AR 500T2G8 Service manual

Operating and
Service Manual
500T2G8
Model
10006896
Part Number
Serial Number
160 School House Road, Souderton, PA 18964 • 215-723-8181 • Fax [phone] • www.arworld.us

EC Declaration of Conformity
We: Amplifier Research
160 School House Road
Souderton, PA. 18964
declare that our product(s);
the Model 500T2G8 Series RF amplifiers
to which this declaration relates is in compliance with the following European directives:
Low Voltage Directive: 2014/35/EU
EMC Directive: 2014/30/EU
Supplementary Information:
Safety : EN 60215-1:1989
EN 61010-1:2010
EMC: EN 61000-6-2:2005, EN61000-6-4:2007
Year Mark Applied: 2016
I, the undersigned, hereby declare that the equipment specified above conforms to the above Directives and
Standards.
Authorized officer of the company:
James M. Maginn
President

INSTRUCTIONS FOR SAFE OPERATION
Revised 0517
Observe the following safety guidelines to help ensure your
own personal safety and to help protect your equipment and
working environment from potential damage.
INTENDED USE
This equipment is intended for general laboratory use in
generating, controlling, and measuring levels of
electromagnetic Radio Frequency (RF) energy. Ensure that the
device is operated in a location which will control the radiated
energy and will not cause injury or violate regulatory levels of
electromagnetic interference.
SAFETY SYMBOLS
These symbols may appear in your user manual or on
equipment.
This symbol is marked on the equipment when it
is necessary for the user to refer to the manual
for important safety information.
The caution symbol denotes a potential hazard.
Attention must be given to the statement to
prevent damage, destruction, or harm.
Dangerous voltages are present. Use extreme
care.
Indicates a terminal intended for connection to
an external conductor for protection against
electrical shock in case of a fault, or the terminal
of a protective earth (ground) electrode.
Indicates invisible laser radiation–do not view
directly with optical instruments.
Indicates frame or chassis ground connection
terminal.
Indicates alternating current.
Indicates this product must not be disposed of
with your other household waste.
Indicates that the marked surface and adjacent
surfaces can attain temperatures that may be hot
to the touch.
EQUIPMENT SETUP PRECAUTIONS
Review the user manual and become familiar with
all safety markings and instructions. Protection
provided by the equipment may be impaired if
used in a manner not specified by AR RF/Microwave
Instrumentation (AR).
•Follow all lifting instructions specified in this document.
•Place the equipment on a hard, level surface.
•Do not use the equipment in a wet environment, for
example, near a sink, or in a wet basement.
•Position your equipment so that the power switch is easily
accessible.
•Leave 10.2 cm (4 in) minimum of clearance on all vented
sides of the equipment to permit the airflow required for
proper ventilation. Do not restrict airflow into the
equipment by blocking any vents or air intakes.
Restricting airflow can result in damage to the equipment,
intermittent shut-downs or safety hazards.
•Keep equipment away from extremely hot or cold
temperatures to ensure that it is used within the specified
operating range.
•While installing accessories such as antennas, directional
couplers and field probes, take care to avoid any exposure
to hazardous RF levels.
•Ensure that nothing rests on your equipment’s cables and
that the cables are not located where they can be stepped
on or tripped over.
•Move equipment with care; ensure that all casters and/or
cables are firmly connected to the system. Avoid sudden
stops and uneven surfaces.
BEFORE APPLYING POWER
Your AR equipment may have more than one power supply
cable. Use only approved power cable(s). If you have not been
provided with a power cable for the equipment or for any AC-
powered option intended for the equipment, purchase a power
cable that is approved for use in your country. The power
cable must be rated for the equipment and for the voltage and
current marked on the equipment’s electrical
ratings label.
Incorrectly installing or using an incompatible line
voltage may increase the risk of fire or other
hazards. To help prevent electric shock, plug the equipment
and peripheral power cables into properly grounded electrical
outlets. These cables are equipped with three-prong plugs to
help ensure proper grounding. Do not use adapter plugs or
remove the grounding prong from a cable.
Do not modify power cables or plugs. Consult a licensed
electrician or AR trained service technician for equipment
modifications. Always follow your local/national
wiring rules.
Do not operate the equipment if there is physical
damage, missing hardware, or missing panels.
SAFETY GROUND
This equipment is provided with a protective earth
terminal. The mains power source to the equipment
must supply an uninterrupted safety ground of
sufficient size to attach wiring terminals, power
cord, or supplied power cord set. DO NOT USE this
equipment if this protection is impaired.

