BIRD TERMALINE 8745 Series User manual

INSTRUCTION BOOK
TERMALINE®LOAD RESISTOR
SERIES 8745/8746
Bird® Electronic Corporation
30303 Aurora Road
Cleveland (Solon), Ohio 44139
Sales & Technical Support: 440-248-1200
866-695-4569 toll free
Sales email: [email protected]
Technical Support email: [e-mail]
©Copyright 2010 by Bird Electronic Corporation
Instruction Book Part Number 920-8745/46 Rev. C
Termaline®is a Registered Trademark
of Bird Electronic Corporation

I am not blank

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 publica-
tion. These precautions must be thoroughly understood and apply to all phases of
operation and maintenance.
Safety Symbols
 Note: Calls attention to supplemental information.
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.
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.

ii
Warning Statements
The following safety warnings appear in the text where there is danger to operat-
ing and maintenance personnel, and are repeated here for emphasis.
On page 7 and 9.
On page 10.
On page 14.
Caution Statements
The following equipment cautions appear in the text and are repeated here for
emphasis.
On page 7.
This symbol indicates that a shock hazard exists if the precau-
tions in the instruction manual are not followed.
The caution symbol appears on the equipment indicating there
is important information in the instruction manual regarding
that particular area.
This symbol indicates that the unit radiates heat and should not
be touched while hot.
This symbol appears on the equipment and indicates the
requirement for separate collection of discarded electrical and
electronic equipment in accordance with the European Union
Directive 2002/96/EC.
WARNING
Never attempt to disconnect the equipment from the transmission line while RF
power is being applied. Leaking RF energy is a potential health hazard.
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.
WARNING
The resistor used in this load consists of a resistive film on a special substrate.
If the substrate is broken, there will probably be sharp pieces or splinters
inside the load housing. Caution should be exercised to avoid possible injury.
CAUTION
DO NOT disconnect the water flow switch leads from the control assembly. Any
operation of the load without a properly functioning cooling system will cause
almost immediate destruction of the resistor element.

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
CONNECT INTERLOCK TO TRANSMITTER BEFORE OPERATING.
BRANCHER LE VERROUILLAGE À L'ÉMETTEUR AVANT EMPLOI.
CONECTE EL INTERBLOQUEO AL TRANSMISOR ANTES DE LA OPERACION.
VOR INBETRIEBNAHME VERRIEGELUNG AM SENDER ANSCHLIESSEN.
PRIMA DI METTERE IN FUNZIONE L'APPARECCHIO, COLLEGARE IL
DISPOSITIVO DI BLOCCO AL TRASMETTITORE.

vi
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 revi-
sion on the title page.
Literature Contents
Introduction —Describes the features of the load resistor, lists equipment sup-
plied and optional equipment, and provides power-up instructions.
Theory of Operation —Describes how the load resistor works.
Installation —Describes the power supply and load connection instructions.
Operating Instructions —Describes the base level operation instructions.
Maintenance —Lists routine maintenance tasks as well as troubleshooting for
common problems. Specifications and parts information are also included.
8745 8746

vii
Table of Contents
Safety Precautions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i
Safety Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i
Warning Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Caution Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii
Safety Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . iii
About This Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
Changes to this Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
Literature Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
Chapter 1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Purpose and Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Optional Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Direct Power Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Chapter 2 Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Heat Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Cooling Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Flow Interlock Control Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Chapter 3 Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Load Resistor Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Water Line Attachment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Cooling Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Flow Switch (Optional) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Control Box (Optional Item) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Pre-Operational Checkout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Chapter 4 Operating Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Operation as a Load Resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Operating as an RF Wattmeter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Shutting Down . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Chapter 5 Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Outside Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Preventative Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
RF Load Resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Measuring the DC Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Replacing a Resistive Element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Removing the Resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Inspecting the Unit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Replacing the Resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Replacing Fractured Resistors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Installing a Replacement Resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Removing the Front Connector Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Replacing the Water Flow Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Replacing Time Delay Relay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Replacing the Pilot Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

viii
Additional Repairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Storing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Shipping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Customer Service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Replacement Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Front Connector Parts Assigned Per Model Type: . . . . . . . . . . . . . . . . . . . 20
Model 8745 - 3-1/8" EIA Connector 50 ohms . . . . . . . . . . . . . . . . . . . . . . 20
Model 8746 - 3-1/8" Unflanged Connector
Flush Center Conductor 50 ohms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
For Both Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Optional Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Control and Water Flow Parts - not shown on Figures . . . . . . . . . . . . . . 21
Accessory Connector Kits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Model 8745 Coupling Kit -
3-1/8. Unflanged Connector Flush - 50 ohms 21. . . . . . . . . . . . . . . . . . . . . .
Limited Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

