RF DIRECTIONAL
THRULINE® WATTMETER
MODEL APM–16
©Copyright 2013 by Bird Electronic Corporation
Instruction Book Part Number 920-APM16 Rev. E
Thruline® and Termaline® are registered trademarks
of Bird Electronic Corporation
I am not blank
16
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 uniterruptible 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.
i
Safety Symbols
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.
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 warnings appear in the text where there is danger to operating
and maintenance personnel, and are repeated here for emphasis.
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.
Refer to page 11.
WARNING
RF voltage may be present in element socket. Keep element in socket during
operation.
Refer to pages 11 and 13.
ii
Caution Statements
The following equipment cautions appear in the text and are repeated here for
emphasis.
CAUTION
For low reflection measurements, do not rotate the reflected power element
to read forward power. Damage to the element or wattmeter could result.
Refer to page 8.
CAUTION
To prevent damage from battery leakage, remove the battery if the unit will
not be used for more than two weeks.
Refer to pages 11 and 24.
CAUTION
Do not attempt to remove the RF center conductor. This will damage the line
section.
Refer to page 20.
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
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.
iv
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.
v
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.
vi
About This Manual
This manual covers the operating and maintenance instructions for the following models:
APM-16
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 Bird SignalHawk, lists equipment
supplied and optional equipment, and provides power-up instructions.
Installation — Describes how to connect SignalHawk to the user’s system,
describes the vector network analyzer measurements, and provides quick start
steps for each measurement.
Operation — Describes the power measurement feature, lists compatible
power sensors, describes how to connect SignalHawk to the user’s system, and
provides quick start steps to make power measurements.
Maintenance — Lists routine maintenance tasks as well as troubleshooting
for common problems. Specifications and parts information are also included.
vii
Bird Technologies
Table of Contents
Safety Precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i
Safety Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Warning Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Caution Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
Safety Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iv
About This Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .vii
Changes to this Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Literature Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Chapter Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Chapter 2 Theory of Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Traveling Wave Viewpoint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Coupling Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Load Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Standing vs. Travelling Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
vs.
Low Reflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Transmitter Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Component Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Frequency Response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Impedance Mismatch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Chapter 3 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Connecting RF Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Absorption Wattmeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Chapter 4 Operating Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Normal Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Load Matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Chapter 5 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Maintenance Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Contact Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Zero Adjust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
viii
Repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
“QC” Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Relpacing the Meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Replacing the Instrumentation Module . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Calibration Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Equipment Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Calibrating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Customer Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Replacement Parts List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Available “QC” Type Connectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Limited Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
ix
Bird Technologies
x
Chapter 1 Introduction
The Bird APM-16 is an insertion wattmeter designed to measure RF power and
load match in 50 ohm transmission lines. It has a maximum VSWR of 1.05 for
frequencies up to 1000 MHz. The meter provides direct readings in watts with
an expanded linear 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).
Description
The Bird APM-16 is portable and rugged, with an aluminum housing. For additional protection, the microammeter is specially shock mounted. Bumpers on
the base and back allow the meter to stand or lie flat. Refer to Figure 1 to
identify components.
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.
Figure 1 Outline Drawing
1
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 Ef and current If in 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 Ir in phase, with Er / Ir = Zo.
Each wave is mathematically simple and has a constant power:
Wf = Watts Forward = E
Wr = Watts Reflected = E
2
/ Zo = I
f
2
r
Zo is 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 APM-16 is a
length of uniform air line with Zo = 50 ohms.
Coupling Circuit
/ Zo = I
2
Zo = Ef I
f
2
Zo = Er I
r
f
r
The Bird Plug-In Element contains a coupling circuit that samples the travelling
waves. The element circuitry and its relationship to the rest of the Bird APM-16
are illustrated in Figure 5.
Figure 2 Schematic
3
Current is produced in the coupling circuit by the travelling waves in the line
section. Both inductive and capacitive coupling contribute to this. Inductive current flows in the direction of the travelling wave, while the capacitive current is
independent of the direction of the travelling wave. Therefore, the inductive
current produced by one travelling wave will add in phase with the corresponding 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 APM-16 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 equal
(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, given by:
Wl = Watts into Load = Wf – W
Good load resistors, such as Bird Termaline Loads, will give negligible reflected
power.
r
Standing vs. Travelling Waves
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 except for the
phase angle of the reflection coefficient (distance, load to minimum).
4
vs.