INSTRUCTIONS FOR SAFE OPERATION
Revised 0517
HAZARDOUS RF VOLTAGES
The RF voltages on the center pin of an RF output
connector can be hazardous. The RF output
connector should be connected to a load before AC
power is applied to the equipment. Do not come
into contact with the center pin of the RF output connector or
accessories connected to it. Place the equipment in a non-
operating condition before disconnecting or connecting the
load to the RF output connector.
ACOUSTIC LIMITATIONS
If equipment noise exceeds 80dB, ear protection is required.
MAINTENANCE CAUTION
Adjustment, maintenance, or repair of the equipment must be
performed only by qualified personnel. Hazardous energy may
be present while protective covers are removed from the
equipment even if disconnected from the power source.
Contact may result in personal injury. Replacement fuses are
required to be of specific type and current rating.
ENVIRONMENTAL CONDITIONS
Unless otherwise stated on the product specification sheet, this
equipment is designed to be safe under the following
environmental conditions:
•Indoor use
•Altitude up to 2000m
•Temperature of 5°C to 40°C
•Maximum relative humidity 80% for temperatures up to
31°C. Decreasing linearly to 50% at 40°C.
•Main supply voltage fluctuations not to exceed ± 10% of
the nominal voltage or minimum and maximum
autoranging values.
•Pollution degree 2: Normally non-conductive with
occasional condensation. While the equipment will not
cause hazardous condition over this environmental range,
its performance may vary.
EQUIPMENT CONTAINING LASERS
AR Field Probes (FL/PL Series) and Field Analyzers
(FA Series) are Class 1 laser products containing
embedded Class 4 lasers. Under normal use, the
laser radiation is completely contained within the
fiber optic cables and poses no threat of exposure. Safety
interlocks ensure that the laser is not activated unless the
cables are properly connected. Always exercise caution when
using or maintaining laser products. Do not view directly with
optical instruments.
RF ANTENNAS
•This equipment (antenna or antenna assembly) may be
heavy, requiring two persons to lift. Use caution when
installing or removing unit. Follow all equipment setup
and lifting instructions specified in this document.
•Ensure connectors are appropriate for intended operation.
Connectors are specified in the user manual and product
specification sheet.
•Do not exceed the maximum RF input level stated in the
specifications. Refer to the user manual and product
specification sheet to determine the applicable RF levels.
•Excessive RF input could damage the equipment or
connectors, causing safety hazards.
•When in operation, the RF voltages on the antenna
elements can be hazardous. Do not come into contact with
the antenna or elements when the RF input connector is
connected to a live RF source.
•To avoid injury to personnel and accidental damage to
power amplifier or antenna, disable the RF output of
power amplifier before connecting or disconnecting the
input connection to the antenna.
•Perform periodic inspections of antenna and field probe
systems to verify calibration due date, proper operation,
and overall condition of equipment.
RACK MOUNTED TWT MODELS
Some TWT models are supplied without the removable
enclosure offered for benchtop use. These rack-mountable
models may be supplied with either carry handles or slides and
front handles installed. Follow all lifting instructions specified
in this document and installation instructions supplied in the
TWT user manual.
LIFTING INSTRUCTIONS FOR AR EQUIPMENT
Because most products must be
handled during distribution,
assembly and use, the risk of serious
injury due to unsafe product handling
should be a fundamental
consideration of every user. An
authoritative guideline for eliminating unwarranted risk of
injury caused by lifting is provided by the NIOSH Work
Practices (Publication #94-110) available at:
https://www.cdc.gov/niosh/docs/94-110/pdfs/94-110.pdf.
In general, observe the following guidelines for lifting a
weight of 50 lb or more:
•Use lifting eye (for floor standing) or side handles (table
top) to lift unit only.
•Use equipment of adequate capacity to lift and support
unit.
•If using forklift to move unit, be sure forks are long
enough to extend beyond the side of the unit.
•For additional information, follow the link specified
above.