1
Chapter 1 Introduction
The Model 8745/46 Termaline Load Resistor is designed as a compact, low-
reflection, and non-radiating termination for RF transmission lines. Cooled by
internal water flow, it generates almost no surface heat, making installation
space minimal and convenient. The load can safely dissipate up to 20 kilowatts
of continuous power when used in a 50 ohm coaxial transmission line system.
Purpose and Function
Each model uses a 3-1/8 inch connector (refer to the Specifications for individ-
ual models) and will maintain a VSWR of less than 1.1 to 1.0 from 1000 Hz up
to 900 MHz. This load is intended for us-e on CW, AM, FM, SSB, and TV mod-
ulation envelopes, and within certain limitation on radar or pulse modes.
Information on applications involving pulse-type signals should be obtained
directly from Bird Electronic Corporation.
The Model 8745 and 8746 equipment consists of:
zLoad resistor
zInstruction Manual
 Note: Refer to Figure 1 on page 10 for identification of the load.
Optional Equipment
An accessory protective Control System is available as optional equipment.
When properly installed, this system protects the load by shutting off the RF
power when water flow is too low or interrupted. Discussions of the flow con-
trol pertaining to Installation and Maintenance should be ignored when not
applicable. The Models 8745 and 8746 Termaline Load Resistor has the fea-
ture of field replacement of the resistor, described in Chapter 5, Maintenance.
Direct Power Measurement
When used in conjunction with a Bird Model 4600A or 4805A Thruline Watt-
meter, these load resistors may be used for direct reading power measure-
ments up to 20 kilowatts.

Introduction
2

3
Chapter 2 Theory of Operation
General
This load resistor utilizes an external water supply for the direct cooling of the
resistor element. By using this technique, the need for an intermediate dielec-
tric fluid to transfer the heat generated in the resistor element has been elim-
inated, reducing the physical size of the load to a virtual minimum. This
simplified system allows the use of the loads in more varied environments,
and attachment in any orientation.
Heat Transfer
The 50 ohm resistor consists of a high temperature substrate tube with a
deposited resistive film. The heat generated by absorption of RF power is
transferred from the heated film to the water flowing over it, through a
restricted chamber surrounding the resistor body. This water, first diverted to
the front of the load resistor by a special inside tube, passes over the entire
length of the resistor and is discharged through the sealed water chamber at
the rear. The dielectric characteristics and distinctive design of these enclo-
sures provide a very accurate 50 ohm termination over the specified frequency
range of this load (1000 Hz to 900 MHz).
The absence of intermediate cooling fluids considerably simplifies the con-
struction and sealing of this unit. It can be readily disassembled in the field
for resistor element replacement (see “Maintenance” on page 9).
Because there is practically no heat transfer to the outer housing of the load,
the housing remains at a cool ambient temperature even under full power con-
ditions. Virtually all of the power input to the load is transformed into heat
which is carried away by the cooling water. Therefore, the differential in out-
put and input temperatures of the water, times the amount of flow, consti-
tutes an accurate gage of the power consumed by the load. The amount of this
power dissipation may be calculated from the following formula:
where:
In °F the formula is:
T2InletWaterTemperatureInCelcius=
GPM WaterFlowInGallonsPerMinute=
T1OutletWaterTemperatureInCelcius=
P PowerInKilowatts=
P0.263 T1T2
–()GPM=
P0.146 0.263()T1T2
–()GPM=
P PowerInKilowatts=
T1OutletWaterTemperatureInFahrenheit=
T2InletWaterTemperatureInFahrenheit=
GPM WaterFlowInGallonsPerMinute=
where:

