Crown FM250G Manuale utente
FM250G
Broadcast Transmitter
User’s Manual
©2002 Crown Broadcast, a division of International Radio and Electronics, Inc.
25166 Leer Drive, Elkhart, Indiana, 46514-5425 U.S.A.
(574) 262-8900
FM250G User’s Manual
ii
Revision Control
Revision Print Date
Rev A September 2002
Important Notices
©2002 International Radio and Electronics, Inc.
Portions of this document were originally copyrighted by Michael P. Axman in 1991.
A
ll rights reserved. No part of this publication may be reproduced, transmitted,
transcribed, stored in a retrieval system, or translated into any language in any form
by any means without the written permission of Crown International, Inc.
Printed in U.S.A.
Sony and RCA are trademarks of their respective companies.
IREC attempts to provide information that is accurate, complete, and useful.
Should you find inadequacies in the text, please send your comments to the
following address:
International Radio and Electronics
25166 Leer Drive, P.O. Box 2000
Elkhart, Indiana, 46515-2000 U.S.A.
Rev A
iii
Table of Contents
Section 1—Getting Acquainted
1.1 Your Transmitter ........................................................................................1–2
1.2 Applications and Options............................................................................1–3
1.2.1 Stand-Alone............................................................................................1–4
1.2.2 Backup...................................................................................................1–4
1.2.3 Booster...................................................................................................1–4
1.2.4 Exciter....................................................................................................1–4
1.2.5 Translator...............................................................................................1–5
1.2.6 Satellator................................................................................................1–6
1.2.7 Nearcasting............................................................................................1–6
1.3 Transmitter/Exciter Specifications..............................................................1–7
1.4 Receiver Specifications...............................................................................1–8
1.5 Safety Considerations.................................................................................1–9
1.5.1 Dangers..................................................................................................1–9
1.5.2 Warnings................................................................................................1–9
1.5.3 Cautions.................................................................................................1–9
Section 2—Installation
2.1 Operating Location ......................................................................................2-2
2.2 Power Connections......................................................................................2-2
2.3 Frequency (Channel) Selection....................................................................2-4
2.3.1 Modulation Compensator........................................................................2-5
2.3.2 RF Tuning Adjustments...........................................................................2-5
2.4 Receiver Frequency Selection......................................................................2-6
2.5 RF Connections ...........................................................................................2-8
2.6 Audio Input Connections .............................................................................2-9
2.7 SCA Input Connections..............................................................................2-10
2.8 Composite Input Connection.....................................................................2-10
2.9 Audio Monitor Connections.......................................................................2-11
2.10 Pre-emphasis Selection.............................................................................2-11
2.11 Processor Bypass Option ..........................................................................2-11
2.12 Program Input Fault Time-out ...................................................................2-12
2.13 Remote I/O Connector...............................................................................2-12
Section 3—Operation
3.1 FM250G Initial Power-up Procedures.........................................................3–2
3.1.1 Power Switch.........................................................................................3–3
3.1.2 Carrier Switch.........................................................................................3–3
3.2 Front Panel Bar-Dot Displays......................................................................3–4
3.2.1 Audio Processor Input............................................................................3–4
3.2.2 Highband and Wideband Display............................................................3–4
3.2.3 Modulation Display.................................................................................3–4
3.3 Input Gain Switches....................................................................................3–5
3.4 Processing Control.....................................................................................3–5
3.5 Stereo-Mono Switch...................................................................................3–5
Rev A
FM250G User’s Manual
iv
3.6 RF Output Control.......................................................................................3–6
3.7 Digital Multimeter.......................................................................................3–6
3.8 Fault Indicators...........................................................................................3–7
Section 4—Principles of Operation
4.1 Part Numbering..........................................................................................4–2
4.2 Audio Processor Circuit Board....................................................................4–2
4.3 Stereo Generator Circuit Board...................................................................4–4
4.4 RF Exciter Circuit Board..............................................................................4–5
4.5 Metering Circuit Board................................................................................4–6
4.6 Motherboard...............................................................................................4–8
4.7 Display Circuit Board..................................................................................4–8
4.8 Voltage Regulator Circuit Board..................................................................4–9
4.9 Power Regulator Circuit Board .................................................................4–10
4.10 RF Driver ..................................................................................................4–11
4.11 RF Amplifier..............................................................................................4–11
4.12 Chassis and AC Supply.............................................................................4–11
4.13 RF Output Filter & Reflectometer..............................................................4–12
