Transamerica Broadcasting EM250DIG 250 Watt FM Broadcast Transmitter User Manual manual ING v1 1 EM 250CD
Transamerica International Broadcasting Inc 250 Watt FM Broadcast Transmitter manual ING v1 1 EM 250CD
Contents
- 1. User Manual Part 1
- 2. user Manual Part 2
User Manual Part 1
TECHNICAL MANUAL
v1.1 February 2006
SISTEMAS ELECTRONICOS S.A.
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OMB EUROPE:
Factory: Camino de los Albares,14 -Ph. 976.50.35.80, Fax: 976.50.38.55 – 50410 CUARTE DE HUERVA (Zaragoza) ESPAÑA
Sales Dpt.: Avda. San Antonio,41– Ph. 976.50.46.96, Fax: 976.46.31.70 – 50410 CUARTE DE HUERVA (Zaragoza) ESPAÑA
E-mail: europa@omb.com
Web: www.omb.es
OMB USA:
3100 NW 72nd. Avenue Unit 112 – MIAMI, Florida 33122 – Ph.: 305 477-0973, 305 477-0974, Fax: 305 477-0611
E-mail: usa@omb.com
Web: www.omb.com
OMB ESPAÑA
Av. San Antonio, 41
50410 Cuarte de Huerva
ZARAGOZA (ESPAÑA)
Website: http://www.omb.com
e-mail: europa@omb.com
Tlf: + 34 976 50 46 96
Fax: + 34 976 46 31 70
SISTEMAS ELECTRÓNICO
S
Nº Es01-022 Nº Es01-E021
LIMITED WARRANTY
About Installation_____________________________________________________________
1. - Mains Voltage must be kept between ±10% about its nominal value, unless otherwise
specified. If were variations exceeding this tolerance, it will be indispensable to install a voltage
stabilizer system within station. If transient overvoltages, due to electric motors, or other devices
of this sort connected to the distribution line, were present, or if the distribution line is exposed
to atmospheric electrical discharges, it must be indispensable the installation of isolation
transformers and gaseous dischargers before connecting any equipment within station.
2. - All equipments must be connected to station ground system in order to avoid damage
both to equipments and maintenance personnel too. It is necessary to connect a differential
automatic switch (lifesaver) at station.
3. - Some equipments does not include interlock protection for open doors, covers or
connectors. In that case, these equipments must be kept in key –locked places, with access
only to conveniently qualified personnel that is previously noticed about not to open doors,
covers or connectors without disconnecting station mains switch before performing this job.
4. - Transmitter equipments NEVER will be operated with output powers over its nominal values,
or with signals or input informations others than those specified in its individual characteristics.
5. - Ambient temperature inside equipments' room, will accomplish technical specifications of
equipments installed at station lodge. In absence of such specifications, maximum allowable
temperatures will be from -5 to + 45ºC for Television equipments, and from 0 to + 40ºC for
Sound Broadcast equipments.
6. - In case of operation at abnormally high or extremely high temperatures (over 30 to 40 º
C), it is obligatory to install a forced cooling system that will keep temperature below its upper
limit. In case of operation at abnormally or extremely low temperatures, it will be obligatory to
install a thermostatic controlled heating system for equipment's room.
7. - Both equipment's surroundings and room must be free of dust and dirt. Ambient relative
humidity will be kept below equipment's extreme specifications. In case of absence of this
specification, allowable maximum will be 90 % of relative humidity, non-condensing. Average
relative humidity will be kept under 70%, non-condensing.
8. - Every transmission equipment that can radiate some quantity of RF power, must be
connected to a load or antenna system, suited to its individual specifications , before being
energized.
9. - Maximum allowable VSWR in antenna systems both for Television or FM Radio Broadcast
operation of a given transmitter, will be 1.25:1, unless otherwise specified.
10.- For those transmitter equipments having power valve amplifiers, and that doesn't has an
automatic shutoff cycle, and must be manually turned off, as a first step high voltage, or
anode voltage, will be disconnected, keeping forced cooling system working during at least 5
minutes after high voltage disconnection, and only after this time, cooling system & filament
voltage can be shutted off. O.M.B. Sistemas Electrónicos, S.A., is not responsible of damages
to those power valves caused by sudden AC mains failures at station where our equipments
are installed.
11.- Periodically, monthly as a maximum, technical personnel must visit station in order to
perform a general equipment maintenance, unless otherwise specified. This maintenance will
include output power check, VSWR of antenna systems, forced cooling or heating systems
checks, both for equipments and station itself, including air filters cleaning, measuring of
transmission frequency with eventual correction if necessary, and will perform a general check
of fundamental parameters of equipments. In the event of any important change in some
operation parameter, that will require replacement or readjustment of any unit, Customer
MUST CONTACT FIRST WITH O.M.B. SISTEMAS ELECTRONICOS, S.A. BEFORE ANY ATTEMPT TO
READJUST OR REPLACE ANY COMPONENT OR UNIT INSIDE EQUIPMENTS, IN ORDER TO KEEP
VALID THIS WARRANTY.