Theory of Operation
4
Cooling Water
The electrical performance of these RF loads is affected by impurities or other
chemical additives in the cooling water. The presence of salts in the water defi-
nitely makes the device unusable because salts cause a rapid increase in VSWR.
Therefore, sea water or silty water should not be used for cooling the loads.
The thermal performance of these loads is also affected by impurities, particu-
larly those impurities that accumulate in the form of scale on the exposed sur-
faces of the fluid paths of the load assembly. These deposits may result in an
increase in the thermal and/or fluid resistance(s) of the load and may in turn
cause the load to overheat and fail.
The following types of water are considered safe for the cooling of the Models
8745 Load Resistor: filtered, city, or soft water. In general, any potable water
is suitable for cooling the load.
Flow Interlock Control Circuit
The interlock control circuit provides instantaneous fail-safe protection of the
transmitter and load in the event of even a momentary interruption of the
cooling water supply. This protection is necessary because dissipation of the
heat generated by the RF power absorption is critically dependent upon main-
taining the required minimum water flow rate regardless of inlet water tem-
perature.
The water flow switch, attached to the water inlet of the load, is factory cali-
brated to open the electrical contacts whenever the water flow drops below six
gallons per minute and close when the water flow exceeds this value. When
the water flow switch contacts open, the time delay relay switch is deacti-
vated, which in turn opens the interlock switch, causing immediate shutdown
of the transmitter or other signal source. The time delay relay also keeps the
interlock switch open for a preset interval of 12 ±2 seconds after the minimum
flow of six gallons per minute has been reestablished. This safeguarding fea-
ture assures proper operation of the cooling system before RF power can be
applied to the load, preventing damage or burnout of the resistor element.

5
Chapter 3 Installation
Load Resistor Connection
The compact design of the Models 8745/46 Termaline Load Resistor enables it
to be installed in very small spaces. It requires no ventilation and may be
placed at any attitude. Do not install it where the load may be subjected to
severe vibration or to physical shock.
The load is ready for connection as received from the factory. It is useful to
first check the 50 ohm input resistance of the load and record this data before
attachment (see “Maintenance” on page 9). Use the following procedure for RF
attachment.
1. Clean all conductor and insulator surfaces on the transmission line face
and, likewise, the RF input connector.
 Note: Use a dry cleaning solvent that does not leave a residue.
2. Attach the load resistor to the RF line.
 Note: Do not tighten the bolt and nut sets.
3. Use connector kits for respective models as follows:
a. Models 8745 - 3-1/8” EIA flanged, 50 ohm:
Use a 3-1/8 inch EIA coupling kit (Bird P/N 4600-020) which
includes six 3/8-16 x 1-1/2 inch bolt and nut sets, O-Ring, and
anchor bullet (center conductor).
b. Models 8746 - 3-1/8” unflanged, 50 ohm flush center conductor:
Use Bird coupling kit P/N 5-726 (RCA MI-27791K-4A) consisting of an
outer sleeve with two clamping bands and the center conductor cou-
pling bullet.
4. Rotate the load so that the warning label shows and the outlet water tube
is placed to the best advantage.
5. Secure the clamps or bolt set firmly and evenly around the RF connection.
 Note: Do not disturb the socket head cap screws that join the con-
nector section to the main housing.
Water Line Attachment
The RF Load comes supplied with standard 3/4 inch hose fittings for attaching
the water supply and drain lines. The water INLET, at the back on center and
water OUTLET, adjacent at 90°to the inlet, mate with 3/4 inch water hose con-
nectors. If the unit is supplied with the optional control system, the water flow
switch is installed on the water inlet line. See “Flow Switch (Optional)” on page 6
for alternate field installation. To connect to a rigid piping connection, replace
the water inlet and outlet hose adapters, Bird P/N 5-065-2, with ½ inch male
pipe or pipe fittings. Take special care when connecting the water lines. The
inside of the load is designed so that the water flows properly in only one direc-
tion - from the inlet to the outlet. The water flow must be kept in the proper
direction - opposite flow will cause resistor failure when power is applied.
Cooling Water Quality
Water quality is important. See “Cooling Water Quality” on page 5 for an
explanation and description. In general, any potable water is satisfactory.
This would include purified, filtered, city supply, or soft water.

