Linear AT71-250 User manual

Linear Industries, Inc.
AT71-250
Owner’s Manual
February 2013

AT71-250 Transmitter Owner’s Manual
© Linear Industries, Inc. All Rights Reserved 2/38
User Notices and WARNINGS
USER NOTICES
IT IS VERY IMPORTANT TO READ THIS MANUAL PRIOR TO OPERATION OF
THIS TRANSMITTER!
Notice 1
The transmitter main operating voltage setting is marked on the rear of the AT71-250
chassis.
Notice 2
The transmitter operating frequency is set from the factory.
Notice 3
For adjusting the RF output power setting a qualified technician should always employ
the use of an RF Wattmeter and a calibrated dummy load.
Notice 4
Should accident or injury occur to the personnel engaged in the installation, operation,
or service of the equipment, they should seek proper medical attention. It is advisable
that such personnel have familiarity with first-aid practices.
Notice 5
For technical support please call the Linear technical support customer service line at
847/428-5793 ext. 105.
Notice 6
The technical information presented on this manual is sole intellectual propriety of
Linear Industries, Inc. Reproduction of this document in full or partial is prohibited
without written authorization. This document is legally protected by the copyright laws.

AT71-250 Transmitter Owner’s Manual
© Linear Industries, Inc. All Rights Reserved 3/38
WARNING!
THE VOLTAGES AND CURRENTS IN THIS EQUIPMENT ARE DANGEROUS.
PERSONNEL MUST, AT ALL TIMES, OBSERVE SAFETY WARNINGS,
INSTRUCTIONS, AND ANY LOCAL REGULATIONS.
THIS OWNER’S MANUAL IS INTENDED AS A GENERAL GUIDE FOR TRAINED
AND QUALIFIED PERSONNEL WHO ARE AWARE OF THE DANGERS THAT ARE
INHERENT IN THE HANDLING AND OPERATION OF POTENTIALLY HAZARDOUS
ELECTRICAL AND ELECTRONIC CIRCUITS. IT IS NOT THE INTENT OF THIS
MANUAL TO PROVIDE A COMPLETE SET OF SAFETY INSTRUCTIONS OR
PRECAUTIONS THAT SHOULD ALREADY BE UNDERSTOOD BY TRAINED OR
EXPERIENCED PERSONNEL IN USING THIS OR OTHER TYPES AND FORMS OF
ELECTRONIC EQUIPMENT.
THE INSTALLATION, OPERATION, AND MAINTENANCE OF THIS EQUIPMENT
INVOLVE RISKS TO PERSONNEL AND ALSO TO THE EQUIPMENT. LINEAR, INC.
SHALL NOT BE RESPONSIBLE FOR INJURY OR DAMAGE THAT IS THE RESULT
OF IMPROPER PROCEDURES OR USE BY INDIVIDUALS IMPROPERLY TRAINED
OR LACKING THE KNOWLEDGE TO PERFORM ASSOCIATED TASKS.
ALL LOCAL CODES FOR BUILDING, SAFETY, FIRE, OR RELATED STANDARDS
MUST BE OBSERVED. CONSULT LOCAL AUTHORITIES FOR THE STANDARDS
FOR THE AREA OR REGION WHERE THE EQUIPMENT WILL BE INSTALLED
AND PUT IN USE.
WARNING!
AT ALL TIMES DISCONNECT AC/MAIN POWER BEFORE OPENING COVERS,
DOORS, ENCLOSURES, PANELS, OR PROTECTIVE SHIELDS THAT EXPOSE
LIVE CIRCUITS. NEVER PERFORM MAINTENANCE, MAKE ADJUSTMENTS, OR
SERVICE THE EQUIPMENT WHEN ALONE OR FATIGUED.
WARNING!
IF ELECTROLYTIC OR OIL FILLED CAPACITORS ARE UTILIZED IN THE
EQUIPMENT AND THE COMPONENT APPEARS LEAKY, OR IS BULGING, OR IF
THE CASE OR COVERING OF THE COMPONENT APPEARS DAMAGED OR
DISTRESSED, ALLOW SUFFICIENT TIME FOR THE UNIT TO COOL OR FULLY
DISCHARGE BEFORE SERVICING. SERVICING HOT OR LEAKY CAPACITORS
CAN CAUSE A RUPTURE OF THE CASE AND POSSIBLE INJURY.