4.14 Receiver Circuit Board Option...................................................................4–12
Section 5—Adjustments and Tests
5.1 Audio Processor Adjustments....................................................................5–2
5.1.1 Pre-Emphasis Selection .........................................................................5–2
5.1.2 Pre-Emphasis Fine Adjustment ..............................................................5–2
5.2 Stereo Generator Adjustments....................................................................5–2
5.2.1 Separation..............................................................................................5–2
5.2.2 Composite Output..................................................................................5–2
5.2.2.1 Using a Modulation Monitor............................................................5–2
5.2.2.2 Using Bessel Nulls...........................................................................5–3
5.2.3 19–kHz Level..........................................................................................5–3
5.2.4 19–kHz Phase.........................................................................................5–3
5.3 Frequency Synthesizer Adjustments...........................................................5–3
5.3.1 Frequency Channel Selections................................................................5–3
5.3.2 Modulation Compensator.......................................................................5–4
5.3.3 Frequency Measurement and Adjustment..............................................5–4
5.3.4 FSK Balance Control...............................................................................5–4
5.4 Metering Board Adjustments......................................................................5–4
5.4.1 Power Calibrate......................................................................................5–4
5.4.2 Power Set...............................................................................................5–4
5.4.3 SWR Calibrate........................................................................................5–5
5.4.4 PA Current Limit.....................................................................................5–5
5.5 Motherboard Adjustments..........................................................................5–5
5.6 Display Modulation Calibration...................................................................5–5
5.7 Voltage Regulator Adjustments ..................................................................5–5
5.8 Performance Verification............................................................................5–6
5.8.1 Audio Proof-of-Performance Measurements..........................................5–6
5.8.2 De-emphasis Input Network...................................................................5–6
5.9 Carrier Frequency .......................................................................................5–6
5.10 Output Power..............................................................................................5–6
Rev A
v
5.11 RF Bandwidth and RF Harmonics...............................................................5–7
5.12 Pilot Frequency...........................................................................................5–7
5.13 Audio Frequency Response ........................................................................5–7
5.14 Audio Distortion..........................................................................................5–7
5.15 Modulation Percentage...............................................................................5–7
5.16 FM and AM Noise .......................................................................................5–7
5.17 Stereo Separation.......................................................................................5–8
5.18 Crosstalk.....................................................................................................5–8
5.18.1 Main Channel Into Sub...........................................................................5–8
5.18.2 Sub Channel Into Main...........................................................................5–8
5.19 38–kHz Subcarrier Suppression.................................................................5–8
5.20 Additional Checks.......................................................................................5–8
Section 6—Reference Drawings
6.1 Views..........................................................................................................6–2
6.2 Board Layouts and Schematics ..................................................................6–4
Audio Processor.........................................................................................6–5
Stereo Generator ........................................................................................6–7
RF Exciter ...................................................................................................6–9
Metering...................................................................................................6–11
Motherboard.............................................................................................6–13
Display......................................................................................................6–15
Voltage Regulator.....................................................................................6–17
Power Regulator.......................................................................................6–19
RF Output Amplifier..................................................................................6–21
Quadrature Power Combiner ....................................................................6–22
RF Input....................................................................................................6–23
DC Input...................................................................................................6–24
RF Output Filter and Reflectometer...........................................................6–26
FM Predriver.............................................................................................6–28
Chassis Wiring..........................................................................................6–29
Receiver Board .........................................................................................6–31
Section 7—Service and Support
7.1 Service........................................................................................................7–2
7.2 24–Hour Support........................................................................................7–2
7.3 Spare Parts.................................................................................................7–2
Rev A
FM250G User’s Manual
vi
Rev A
Getting Acquainted 1—1
I
INFORMATION
Section 1—Getting Acquainted
This section provides a general description of the FM250G
transmitter and introduces you to safety conventions used within
this document. Review this material before installing or
operating the transmitter.
Rev A
FM250G User’s Manual
I
1—2
1.1 Your Transmitter
The FM250G is a member of a family of FM stereo broadcast transmitters. Crown
transmitters are known for their integration, ease-of-use, and reliability.