Installation
6
Flow Switch (Optional)
The ports of the flow switch are 3/4 inch NPT Female. The direction of flow is
marked on the casting of the flow tube and on the operating head. Observe
carefully- opposite connection will restrict the water flow and cause load fail-
ure. The flow switch may be connected to the inlet or the outlet side of the
load, preferably as close to the load as possible. Just be certain the flow
through the switch is in the correct direction. Connect with a ½ inch NPT Nip-
ple and a ½ to 3/4 inch bushing, Bird P/N 5-489-1 and 5-490-1, or connect by
hose or pipes. In either case, the flow switch should not be over 20 feet from
the load. Alternatively, attach hose to switch with a 3/4 inch hose nipple, Bird
P/N 5-903.
Do not connect flow switch leads at this time. First turn on the water flow and
check the system for leaks and proper operation.
Control Box (Optional Item)
The wiring center and remaining elements of the control system are contained
in the control box. This includes a terminal strip and three BX cable clamps
for the input connections, a pilot lamp, and a delay timer. Only wiring mate-
rial is needed for connecting the flow switch to the control box. The control
unit operates on 115 Vac, P/N 8750-101-1, or on 230 Vac, P/N 8750-101-2,
depending on the unit ordered to suit requirements.
The pilot lamp on top of the box is a safe operation indicator; it lights only
when AC power is on and an adequate water supply is flowing. After the pilot
lamp lights up, a 12 ±2 second time delay allows sufficient time for the water
flow to stabilize before closing the transmitter interlock.
The control box is mounted by means of four 1/4 inch holes on a 5 x 5 inch
square in the back. Locate the box for the best view of the pilot light and for
easy attachment of the B.S cable and wiring. Connect the leads for each volt-
age as shown on the wiring schematic inside the control box.
 Note: These connections are critical - wire carefully.
Pre-Operational Checkout
 Note: Before attempting to operate the RF load, whether under test
or actual operating conditions, TEST the complete water system and
INTERLOCK CONTROL as follows:
1. Ensure the AC and transmitter interlock power are OFF.
2. Connect an ohmmeter across terminals six and seven (interlock).
3. Turn the AC power on.
4. Turn the water supply on.
5. Note when the water flow switch operates (audible click).
 Note: In not less than 10 seconds (12 ±2) the ohmmeter should sig-
nify a closed condition across terminals six and seven, indicating oper-
ation of the time delay switch.
6. Ensure the water flow from the OUTLET connection of the load is not less
than that given for the respective models.
 Note: As a precautionary measure, it is recommended that the pre-
operational checkout be performed each time the load is put into service.

7
Chapter 4 Operating Instructions
General
The Models 8745/46 Termaline Load Resistors do not have any operating con-
trols. Therefore, the presence of operating personnel is not required when in
use. Proper operation of the equipment is assured if the instructions contained
in "Installation" on page 5 are followed exactly.
Do not apply more than the rated RF power to the load. The water flow rates
and inlet water temperature, +5°C to 60°C (+41°F to +140°F), must be as spec-
ified in the following table.
In actuality, an adequate and uninterrupted flow of water is more critical
than the actual water temperature.
Operation as a Load Resistor
1. Turn on the AC power (if the load is equipped with an interlock system).
2. Turn on the water supply.
3. Check for proper interlock operation.
4. Check that all coaxial power line connections are properly tightened.
5. Apply RF power to the load.
6. Proceed according to instructions pertaining to the specific transmitting
equipment.
CAUTION
DO NOT disconnect the water flow switch leads from the control assembly.
Any operation of the load without a properly functioning cooling system will
cause almost immediate destruction of the resistor element.
WARNING
Never attempt to disconnect the equipment from the transmission line while
RF power is being applied. Leaking RF energy is a potential health hazard.
Model
Number
Power
Kilowatts
Min Flow Temperature
(GPM) (LPM) (°C) (°F)
8745 20 6 22.7 5 41
8746 20 8 30.3 60 140