ADDITIONAL WARNINGS & NOTES
WARNING:
This equipment operates at potentially lethal voltages. Only trained,
qualified personnel should operate, maintain, or service it.
Hazardous energy may be present while protective covers are removed
from the equipment even if disconnected from the power source. Contact
may result in personal injury.
CAUTION:
Adjustment, maintenance, or repair of the equipment must be performed
only by qualified personnel.
CAUTION:
Replacement fuses are required to be of specific type and current rating.
CAUTION:
The information in this document was obtained from reliable sources and
was believed to be accurate at the time of publication. Since subsequent
modifications to the machine may have been made, use this information
only as a guide. Carefully compare the unit's actual configuration and
operation to the descriptions in this manual before you undertake to
operate, service, or modify this machine. Any variance or modification
should be noted, dated, and initialed in the discrepant part of all manuals
on hand for future reference. If you have technical or editorial comments
you wish to make to the manufacturer, please write them on photocopies
of the relevant sheets.
NOTE: The contents of this document are the property of the manufacturer and this document is delivered
on the express condition that it not be disclosed, reproduced in whole or in part, or used for
manufacture for anyone other than the manufacturer without its written consent, and that no right is
granted to disclose or so use any information in this document.

Model 500T2G8

Suggested Periodic Maintenance for TWT Amplifiers
1. Keep monthly log of the voltages, currents and temperatures as shown on Menus. Also record
Date, “Console” and “Operate” hours. Take readings in Operate mode with the gain at zero
(0%) percent. Leave unit in Operate mode for 20 minutes (Max Duty if Pulsed Unit), and then
record data. Review the log to identify trends and contact factory if required.
2. Keep monthly log of performance with active RF. At mid-band frequency, with Gain set to
100%, apply RF drive that will provide rated power. This will help indicate if the gain or power
is changing and if the traveling wave tube or pre-amp needs service. Record the following:
a. RF Drive Level
b. Forward Power
c. Reverse Power
d. Body Current (Iw)
e. Sample Port Power reading (if possible).
3. Remove air intake filter and clean using compressed air and/or vacuum cleaner.
4. Ensure air inlet and outlet are unobstructed.
5. Check that AC Input connections are secure. Make sure the AC cable is not damaged or
deteriorated.
6. Check that both input and output RF connections (waveguide or coax) are connected tightly and
un-damaged.
Rev A

TABLE OF CONTENTS
TABLE OF CONTENTS ..................................................................................................i
1. DESCRIPTION AND SPECIFICATIONS.......................................................1
1.1 TWTA Description................................................................................................1
1.2 Suggested Applications..........................................................................................1
1.3 Specifications.........................................................................................................1
1.4 Accessories............................................................................................................2
1.5 Test Data Sheet......................................................................................................2
2. THEORY OF OPERATION ..............................................................................7
2.1 Design of the amplifier..........................................................................................7
2.2 Description of the RF Circuit.................................................................................7
2.3 Description of the Power Supply...........................................................................8
3. OPERATION.......................................................................................................9
3.1 Warnings and Cautions..........................................................................................9
3.2 Installation .............................................................................................................9
3.2.1 Unpacking..............................................................................................................9
3.2.2 Mounting and Removing.....................................................................................10
3.2.3 Cooling Requirements .........................................................................................11
3.2.4 AC Line Power Connections ...............................................................................11
3.2.5 RF Output Connections .......................................................................................12
3.2.6 External Interlock Connector............................................................................... 12
3.3 Front Panel Features ............................................................................................ 14
3.4 Front Panel Display and Soft Keys......................................................................15
3.5 Rear Panel Features .............................................................................................19
3.6 Initial Turn On and Warm-up Procedure.............................................................19
3.7 Emergency Bypass Operation..............................................................................20
3.8 Remote IEEE-488 Operation...............................................................................21
3.9 TWTA General Considerations ...........................................................................26
4. MAINTENANCE...............................................................................................29
4.1 Safety Warning....................................................................................................29
4.2 Unauthorized Repairs ..........................................................................................29
4.3 Preventive Maintenance.......................................................................................29
4.4 Troubleshooting...................................................................................................30
4.5 Non-Repairable Modules.....................................................................................31
4. TECHNICAL DOCUMENTATION ...............................................................33
5.1 Top Level Build Tree...........................................................................................35
5.1.1 Three Phase..........................................................................................................35
5.1.2 Single Phase.........................................................................................................36
5.1.3 500 Watt TWT Amplifier SC-Band Single Phase AR with Sample and Input
Connectors on Front Panel...................................................................................37
5.2 Schematics........................................................................................................... 39
5.3 Parts Lists.............................................................................................................41