AT71-250 Transmitter Owner’s Manual
© Linear Industries, Inc. All Rights Reserved 4/38
Returns and Exchanges
Equipment (Damaged or undamaged) should not be returned unless written approval
and a Merchandise Return Authorization (MRA Number) is received from your Linear
Sales representative or Linear Customer Service. Special shipping instruction will be
provided which will assure proper handling. The circumstances and reasons for the
return must be included in the request for return. Equipment that is special or
“custom” ordered may be not returnable. In situations where return or exchange is at
the request of the customer a restocking fee may be charged. All returns must be
sent freight prepaid and properly insured by customer. When communicating with
Linear please refer to your Order or Invoice Number.
Unpacking
Use care when unpacking the equipment. First perform a visual inspection of the
item(s) to determine if any damage occurred during shipment. Be sure to retain all the
shipping materials (crates and boxes or cartons) until such time that it has been
determined that the received equipment arrived undamaged. Find all PACKING
LISTS and keep them to assist in locating and identifying any components or
assemblies that may have been removed for shipping and might need to be
reinstalled in the equipment. Make sure that all shipping straps, supports and packing
materials are completely removed from the equipment prior to initialization and use.

AT71-250 Transmitter Owner’s Manual
© Linear Industries, Inc. All Rights Reserved 5/38
AT71-250 General Description
1. INTRODUCTION
AT71-250 is a 250W UHF ATSC Digital Broadcast Transmitter. It uses state-of-the-art
technology of transmission of the digital signal for TV broadcast. It carries an intelligent digital
control using microcontrollers, which allows for remote supervision in real time of all
transmitter functionality.
All operations of the AT71-250 is carried-out through a keypad and digital display, located on
the front panel, including access to all the readings, alarms and configurations.
The RF amplification system constitutes one drawer of up to 300W rms comes with an
independent power supply and supervision function. The FCC Mask filter is installed on the
top of the cabinet (not shown on the pictures below).
Figure 1: AT72-250 - Front View

AT71-250 Transmitter Owner’s Manual
© Linear Industries, Inc. All Rights Reserved 6/38
Figure 2: AT72-250 - Rear View
Figure 3 - AT71-250 - Block Diagram

AT71-250 Transmitter Owner’s Manual
© Linear Industries, Inc. All Rights Reserved 7/38
2. Main Features
Via the 4 lines x 40 columns display keypad located at the front panel it is possible to
manage, configure all functions of the equipment and each one of the RF power
drawer.
Via the hyper-terminal it is also possible to manage, configure all of the functions of
the transmitter.
Digital Filter, type Finite Impulse Power (FIR) built-in at the 8VSB Modulator.
Automatic non linear pre-correction.
Automatic linear equalization.
Built in oscillators synthesized via serial-PLL, locked at a 10MHz OCXO reference or
external equivalent reference, e.g. GPS signal.
The UHF RF power amplifier was implemented with LDMOS transistors, operating
highly linearly at higher gain under high efficiency and absolute controlled thermal
conditions.
Automatic control over the quiescent operational electrical current value on the RF
main power transistors, under temperature variations.
Self-protection against over-current on the RF main power amplifiers.
Each RF power module carries its own +50 volts full bridge type switching power
supply.
Automatic Level Control (ALC) control, which keeps the RF on-channel output level
constant, even with a +3 dB overall system gain variation.
System fault indication shown on the front panel, including current and past alarms log.
Low noise, variable speed fans for the air cooling system.
Modular design, built with SMD (Surface Mounted Devices), easing the maintenance
and service.
Outstanding overall field system performance.
19” rack cabinet.

AT71-250 Transmitter Owner’s Manual
© Linear Industries, Inc. All Rights Reserved 8/38
3. AT71-250 stage-by-stage
1. 1 Digital Exciter
2. 1 RF power drawer
3. Output FCC mask filter
4. RF Sampler
4 General Description by stage
4
4. .1 1 D Di ig gi it ta al l E Ex xc ci it te er r, , m mo od de el l A AT T8 80 00 01 1. .
The digital exciter unit is also the control and monitoring system for the entire transmitter.
8VSB Modulador
IF/UHF Up Converter
Power Supply
RF Amplifier
Master Control Unit
The AT8001 input is a single BNC connector that may receive either an ASI or SMPTE310M
transport stream. The modulation process follows ATSC A/53E recommendation, and is a
complex modulation process generating identical phase-modulated orthogonal IF carriers, (I)
and (Q) at frequency of 18.833916 MHz.
Both (I) and (Q) modulated carriers are routed into the IF/UHF up-converter. The local
oscillator is a synthesized time-based PLL via an internal OCXO (Oven Controlled Crystal
Oscillator) at 10MHz reference, or an equivalent one external reference, e.g. a GPS signal.
The on-channel modulated signal is routed to the RF amplifier, a class A highly linear
amplifier with enough head room to accommodate future signal amplitude expansion during
the non-linear pre-correction process.
The AT8001 output delivers a variable 100mW max RF output level, (+20dBm) at the desired
UHF channel, driving the RF power amplifiers line-up.
The Master Control Unit (MCU) of the unit is embedded in the AT8001. The MCU interacts
with all functionality present within the equipment. It further interfaces externally via a keypad
and an LCD display.
The MCU receives information proceeding from several modules, as the DTV modulator, Up-
Converter, RF amplifiers, RF samples and the administration of passwords. Via keypad it is
possible to read and program the power level delivered by the transmitter. Major changes on
the transmitter configuration are possible with factory assistance.

