline Wattmeter RF Power Analyst
5
stationary, the coupling currents produced from the waves of one direction will
add in phase, and those produced from waves of the opposite direction will
accordingly subtract in phase. The additive or “arrow” direction is assigned to
the forward wave.
The electrical values of the element circuits are carefully balanced and designed
so that current from the reverse wave will cancel the other almost completely.
The result is directivity always higher than 25 dB, which means that the element
is highly insensitive (nulled) to the REVERSE direction wave. Being highly
directional, the Thruline element is sensitive (at one setting) only to one of the
traveling waves that produce standing waves by interference. Thruline
Wattmeter measurements are, therefore, independent of position along
standing waves.
Figure 4 Readings with Various Envelopes

6
Chapter 3 Installation
The Model 4391A RF Power Analyst is completely portable and very suitable for
field or laboratory use. Its power is derived from rechargeable nickel metal
hydride batteries inside the unit or from an AC outlet via the power cord
supplied with the device.
The batteries are shipped in a low charge state. It is, therefore, recommended that
you charge the instrument for 16 hours before using it for continuous operation.
Note: Battery charging at temperatures greater than 46° C (115°
F) can result in reduced operational time.
Operating on AC Power
For AC power operation, the Model 4391A is simply connected to an AC
receptacle using the line cord provided. The correct AC voltage is selected via a
rear panel switch ( Figure 5 ). The meter may be operated in this manner with
the batteries removed if desired.
Figure 5 Rear Panel
CAUTION
Long-term storage of this instrument can affect battery
performance and reduce battery life. Do not store the
instrument for long periods of time without recharging the
batteries (refer to page 17). Failure to comply may result in
reduced battery charge and shortened battery life.
CAUTION
Always be certain the 115/230 voltage selector is set to the
proper voltage before AC power is applied.
Item No. Description
1AC input voltage selector switch
2Fuse holder
3AC power cable connector

Multi-Purpose Thruline Wattmeter RF Power Analyst
7
Connections
The Model 4391A contains a short section of rigid 50 ohm coaxial air dielectric
transmission line. To make measurements relating to the traveling waves in a
coaxial line, that line must be disconnected at some convenient point to permit
the Model 4391A air line to be inserted.
Although the Model 4391A is normally supplied with two Female N-type
connectors, a variety of easily interchangeable connectors are available to
facilitate connecting to the user’s system.
Once the Model 4391A is installed in the coaxial line, a Plug-in Element or a pair
of Plug-in Elements must be selected which correspond to the frequency and
power levels to be measured.
Note: The instrument is shipped with dust plugs installed in the
element sockets. Remove the dust plugs to insert elements.
In order to take full advantage of the Model 4391A’s capabilities, two elements in a
10:1 ratio of power range should be used. If only one element is used, the other socket
should be filled with a dust plug or a higher power element. Also, for greatest
accuracy, the element(s) should be chosen having the lowest possible power range
that will not result in over-ranging. Table 1 lists elements required for each mode of
operation.
Table 1 - Plug-In Elements Required
The higher power element is placed in the socket marked “FORWARD” and its
arrow pointed in the direction of forward power flow (toward antenna or load).
The lower power element is placed in the socket marked “REFLECTED” and is
normally pointed in the direction opposite to forward power flow. The elements
are clamped in place by the hold-down catches on the face of the line section.
These catches must be used to avoid error due to the element not contacting
the bottom or seating plate of the socket. With the element(s) in place, set the
range switches to correspond with the nominal power range of the elements.
For example, if the forward element is a 5 watt element, the switches are set at
5 and x1. For a 250 watt element they are set at 2.5 and x100. Sometimes it is
necessary to use milliwatts or kilowatts as the unit of measure. In other words,
1 watt becomes 10 x 100 milliwatts and 2500 watts becomes 2.5 x 1 kilowatts.
Mode Forward Reflected
FWD CW 3
RFL CW 3
SWR 33 †
† The reflected element must have a nominal power
range one tenth that of the forward element.
FWD PEP 3
RFL PEP 3
% MOD 3
FWD dBm 3
RFL dBm 3
RTN Loss 33 †