Model 500T2G8
5.3.1 Parts List, HPA Logic and Control Module, A16485-000 .................................42
5.3.2 Parts List, Power Supply for TWT 5196/5296 , 3 A22826-500..........................44
5.3.3 Parts List, Power Supply for TWT 5196 /5296 , 1 A22826-501.........................45
5.3.4 Parts List, Emergency Bypass Board, A24830-001.............................................46
5.3.5 Parts List, HPA Interface Board (Plastic) A25444-000.......................................47
5.3.6 Parts List, Microwave Power Assy for 500T SC, A26857-003........................... 50
5.3.7 Parts List, 500W TWT Amplifier, SC-Band, Single, A26901-311.....................51
5.3.8 Parts List, 500W TWT Amplifier, SC-Band, Three, A26901-313...................... 52
5.4 Sample Program for IEEE-488 Communication .................................................53
FIGURES
3-1 Side View of TWT showing Threaded Holes......................................................10
3-2 Front Panel Features ............................................................................................14
3-3 Front Panel Display Screens................................................................................15
3-4 Rear Panel Features .............................................................................................19
TABLES
3-1 Front Panel Features ............................................................................................14
3-2 Rear Panel Features .............................................................................................19
3-3 Catalog of IEEE-488 Commands.........................................................................21
3-4 Catalog of Status Codes.......................................................................................23
3-5 Catalog of Fault Codes ........................................................................................23
3-6 Catalog of System State Codes............................................................................ 24
3-7 *STA?; Response Codes......................................................................................24
3-8 *STB?; Response Codes......................................................................................25
3-9 Catalog of Heater Auto Off Time Delay Codes...................................................25

Rev E 1
1. DESCRIPTION AND SPECIFICATIONS
This manual provides operating, interfacing and selected service information pertinent to AR
RF/Microwave Instrumentation Model 500T2G8 Broadband Microwave Amplifier. The Model
500T2G8 is a 500 watt S/C band traveling-wave tube amplifier (TWTA). This manual supports models
offering three phase and single phase operation, as well models offering additional special features.
Refer to the model specification sheet to determine the applicable features of this unit.
1.1 TWTA DESCRIPTION
The amplifier uses a broadband traveling-wave tube (TWT) to provide 500 watts minimum output over the
TWT amplifier's full bandwidth. The amplifier is well suited for susceptibility and general laboratory testing
where instantaneous bandwidth and high gain are required.
The amplifier is completely self-contained and packaged for standard 19-inch rack mounting. The front panel
of the rack mountable amplifier is 8.75 inches high, and the overall unit is 25.25 inches deep, excluding the
rear-panel connectors. For bench top use, the amplifier is supplied in an enclosure with integral carrying
handles.
Primary power is 208 volts (±10%) 50/60 Hz., three-phase, five-wire or alternatively depending upon Model
190-260VAC single-phase 50/60 Hz. An efficient switching power supply design provides minimum power
consumption. In addition, the dual collector TWT is designed to minimize prime power consumption at low
RF output levels. A fast regulation control loop and a high degree of filtering ensure performance within
specifications over a wide range of operating conditions. The amplifier is fully enclosed, and the upper and
lower panels of the rack mountable amplifier enclosure are interlocked to reduce the likelihood of accidental
contact with high voltage.
1.2 SUGGESTED APPLICATIONS
•RF Susceptibility testing
•Antenna and component testing
•Equipment calibration
•General laboratory instrumentation
1.3 SPECIFICATIONS
Refer to the AR Data Sheet on the following pages for detailed specifications.