2
The simple relationships:
Where
1+
--------------- -=
and
1 –
can be used to convert between the standing wave ratio ( and the reflected/
forward power ratio , which can be directly read from the Thruline Wattme-
ter. 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 APM-16. Experience using the Thruline
Wattmeter for transmitter tune-up, antenna matching, etc. will show that the
power ratio measurement is as useful as the standing wave ratio.
A trial is suggested – forget about VSWR for a few days and think in terms of =
Wr / Wf. The meter readings, Wr and 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 in the reflected power position.
1–
=
------------
1+
= VSWR
and = Wr / W
f
5
Figure 3 Percent Reflected Power vs. VSWR (1.0 – 8.0)
6
Figure 4 Percent Reflected Power vs. VSWR (1.0 – 1.3
7
Low Reflection
= 10% ( = 2) is the typical limit of antenna match. Further effort is frequently
not worthwhile because below this level reflected power is hard to measure,
and Wl can not be significantly increased. TV and VHF transmitters are examples
of systems requiring lower reflected power but for reasons other than maximizing power transmission.
CAUTION
For low reflection measurements, do not rotate the reflected power element
to read forward power. Damage to the element or wattmeter could result.
When the same element is used to measure both forward and reflected power,
meaningful readings are possible down to about = 5% ( = 1.5). For accurate
measurement of very low levels of reflected power, i.e. = 0.6% ( = 1.17), use
a second element rated at one tenth of the full scale power of the forward element. This method should not be used with element ranges differing by more
than 10:1.
For example, consider an 80 watt transmitter and a Bird APM-16 with 100 and
10 watt elements. Measure Wf with the 100 W element. Measure Wr with the
10 W element (make sure the arrow points towards the transmitter). Wr can be
measured down to at least 0.5 W, so that = 0.5 / 80 or about 0.6%, corresponding to = 1.17.
Transmitter Monitoring
The Thruline Wattmeter can be used for continuous monitoring of transmitter
output or reflected power, for instance while checking intermittent antenna or
line faults.
Component Testing
The Bird APM-16 is very helpful in component testing, and may be employed in
several ways:
1. Insertion VSWR or can be measured by placing the component between
the wattmeter and a good load resistor.
2. Attenuation (power lost by heat in a line) as well as insertion VSWR or can be
measured by inserting the unknown line between two Thruline Wattmeters, or
between a Thruline Wattmeter and a Termaline Absorption Wattmeter.
Note: Very small attenuations require allowance for normal instrument errors. To correct for this without any calculations, connect the
wattmeters directly, with no line between them, and adjust their zero
settings.
8
3. Line loss using open circuit calibration: The high directivity of elements can
be exploited in line loss measurements, because of the equality of forward
and reflected power with the load connector open or short circuited. In this
state the forward and reflected waves have equal power, so that f = 100%
and r = ¥. Open circuit testing is preferred to short circuit, because a high
quality open circuit is easier to create than a high quality short.
To measure insertion loss, use a high quality open circuit to check forward
and reverse power equality, then connect an open-circuited, unknown line
to the wattmeter. The measured f is the attenuation for two passes along
the line (down and back). The attenuation can then be compared with published data for line type and length (remember to halve Ndb or double the
line length to account for the measurement technique).
This measurement should be supplemented by either time domain reflectometry or DC continuity and leakage checks, since the attenuation measurement alone cannot account for faults such as open or short circuits
partway down the line.
Note: Very small attenuations require allowance for normal instrument errors. Make sure to note exact readings, or their difference,
on the initial equality check, and correct for this.
Frequency Response
Bird Plug-In Elements have a flat frequency response over their specified operating range. A sample set of curves is shown in Figure 5. Notice that for the low
power element, the rolloff outside its frequency band is more pronounced than
for the high power elements. For example, at 40 MHz the 10C element will have
a loss of 4 dB, giving a reading of about 40% of the true value For the 100C, the
loss will only be about 1 dB, for a reading at 80% of the true value, and the 500C
should be within the normal 5% of full scale tolerance.
Figure 5 Representative Frequency Response
9
These curves are typical for all element types (H, A, B, C, D, ...) at their respective frequencies. Since C elements have a frequency range of 100 - 250 MHz,
response curves for other element types can be approximated by replacing the
100 and 250 MHz points on the chart with the extremes of the element’s frequency range, and recalculating the other frequency points accordingly. For
example, for a B element (range 50 - 125 MHz) simply divide all frequencies by
two. For an E element (range 400 - 1000 MHz) multiply all frequencies by four.