Operating Instructions
8
Operating as an RF Wattmeter
The RF load can be combined with a Bird Rigid Line Series Thruline Wattme-
ter to form an absorption-type wattmeter by inserting the wattmeter line sec-
tion just ahead of the RF load. Installation and operation of the wattmeter is
covered in the Thruline Wattmeter Instruction Book.
 Note: Select a wattmeter type appropriate to the input connector of
the load resistor. Consult the Bird Catalog or contact the Company.
1. Perform the the same functions as a Load Resistor. See “Operation as a
Load Resistor” on page 7.
2. Rotate the element in the line section element socket to monitor incident
or reflected power.
 Note: Measurement is taken in the direction indicated by the
arrow on the element.
Shutting Down
1. Turn off the RF power to the load.
2. Wait at least one minute to allow the resistor substrate time to cool.
3. Turn the interlock and AC power off.
4. Turn off the water supply - always do this last.

9
Chapter 5 Maintenance
General
The Models 8745/46 Termaline Load Resistors are rugged and simple, requir-
ing only nominal and routine attention. The load is designed to operate satis-
factorily for long periods of time if care is taken not to exceed its power
handling capabilities.
Troubleshooting
For corrections requiring repair or replacement of components, refer to the
appropriate section for your specific model.
Cleaning
Outside Surface
The outside surface of these loads should be wiped free of dust and dirt when
necessary. The principle maintenance required by the operator will be to peri-
odically wipe the accumulated dust and lint off of the load housing. If the Tef-
lon insulator or metallic contact surfaces of the connector should become dirty
or grimy, wipe them off with a soft cloth. Use a contact cleaner that is self-dry-
ing and leaves no residue to clean the hard to reach internal portions.
 Note: Always handle the load with care to prevent subjecting it to
unnecessary shock or impact.
Inspection
With the rugged and simple construction of the loads, periodic inspection will
only be necessary at six-month intervals. Inspection should include the items
listed below:
zCleanliness - Keep the housing and connector free of grime.
zInspect the load for completeness and general condition of the equipment.
zA Troubleshooting Chart lists the commonly encountered problems,
their possible causes and remedies. Use this chart as a guide when
analyzing symptoms.
WARNING
Never attempt to disconnect the equipment from the transmission line while
RF power is being supplied. Leaking RF energy is a potential health hazard.
Problem Possible Cause Correction
Transmitter shuts off or
will not stay on.
Low water flow (for units with flow
interlock)
Increase cooling water flow.
High load VSWR. Failing resistor (resistance
change of greater than 5 ohms).
Replace resistor.
Loose input connector. Tighten conntector.

Maintenance
10
Preventative Maintenance
Due to the basic simplicity of construction, the major requirement for preven-
tive maintenance is to keep the equipment clean.
RF Load Resistor
Preparation:
zTools: Common hand tools
zOhmmeter with an accuracy of ± 1% at 50 ohms.
zUse low resistance leads, preferably a short piece of 50 ohm coaxial
cable fitted with alligator clips.
zTemperature of the load between 20°C to 25°C (68°F to 77°F)
Accurate measurement of the DC resistance between the inner and outer con-
ductors of the RF input connector will provide a good check of the condition of
the load resistor. Checking the DC resistance is simply used to measure a
change in the condition of the resistor over time. The tracking of the DC resis-
tance must start before the resistor is first put into service. Perform the follow-
ing steps and record the value for future comparison. Check and record the
resistance of the load periodically according to use.
Measuring the DC Resistance
1. Turn off RF power and interlock circuitry before any electrical disconnec-
tions are made.
2. Disconnect the RF coaxial line.
3. Connect the multimeter test leads across the center and outer conductor of
the load resistor. Refer to figure 2 for placement of the leads.
4. Record the value of the resistance before the load is put into service. Com-
pare subsequent values with the latest reading. If the values vary more
than 2 ohms this could be an indication of a failing resistive element.
 Note: These tests are by no means a necessity to the operation of
the load but merely guidelines for the users information.
 Note: It is recommended that this resistance check be performed
each time the load is to be used.
Figure 1 Measuring DC Resistance
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.