Model 500T2G8
2 Rev E
1.4 ACCESSORIES
AR RF/Microwave Instrumentation offers a number of accessories for use with this amplifier including:
•Directional coupler
•Antenna
•Flexible transmission line
Refer to a current AR RF/Microwave Instrumentation catalog for Microwave Accessories.
1.5 TEST DATA SHEET
A Test Data Sheet for a specific unit is prepared at the time of manufacture and is included with the unit's
copy of this manual.

perature. Modular design of the power supply
and RF components allow for easy access and
repair. Use of a switching mode power supply
results in significant weight reduction.
Housed in a stylish contemporary cabinet, this
unit is designed for benchtop use, but can be
removed from the cabinet for rack mounting.
The Model 500T2G8 provides readily available
RF power for a variety of applications in Test and
Measurement, (including EMC RF susceptibility
testing), Industrial and University Research and
Development, and Service applications.
See model configuration for primary power,
alternative packaging and special features.
The export classification for this equipment is
EAR99. These commodities, technology or soft-
ware are controlled for export in accordance
with the U.S. Export Administration Regulations.
Diversion contrary to U.S. law is prohibited.
The Model 500T2G8 is a self-contained, forced
air cooled, broadband traveling wave tube
(TWT) microwave amplifier designed for applica-
tions where instantaneous bandwidth and high
gain are required. A reliable TWT provides a
conservative 500 watts minimum at the amplifier
output connector. Stated power specifications
are at fundamental frequency.
The amplifier's front panel digital display shows
forward and reflected output plus extensive sys-
tem status information accessed through a series
of menus via soft keys. Status indicators include
power on, warm-up, standby, operate, faults,
excess reflected power warning and remote.
Standard features include a built-in IEEE-488
(GPIB) interface, 0dBm input, VSWR protection,
gain control, RF output sample port, auto sleep,
plus monitoring of TWT helix current, cathode
voltage, collector voltage, heater current, heater
voltage, baseplate temperature and cabinet tem-
Features
Specifications
500T2G8
 M2–M98
 500 Watts CW
 2.5GHz–7.5GHz
AR RF/Microwave
Instrumentation
160 School House Rd
Souderton, PA 18964
215-723-8181
For an applications engi-
neer call:800.933.8181
www.arworld.us

POWER (fundamental), CW, @ Output Connector:
Nominal 541 watts
Minimum 500 watts
Linear @ 1 dB Compression 125 watts minimum
FLATNESS: ±8 dB maximum, equalized for ±5 dB
maximum at rated power
FREQUENCY RESPONSE: 2.5–7.5 GHz instantaneous-
ly
INPUT FOR RATED OUTPUT: 1.0 milliwatt maximum
GAIN (at maximum setting): 57 dB minimum
GAIN ADJUSTMENT (continuous range): 35 dB mini-
mum
INPUT IMPEDANCE: 50 ohms, VSWR 2.0:1 maximum
OUTPUT IMPEDANCE: 50 ohms, VSWR 2.5:1 typical
MISMATCH TOLERANCE: Output power foldback
protection at reflected power exceeding 100 watts. Will
operate without damage or oscillation with any magni-
tude and phase of source and load impedance. May
oscillate with unshielded open due to coupling to in-
put. Should not be tested with connector off.
MODULATION CAPABLITY: Will faithfully reproduce
AM, FM, or pulse modulation appearing on the input
signal. AM peak envelope power limited to specified
power.
NOISE POWER DENSITY: Minus 85 dBm/Hz
(maximum); Minus 95 dBm/Hz (typical)
HARMONIC DISTORTION: Minus 3dBc maximum;
Minus 3.5dBc typical
CONNECTORS:
RF input: Type N female, rear
RF output: 7-16 DIN female, rear
RF output sample port: Type N female, rear
GPIB: IEEE–488 (f), rear
Interlock: DB-15 (f), rear
COOLING: Forced air (self contained fans), air entry
and exit in rear.
WEIGHT AND SIZE: See Model Configurations
EXPORT CLASSIFICATION: EAR99
Page 2
Specifications
500T2G8
 M2–M98
 500 Watts CW
 2.5GHz–7.5GHz
EMust select one enclosure type from the follow-
ing [E1 or E2 or E2S]:
E1 removable outer enclosure, size 20 x 10 x 27 in.,
50.8 x 25.4 x 68.6 cm; add 14 kg (30 lbs) to
weight of E2.
E2 without outer enclosure, size 20 x 8.75 x 26 in,
50.8 x 22.2 x 66.1 cm; weight 41 kg (90 lbs).
E2S enclosure removed for rack mounting; slides and
handles installed, size 20 x 8.75 x 26 in, 50.8 x
22.2 x 66.1 cm; add 2 kg (5 lbs) to weight of
E2.
PMust select one primary power from the follow-
ing [P1 or P2]
P1 208 VAC ± 10% three phase 50/60 Hz 3.5 KVA
maximum
P2 190-260 VAC single phase 50/60 Hz 3.5 KVA
maximum
Model Configurations
S May select a special feature (extra cost) from the
following [{S3V or (S1R and/or S4P and/or
S5V}):
S1R Reflected power port, type N female connector
on rear panel. Forward and reflected sample
port calibration data supplied on disk in Excel
format at 51 points, evenly spaced over specified
frequency response.
S3V Shipped without outer cabinet, flatness ± 3 dB
max at rated power, and a video pulse capability
to offer blanking capability to use for noise qui-
eting. See Video Pulse Capability table below.
S4P Power minimum 650 watts from 3.0 GHz to 3.6
GHz.
S5V Video pulse capability to offer blanking capabil-
ity to use for noise quieting. See Video Pulse
Capability table below.
S5V & S3V - VIDEO PULSE CAPABILITY
Pulse Width: 0.05 microseconds min
Pulse Rate (PRF): 100 kHz max
RF Rise and Fall: 30 ns max (10% to 90%)
Delay: 300 ns max from pulse input to RF90%
Pulse width distortion: ±30 ns max (50% points of output pulse width compared to 50%
points of input pulse width)
Noise Power Density, (pulse off): Minus 140 dBm/Hz (typical)
Connector, Video: BNC-female on rear panel