Harmonics or subharmonics that lie outside of the frequency range of the element may exist in the circuit under test. A rough approximation of the element’s response to harmonics can be made with these curves. Using an element
for measurements outside of its frequency range is not recommended. The
response curves presented are only typical, and not guaranteed.
Impedance Mismatch
There may be cases where it is necessary to use the Bird APM-16 with a non-50
ohm 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 higher reflected power levels, the load impedance will change when
the wattmeter is removed from the circuit.
When the line and load impedances are known, the system’s VSWR can be calculated by dividing the larger impedance by the smaller. Remember that the
VSWR ratio must always be greater than 1.
For example, consider using a Bird APM-16 to tune a 70 ohm line. If the load
impedance is also 70 ohms, the wattmeter will measure a VSWR of 70 / 50 = 1.4.
However, if you remove the wattmeter, the VSWR will actually be 1.0. If the
load impedance is 35.7 ohms instead, 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 ohms, the Bird 43 will read increasing VSWR as the load impedance is increased.
Note: When working with non-50 ohm lines, it is especially import-
ant to calculate the load power by subtracting the reflected power
from the forward power.
10
Chapter 3 Installation
CAUTION
To prevent damage from battery leakage, remove the battery if the unit will
not be used for more than two weeks.
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.
Battery
The 9 V battery must be installed before operation. Figure 1 on page 1 shows
the location of the battery access door. Slide this open and connect the battery.
When transporting or storing the Bird APM-16, be sure the power switch is set
to OFF. In any other position, there is a slight drain on the battery.
WARNING
RF voltage may be present in element socket. Keep element in socket during
operation.
Elements
The Bird APM-16 uses Bird Plug-In Elements to make measurements. The element’s frequency range and maximum power are listed on its label. The transmitter test frequency should be within the band of the element used. The arrow
on the element points in the direction of power flow that the meter will read.
To make measurements, insert an element into the line section socket and
rotate it against one of the stops. Contacts on opposite sides of the element
connect with a spring finger in the socket when the element is in the forward or
reverse position. A small catch at the corner of the socket face presses on the
shoulder of the element to keep it in proper alignment (see Figure 6).
11
Figure 6 Securing an element
Connecting RF Power
Insert the Bird APM-16 in 50 ohm coaxial transmission lines. The RF source can
be connected to either side of the wattmeter.
Absorption Wattmeter
Combining the Thruline Wattmeter with a Bird Termaline Load 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.
12
Chapter 4 Operating Instructions
WARNING
RF voltage may be present in element socket. Keep element in socket during
operation.
Normal Operation
1. Insert the element in the line section socket.
2. To measure forward power, turn the element so that the arrow points
towards the load.
3. To measure reflected power, turn the element so that the arrow points
towards the source.
4. Turn on the RF source.
5. Read the power using the scale whose full-scale marking matches the element’s maximum power.
Figure 7 Element Direction
For your convenience, a pair of VSWR conversion graphs are included in this
manual. With these charts, VSWR can be determined from the forward and
reflected power. Find the intersection of the forward and reflected power measurements. The slanted line passing closest to this point is the VSWR.
13
Figure 8 VSWR Conversion Graph (Reflected Power 0.2 – 20.0)
\
14
Figure 9 VSWR Conversion Graph (Reflected Power 0.01 – 1.00)
15
Load Matching
When a Bird APM-16 is used to tune a load to a transmitter and a good match is
obtained, removing it will not change the match quality. A good 50 ohm load
can terminate a 50 ohm transmission line of any length without altering conditions at the transmitter. The wattmeter is just an additional length of 50 ohm
line in series with the measurement.
When the load is not well matched, e.g. an antenna with a VSWR of 1.5 or 2.0,
the line length between the load and the transmitter will transform the load
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 frequency or power output of the transmitter may be
affected.
Transmission line theory shows that if the line length changes by exactly 12
wavelength, the impedance at the transmitter is unchanged. To have identical
match quality with the Bird APM-16 in or out of the circuit, it is necessary to
insert or remove 12 wavelength worth of line (including the wattmeter). To do
this, use a length of cable which, when added to the wattmeter, equals a 12
wavelength at the frequency of interest. If more than one frequency is involved,
a separate cable length is required for each. See Figure 10 for sample cable
lengths.
