Linear AT71-250 Manuale utente

Linear Industries, Inc.

AT71-250

Owner’s Manual

February 2013

AT71-250 Transmitter Owner’s Manual

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

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

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

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

Figure 2: AT72-250 - Rear View

Figure 3 - AT71-250 - Block Diagram

AT71-250 Transmitter Owner’s Manual

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

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

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

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.

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.

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.

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

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),

Modulation Mode

8VSB.

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

Output sample connector

Communication

Hyper-terminal

RS232 (DB-9)

Mechanical

Dimensions

7.13”(H) X 12”(W) X 9”(D)

Weight

NET: 100 lbs

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