Page 3
500T2G8
 M2–M98
 500 Watts CW
 2.5GHz–7.5GHz
Model Configurations
To order AR Products, call 215.723.8181. For an applications engineer call:800.933.8181. Direct to Service call: 215.723.0275 or
email: [email protected] For Faxing Orders:866.859.0582 (Orders Only Please) [email protected]
Approved for public release by AR RF/Microwave Instrumentation 081417
Model Features Model Features Model Features
EPSEPSEPS
500T2G8 E1 P1 -M32 E1 P1 S1R & S4P M77 E1 P2 S4P & S5V
M2 E2 P1 -M33 E2 P1 S1R & S4P M78 E2 P2 S4P & S5V
M3 E1 P2 -M34 E2S P1 S1R & S4P M79 E2S P2 S4P & S5V
M4 E2 P2 -M35 E1 P2 S1R & S4P M80 E1 P1 S1R & S4P & S5V
M5 E2S P1 -M36 E2 P2 S1R & S4P M81 E2 P1 S1R & S4P & S5V
M6 E2S P2 -M37 E2S P2 S1R & S4P M82 E2S P1 S1R & S4P & S5V
M7 E2 P2 S3V M50 E1 P1 S5V M83 E1 P2 S1R & S4P & S5V
M8 E2S P2 S3V
M51 E2 P1 S5V M84 E2 P2 S1R & S4P & S5V
M11 E1 P1 S1R M52 E2S P1 S5V M85 E2S P2 S1R & S4P & S5V
M12 E2 P1 S1R M53 E1 P2 S5V M98
M13 E1 P2 S1R M54 E2 P2 S5V
M14 E2 P2 S1R M55 E2S P2 S5V
M15 E2S P1 S1R M56 E1 P1 S1R & S5V
M16 E2S P2 S1R M57 E2 P1 S1R & S5V
M25 E2S P2 M58 E2S P1 S1R & S5V
M26 E1 P1 S4P M59 E1 P2 S1R & S5V
M27 E2 P1 S4P M60 E2 P2 S1R & S5V
M28 E2S P1 S4P M61 E2S P2 S1R & S5V
M29 E1 P2 S4P M74 E1 P1 S4P & S5V
M30 E2 P2 S4P M75 E2 P1 S4P & S5V
M31 E2S P2 S4P M76 E2S P1 S4P & S5V
See Individual Specification Sheet