Note: Cable length shown (in inches) is measured from end to end of
the outer conductor of the connectors, except for UHF or mini-UHF
plugs where the cable length is measured from tip to tip of the center
pins.
Note: Dimensions shown are for solid polyethylene cable like
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 containing foam polyethylene
(velocity of propagation of 79%) are used, the dimensions in the graph
must be multiplied by the ratio of the relative velocities; 79% ÷ 66% =
1.2 in this case.
16
Figure 10 Cable Length / Wavelength Matching
17
18
Chapter 5 Maintenance
The rugged and simple design of the Bird APM-16 means that it requires minimal routine maintenance.
Troubleshooting
The following table contains troubleshooting information for problems that can
occur during normal operation. Find the problem on the table, review possible
causes, and perform the corrective action listed.
This manual does not list all malfunctions that may occur, or all corrective
actions. If a malfunction is not listed or not corrected by the listed actions, contact the nearest Bird Service Center for assistance.
Problem Possible Cause Corrective Action
No meter reading No RF power Check RF source
Intermittent or
inconsistent meter
readings
High VSWR or
reflected power
“Arrow” on element
pointing wrong way
Battery drained Check the battery and
DC contact bent Adjust contact (page 20)
Open or short circuit in
meter leads
Meter burned out or
damaged
Dirty DC contact on element
Faulty transmission line
or antenna
Sticky or defective
meter
Foreign material in line
section or in RF connectors
Open or shorted transmission line
Bad load or poor connectors
Rotate element
replace if necessary
Replace defective leads
Return wattmeter for service
Clean contact (page 20)
Inspect line
Return wattmeter for service
Clean connectors (page 20)
Inspect line
Inspect load, antenna, and
connectors
19
Maintenance Procedures
Cleaning
It is important to keep the following surfaces clean:
Socket bore
DC contacts on the element
Teflon insulators
If any of the contacts or line connectors are dirty, clean them with a cotton
swab dipped in commercial contact cleaner or isopropyl alcohol.
CAUTION
Do not attempt to remove the RF center conductor. This will damage the line
section.
If the RF line section seems dirty, do not loosen any connections. Clean accessible components as described above and use dry, clean air to blow out the interior.
The outside of the meter housing can be cleaned with a soft cloth dampened
with a mild detergent solution. Do not wipe the meter glass with a dry cloth, or
a static charge could develop that would cause an erroneous meter indication.
Contact Adjustment
When cleaning the socket bore, do not disturb the spring finger of the DC contact. If necessary, the contact can be adjusted manually. The button must be out
far enough to maintain good contact, but not so far as to interfere with easy
entry of the element body.
Battery
The accuracy of the unit may be reduced by a weak battery. To check the condition of the battery, set the power switch to BAT. If the pointer does not swing
into the BATTERY TEST region, replace the battery.
Zero Adjust
The meter’s zero setting should be checked when no RF power is present. When
no power is applied the pointer should rest exactly on zero. If adjustment is
required, set the power switch to OFF and turn the zero screw until the pointer
is set at zero (See Figure 1 on page 1 for screw location).
20
Repair
“QC” Connectors
The Bird 43 is normally supplied with Quick-Change Female N type connectors.
Other Bird “QC” connectors are available (See “Available “QC” Type Connectors” on page 28). To change a QC connector, remove the
8-32 screw at each corner of the connector and then pull it straight outward.
Reverse this to install the new connector.
Relpacing the Meter
1. Remove the back cover.
2. On the back of the meter, loosen both nuts securing the meter leads and
remove the leads.
3. Remove the large Phillips screws securing the meter shock ring.
Note: These screws are on either side of the housing, even with the
meter.
4. Pull the meter straight out.
Note: If necessary, the meter retaining ring and shock mount can be
removed.
5. Replace the meter by reversing the steps above.
Replacing the Instrumentation Module
Note: The instrumentation module contains the line section and cir-
cuit board chassis.
1. Remove the back cover.
2. Use a 0.050" hex wrench, turning clockwise, to loosen the set screw in the
power switch knob.
3. Pull the knob straight off.
4. Unsolder the leads on the top of the circuit board chassis.
Note: Note the color coding when unsoldering so the leads can be
returned to their original positions.
5. Remove the phillips screws on the front of the unit, on either side of the
element socket.
6. Pull the instrumentation module straight out.
7. Install a replacement module by reversing the steps above.
21
Calibration
Calibration of the Bird APM-16 will be required after replacing the meter or the
instrumentation module, and also when the calibration certification expires.