The integration is most apparent in the standard transmitter configuration which
incorporates audio processing, stereo generation, and RF amplification without
compromised signal quality. A single Crown transmitter can replace several pieces
of equipment in a traditional system.
Ease-of-use is apparent in the user-friendly front panel interface and in the
installation procedure. Simply select your operating frequency add an audio source,
attach an antenna, and connect AC power and you're ready to broadcast. Of course,
the FM series of transmitters also feature more sophisticated inputs and monitoring
connections if needed.
Reliability is a Crown tradition. The first Crown transmitters were designed for
rigors of worldwide and potentially portable use. The modular design, quality
components, engineering approach, and high production standards ensure stable
performance. For more direct monitoring, the front panel includes a digital
multimeter display and status indicators. Automatic control circuitry provides
protection for high VSWR as well as high current, voltage, and temperature
conditions.
Illustration 1–1 FM250G FM Broadcast Transmitter
Rev A
Getting Acquainted 1—3
1.2 Applications and Options
Crown transmitters are designed for versatility in applications. They have been used
as stand-alone and backup transmitters and in booster, translator, satellator, and
nearcast applications. The following discussion describes these applications further.
Model numbers describe the configuration of the product (which has to do with its
intended purpose) and the RF output power which you can expect.
The number portion of each name represents the maximum RF output power. The
FM250G, for example, can generate up to 250 watts of RF output power.
Suffix letters describe the configuration. The FM250GT, for example, is the standard
or transmitter configuration. Except where specified, this document describes the
transmitter configuration. In this configuration, the product includes the following
components (functions):
• audio processor
• stereo generator
• RF exciter
• metering
• low-pass filter
Illustration 1–2 Standard (Transmitter) Configuration
Stereo
Generator
Audio
Processor
Low-Pass
Filtering
Metering
RF Exciter
Rev A
FM250G User’s Manual
I
1—4
1.2.1 Stand-Alone
In the standard configuration, the FM250G is an ideal stand-alone transmitter.
When you add an audio source (monaural, L/R stereo, or composite signal), an
antenna, and AC power, the transmitter becomes a complete FM stereo broadcast
station, capable of serving a community.
As stand-alone transmitters, Crown units often replace multiple pieces of
equipment in a traditional setup (exciter, audio processor, RF amplifier).
1.2.2 Backup
In the standard configuration, Crown transmitters are also used in backup
applications. Should your primary transmitter become disabled, you can continue
to broadcast while repairs take place. In addition, the FM transmitters can replace
disabled portions of your existing system including the exciter, audio processor, or
amplifier. Transfer switches on each side of the existing and backup transmitters
make the change-over possible with minimal downtime.
1.2.3 Booster
Also in the standard configuration, Crown transmitters have been used as booster
transmitters.Boosterapplications typically involve certain geographic factorswhich
prevent your system from broadcasting to the full coverage area allowable. For
example, a mountain range might block your signal to a portion of your coverage
area. Careful placement of a Crown transmitter, operating on the same frequency as
your primary transmitter, can help you reach full coverage. An external receiver and
special antenna are required to use Crown FM transmitters as boosters.
1.2.4 Exciter
In addition to the standard configuration, Crown FM transmitters are available in
optional configurations to meet a variety of needs.
An “E” suffix, as in the FM30GE, for example, represents an exciter-only
configuration. In this configuration, the audio processor and stereo generator
boards are replaced with circuitry to bypass their function. The exciter
configurations are the least expensive way to get Crown-quality components into
your transmission system.
You might consider the Crown exciter when other portions of your system are
performing satisfactorily and you want to maximize your investment in present
equipment.
Indice
Altri manuali Crown Trasmettitore
Crown
Crown FM5 Manuale utente
Crown
Crown FM500 Manuale utente
Crown
Crown FM600 Manuale utente
Crown
Crown FM30 Manuale utente
Crown
Crown FM600 Manuale utente
Crown
Crown FM30 Manuale utente
Crown
Crown FME 20W Manuale utente
Crown
Crown FME 350W Manuale utente
Crown
Crown FMX30 Manuale utente
Crown
Crown FM10000 Manuale utente