Rev E 7
2. THEORY OF OPERATION
2.1 DESIGN OF THE AMPLIFIER
The Model 500T2G8 TWT amplifier consists of four principal subsystems. Two of these subsystems, the
microwave power assembly and the TWT power supply are discussed in Sections 2.2 and 2.3, respectively.
The other two subsystems are the microprocessor control system and the TWTA packaging. These both
consist of a number of subassemblies. See the build tree in Section 5.1 for further information about how the
parts lists are structured.
The heart of the microprocessor control system is the control head assembly (A22933-300), which consists of
the CPU board (A18450-006) and the data link board (A22488-001). The microprocessor control system
supervises the power supply, provides metering display, processes operator front panel inputs, and enables
communication with a host computer over the IEEE-488 interface. Communication from the front panel is
through the HPA display board (A22700-900).
The control head is provided with its own power supply and, other than thru the IEEE-488 interface bus, is
electrically isolated from the amplifier. Communication with the amplifier is via fiberoptic links to the HPA
interface assembly (A25444-000).
The TWTA packaging consists of cabinet assembly (A26858-001). The cooling system utilizes a 400 Hz.
high-speed tubeaxial blower with a dedicated power supply.
2.2 DESCRIPTION OF THE RF CIRCUIT
The TWTA consists of two stages of RF amplification: a solid-state preamp assembly with adjustable gain
(E01136-000) and a traveling-wave tube amplifier (E08072-000).
The Type N RF input connector is located on the rear panel. The RF input is fed to the input connector on the
solid-state preamp. The solid-state preamp's output drives the RF input of the TWT via an equalizer. The RF
output of the TWT is a Type S-C coaxial connector. The output is directed through a short cable to a -40/-30
dB dual directional coupler. The output 7-16 DIN connector of the coupler protrudes through the rear panel of
the TWTA to function as the RF output connector.
The reflected port output of the dual directional coupler is split by a -10 dB coupler. The direct output is
connected to a detector diode, whose output is used for VSWR protection by the power supply logic board,
for VSWR measurement in the leveling loop, and for reflected power measurement on the HPA interface
board. The side port of this -10 dB coupler provides a reflected RF sample at a Type N connector on the rear
panel.
The forward port output of the dual directional coupler is split by a -10 dB coupler. The direct output is
connected to a detector diode via a pad. The output of the detector diode is used on the HPA interface board
to measure forward power, and for providing output level input to the automatic forward power limiting
circuit. The side port of this coupler is connected to the forward Type N RF sample port on the rear panel.
Amplifier gain is determined by the solid-state amplifier (SSA), which has a voltage-controlled variable gain
stage. The control head determines the output of a digital-to-analog converter (DAC) on the HPA interface
board. The output of the DAC controls the SSA gain. The emergency bypass board (A24830-001) is mounted
behind the front panel. It is provided with a circuit that increases the attenuation so that reflected power is
limited to a level that can be safely sustained without damage to the amplifier (on the order of 100 watts).

Model 500T2G8
8 Rev E
emergency bypass operation (see Section 3.7) the gain control signal is provided locally by means of a
potentiometer on the emergency bypass board. However, the foldback circuit remains on line in emergency
bypass operation.
2.3 DESCRIPTION OF THE POWER SUPPLY
The single phase version (A22525-311) is described. The TWT power supply is of modular construction. Low
voltage power for logic and control of the entire power supply assembly is provided by the low voltage power
supply module (A23687-001). In addition this module provides DC power for the HPA interface and
emergency bypass board. Control logic and TWT protection circuits are contained in the HPA logic and
Control Assembly (A16485-000).
The Heater Power Supply Module (A10010-000) powers the TWT DC heater. Grid bias and pulse top are
provided by the Grid Modulator Module (A21422-000).
The high voltage power supply consists of the following: the power factor module (A23683-000) converts
line voltage to DC for the high voltage switching supply. Switching transistors are on the Power Board
Assembly (A23719-000), and switching is controlled by the Pulse Width Modulation (PWM) Board
(A10017-511). The high voltage transformer and rectifiers are contained in the High Voltage Diode/Cap
Assembly (A21425-296). The high voltage DC is filtered in the HV Filter Assembly (A21461-500).
Low voltage interconnects between the power supply modules are through a motherboard. It is installed in a
finned heat sink assembly to which the modules are bolted. The heat sink is cooled by the incoming cabinet
air. The Heat Sink/Motherboard assembly is A23280-000.