Note: Calibrating the unit, or disturbing the calibration label, within
the one-year warranty period will void the warranty.
Calibration Environment
For best results, make sure that the workspace meets the following requirements:
The workspace should be free from electrical noise and radiated sig-
nals. A Bird 43 equipped with a 4030 relative field strength element
can be used to check the area for spurious radiation. Make sure the
gain on the 4030 is set to maximum. If there is any meter deflection on
the 43, the area is unsuitable for calibration.
The workspace and equipment should be at a uniform and stabilized
temperature, between 20 and 25°C (68 to 77°F).
The relative humidity should be less than 50% and noncondensing.
Equipment Required
To calibrate the Bird APM-16, you will need the following equipment:
Standard digital multimeter with DC voltmeter resolution of 0.01 V or
better (Fluke Model 87)
Bird 4401A200 plug-in calibration element
Regulated DC power supply, supplying 2 ± 0.1 V
50 ohm coaxial cables (RG-58-U), no more than 3 feet (1 m) long
BNC “T” adapter
Figure 11 Calibration Setup
22
Calibrating
1. Remove any dust plug or element from the APM.
2. Allow the APM and all equipment to stabilize with respect to the workspace
environment.
Note: The APM and the calibration element may require up to 24
hours for complete stabilization if brought from an extreme storage
environment.
3. Set the APM to OFF.
4. Turn the zero screw until the pointer rests at zero (See Figure 1 on page 1
for screw location).
5. Switching between BAT and OFF, rezero until a repeatable zero is obtained.
6. Pierce the label inside the circle with an “X” in it (See Figure 1 on page 1 to
locate the hole).
Note: The calibration access hole is covered by a label showing the
calibration date.
Note: Disturbing the calibration label within the one-year warranty
period will void the warranty.
7. Connect the power supply, voltmeter, and calibration element as shown in
Figure 11 above.
Note: The APM does not need to be connected at this time.
8. Turn on the voltmeter and power supply.
9. Set the output to 2.00 ± 0.1 V. Allow the equipment to stabilize for the time
recommended by the manufacturer, but for no less than five minutes.
10. Set the APM to ON and allow it a minimum of five minutes to stabilize.
11. After the equipment has stabilized, check the battery in the wattmeter by
momentarily setting the power switch to BAT.
12. If the pointer does not swing into the BATTERY TEST region, replace the battery, set the switch back to ON, and allow the APM to stabilize for another
five minutes before continuing.
13. Insert the calibration element into the wattmeter.
14. Rotate it in either direction until it stops, then rotate it back 90° to short circuit the contact to the line section body.
15. Rotate the calibration element in either direction until it stops.
16. Adjust the calibration potentiometer (through the calibration access hole)
until the pointer rests at “25” on the upper scale.
23
Storage
CAUTION
To prevent damage from battery leakage, remove the battery if the unit will
not be used for more than two weeks.
When storing the meter, keep an element or dust plug in the element socket to
prevent the intrusion of dust and to prevent damage to the meter movement.
Be sure the power switch is OFF. In any other position, there is a slight drain on
the battery.
24
Customer Service
Any maintenance or service procedure beyond the scope of those in this chapter should be referred to a qualified service center.
If the unit needs to be returned for any reason, request an RMA through the
Bird Technologies website. All instruments returned must be shipped prepaid
and to the attention of the RMA number.
Bird Service Center
30303 Aurora Road
Cleveland (Solon), Ohio 44139-2794
Fax: (440) 248-5426
E-mail: bsc@bird-technologies.com
For the location of the Sales Office nearest you, visit our Web site at:
http://www.birdrf.com
25
Specifications
Frequency Range (Element
Dependent)
Power Range (Element
Dependent)
Impedance, Nominal 50 ohms
VSWR, Insertion 1.05:1 max 2 MHz – 1 GHz
Accuracy
10° to 35°C
–20° to +50°C
Peak/Average Ratio > 10 dB
Settling Time < 1 s
Meter Shock mounted linear scale with
Connectors Bird “QC” N Female normally supplied
Battery Standard 9V battery. 200 hours
Operating Position Any
EMC Complies with 89/336/EEC and 92/31/
Emissions Immunity Safety EN 55011:1991 Class B
2 MHz – 2.3 GHz
1 W – 1 kW
± 4% of reading ± 1% of full scale
± 6% of reading ± 2% of full scale
expanded scales of 25, 50 and 100 full
scale. Includes 5% overrange.
operation, minimum.