AT71-250 Transmitter Owner’s Manual
© Linear Industries, Inc. All Rights Reserved 9/38
The AT8001 is factory-set in one of four (4) optional versions. Depending upon the version it
is possible set the operation with 2 types of non-linear pre-correction, mask filter equalization
and/or ATSC set of 13 measurements on the RF signal demodulated.
4
4. .2 2 3 30 00 0 w wa at tt ts s R RF F p po ow we er r a am mp pl li if fi ie er r
The main power amplification system is built with 1 RF power drawer. The drawer carries a
set of 3 fans, switching power supply, 3 RF pallets, an intermediate power amplifier, a
removable (plug-in) control system based on microcontrollers and includes a hyper-terminal
interface.
The use of the hyper-terminal interface allows the operator to adjust the quiescent RF
transistor’s current via software. It is also possible to retrieve data information regarding RF
transistor current variations as a function of the temperature variation. Further, it is possible to
collect valuable system information related with the RF drawer serial number, embedded
software name and version, direct and reverse RF power readings, one-by-one RF transistor
current readings, and detailed descriptions about current and past alarms.
4 4. .3 3 R RF F P Po ow we er r S Se en ns so or r. . R RF F s sa am mp pl le e. .
RF samples associated with the direct and reverse RF power are detected with this unit, and
converted to proportional DC readings. These 2 DC levels are routed to the MCU located in
the exciter where they are processed and displayed on the LCD screen. The processing of
this analog information manages the RF power delivered by the transmitter, increasing or
reducing it as part of the automatic level control (ALC) and is a part of the automatic
linearization/equalization of the transmitter. The RF samples are available in two points in the
RF path (line-up), BEFORE and AFTER the RF output filter. The second set of RF samples is
the last element on the transmitter line-up, directly connected to the output transmission and
antenna system.
4
4. .4 4 O Ou ut tp pu ut t M Ma as sk k F Fi il lt te er r
The UHF RF channel output filter is a tunable band-pass six pole elliptical synthesis type filter.
This filter reduces the unwanted spurious and harmonics signals inherent in the RF
amplification process. The filter bandwidth and attenuation specifications are two important
components that help the transmitter to meet the FCC an ATSC A/53E specification
recommendation.

AT71-250 Transmitter Owner’s Manual
© Linear Industries, Inc. All Rights Reserved 10/38
4
4. .5 5 P Po ow we er r S Su up pp pl li ie es s
All power transmitter supplies are full bridge switching power supplies. Each drawer includes
a total of two power supplies, each with its own individual shut-down commands. These
power supplies are in constant communication with its respective drawer control unit. The
communication collects and distributes the voltage value (+50V nominal) and the electrical
instantaneous current values in Ampere. The normal mains value for all power supplies is
208Vac. The three different models present on this transmitter are:
5. AT71-250 - 250W UHF ATSC/8VSB Transmitter - Technical Specifications
Electrical
Main
120 VAC, bi phase, 50-60 Hz.
Consumption
1080 W
Power Factor Correction, FPC.
Included
Signal Input
Transport Stream Input
ATSC/MPEG2, compliant to SMPTE310M or
ASI
Input Data Rate
19.39 Mbps (SMPTE / 310M) / 270Mbps (ASI)
External Reference Signal
10MHz. (0 to +10 dBm).
Input Connector
75Ω (BNC),
Reference Input Connector
50Ω (BNC),
RF
Modulation Mode
8VSB.
IF
18.833916 MHz.
Channel Bandwidth
6MHz.
Test Signal
PRBS
Frequency Range
UHF. C14 to Ch59, (4 bands).
Frequency Step
1 Hz. ± 220kHz
Symbol Rate
10.76 MSymbol/sec.
Digital/Analog Converter
16 bit
Both Linear and Non-Linear Pre-Correction at factory
Included
Pilot frequency stability overall
±0.3 ppm
Peak to peak frequency response
≤ 0.2 dB
Peak to peak group delay response
≤ 20 ns.
Phase noise
≤ -104 dBc/Hz @ 20kHz offset.
Conducted spurious and harmonics
< -60 dBc, FCC 47 Part 74.
Radiated spurious and harmonics
< -80 dBc, FCC 47 Part 74.
MER (Modulation Error Rate)
≥ 33 dB (transmitter output) typical.
RF output connector
N
Output sample connector
N
Communication
Hyper-terminal
RS232 (DB-9)
Mechanical
Dimensions
7.13”(H) X 12”(W) X 9”(D)
Weight
NET: 100 lbs