EEC
EN 50082-2:1995
EN 61010-1:1993 in accordance with
79/23/EEC and 93/68/EEC
Complies with IEC-1010-1,
UL-1244, and CSA-231
Temperature, Operating –4 to +122 °F (–20 to +50 °C)
Temperature, Storage –13 to +149 °F (–25 to +65 °C)
Humidity 90% noncondensing max
Dimensions (Nominal) 3-5/8”L x 4”W x 6-7/8”H
(92 x 102 x 175 mm)
Weight (Approx.) 4 lb. (1.8 kg) with N-Connectors
Finish Black Powder Coat
26
Replacement Parts List
Description Qty. Part Number
Housing Assembly 1 4401A002
Cover Assembly 1 4401A011
Line Section &
Instrumentation Module
Carrying Strap (Included in
Housing Assembly)
Dust Plug, Aluminum 1 3610-031
Selector Switch Knob 1 4401A014
Meter, DC 1 2080A070
Battery 1 5-1375
RF Connectors 2 See list below
1 4401A003
1 8580A003
27
Available “QC” Type Connectors
Connector Part Number
BNC-Female 4240-125
BNC-Male 4240-132
C-Female 4240-100
C-Male 4240-110
HN-Female 4240-268
HN-Male 4240-278
LC-Female 4240-031
LC-Male 4240-025
LT-Female 4240-018
LT-Male 4240-012
Mini UHF-Female 4240-346
N-Female 4240-062
N-Male 4240-063
Open Term.
# 10-32 Nut
SC-Female 4240-090
SMA-Female 4240-336
SMA-Male 4240-334
TNC-Female 4240-156
TNC-Male 4240-160
UHF-Female 4240-050
UHF-Male 4240-179
7/16” IEC (Jack)
Type 169-4
7/16” IEC (Plug)
Type 169-4
7/8” EIA 4240-002
1-5/8” EIA Fixed 4240-096
1-5/8” EIA Swivel 4240-208
4240-363
4240-344
4240-080
28
Limited Warranty
All products manufactured by Seller are warranted to be free from defects in
material and workmanship for a period of one (1) year, unless otherwise
specified, from date of shipment and to conform to applicable specifications,
drawings, blueprints and/or samples. Seller’s sole obligation under these
warranties shall be to issue credit, repair or replace any item or part thereof
which is proved to be other than as warranted; no allowance shall be made for
any labor charges of Buyer for replacement of parts, adjustment or repairs, or
any other work, unless such charges are authorized in advance by Seller.
If Seller’s products are claimed to be defective in material or workmanship or
not to conform to specifications, drawings, blueprints and/or samples, Seller
shall, upon prompt notice thereof, either examine the products where they are
located or issue shipping instructions for return to Seller (transportationcharges prepaid by Buyer). In the event any of our products are proved to be
other than as warranted, transportation costs (cheapest way) to and from
Seller’s plant, will be borne by Seller and reimbursement or credit will be made
for amounts so expended by Buyer. Every such claim for breach of these
warranties shall be deemed to be waived by Buyer unless made in writing
within ten (10) days from the date of discovery of the defect.
The above warranties shall not extend to any products or parts thereof which
have been subjected to any misuse or neglect, damaged by accident, rendered
defective by reason of improper installation or by the performance of repairs
or alterations outside of our plant, and shall not apply to any goods or parts
thereof furnished by Buyer or acquired from others at Buyer’s request and/or
to Buyer’s specifications. In addition, Seller’s warranties do not extend to the
failure of tubes, transistors, fuses and batteries, or to other equipment and
parts manufactured by others except to the extent of the original
manufacturer’s warranty to Seller.
The obligations under the foregoing warranties are limited to the precise terms
thereof. These warranties provide exclusive remedies, expressly in lieu of all
other remedies including claims for special or consequential damages. SELLER
NEITHER MAKES NOR ASSUMES ANY OTHER WARRANTY WHATSOEVER,
WHETHER EXPRESS, STATUTORY, OR IMPLIED, INCLUDING WARRANTIES OF
MERCHANTABILITY AND FITNESS, AND NO PERSON IS AUTHORIZED TO
ASSUME FOR SELLER ANY OBLIGATION OR LIABILITY NOT STRICTLY IN
ACCORDANCE WITH THE FOREGOING.
29
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