12.- For equipments who are located in fixed racks or cabinets, those equipments must be
effectively connected, according to International Installations Standards, to station ground
system, whose total impedance measured to ground can't be higher than 5 ohms.
Equipments must be connected to ground system so that they can be kept out of main
discharge path between tower and ground.
About Transportation___________________________________________________________
1. - O.M.B. Sistemas Electrónicos, S.A. is not responsible of damages and/or detriments derived
from mishandling, steal, robbery, theft or vandalism during the act of transportation of
equipments to final or intermediate destination.
About Storage________________________________________________________________
1. - O.M.B. Sistemas Electrónicos, S.A. is not responsible of damages and/or detriments derived
from unappropiate storage of equipments, within inadequate warehouses or outdoors, once
equipments are delivered to transportist agency.
About Projects________________________________________________________________
1.- O.M.B. Sistemas Electronicos, S.A. is not responsible of inadequate use of equipments
made or registered by our Company, accomplishing propagation projects that are not
performed by our Specialists.
About Systems________________________________________________________________
1.- O.M.B. Sistemas Electrónicos, S.A. is not responsible for performance of those equipments
or systems that are not made, certified or registered by our Company.
About Operation______________________________________________________________
1.- O.M.B. Sistemas Electrónicos, S.A. is not responsible of damages and/or detriments derived
from inadequate or negligent operation of equipments made, certified or registered by our
Company, once those equipments are operated by personnel hired and/or employed by
Customer.
General______________________________________________________________________
This Warranty covers and protects, during a period of 18 months after start of operations, all
equipments made , certified or registered by O.M.B. Sistemas Electrónicos, S.A., including its
components and units, against failures in workmanship that may occur during operation of
those equipments, with the exception of power valves or semiconductor devices that are
covered by its particular Factory's Guarantee. In this case, O.M.B. Sistemas Electrónicos, S.A.
only can act as intermediary for negotiation with such Factory, about accomplishment of
individual Guarantees.
For Validity of this Warranty, it is indispensable that all Paragraphs be respected by the
Customer. Otherwise, this Warranty will be automatically voided. This Warranty is self-activated
with the reception by OMB Sistemas Electrónicos, S.A. of the "Guarantee Activation Manual"
returned to OMB by Customer. If such Document is not received, this Warranty will be
voided.
All repairings or adjustments covered by this Warranty are free of workmanship & materials
costs and expenses, but postage and transportation expenses of equipments and O.M.B.
technical personnel & specialists, if required, will be carried out by the Customer.
O.M.B. Sistemas Electrónicos, S.A.
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 1
LIST OF CONTENTS
SECTION 0. GENERAL RECOMMENDATIONS 2
Gives information on safety procedures and good practices to use the equipment.
SECTION 1. GENERAL DESCRIPTION 6
Introduction to the manual, technical specifications and description of the equipment’s features.
SECTION 2. DESCRIPTION OF INTERNAL MODULES 14
Contains a deep description of the system operation, including lists of components, schematics and
layouts.
SECTION 3. INSTALLATION AND MAINTENANCE 53
Contains basic instructions for unpacking and installing the equipment and recommended maintenance
operations for a good system operation.
SECTION 4. SETTINGS 63
Instructions to configure the equipment by using the software installed.
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 2
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Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 3
GENERAL SAFETY RECOMMENDATIONS
When connecting the equipment to the Mains power, please follow these important
recommendations:
This product is intended to operate from a power source that will not apply more than 10% of
the voltage specified on the rear panel between the supply conductors or between either supply
conductor and ground. A protective-ground connection by means of the grounding conductor in
the power cord is essential for a safe operation.
This equipment is also grounded through the grounding conductor of the power cord. To avoid
electrical shock, plug the power cord into a properly wired socket before connecting to the
product input or output terminals.
Upon loss of the protective-ground connection, all accessible conductive parts (including parts
that may appear to be insulated) can render an electric shock. Equipment must be connected
to station's ground system before any attempt to connect it to Mains electrical supply.
To avoid fire hazard, use only fuses of the type, voltage rating, and current rating specified in this
manual. For fuse replacement, always refer to User’s Manual.
To avoid explosion, do not operate this equipment in an explosive atmosphere.
To avoid personal injury, do not remove the product covers or panels. Do not operate the
product without the covers and panels properly installed.
GOOD PRACTICES
During the maintenance of the equipment covered in this Manual, please keep in mind the following
standard good practices:
When connecting any instrument (wattmeter, spectrum analyzer, etc.) to a high frequency output,
use the appropriate attenuator or dummy load to protect the final amplifiers and the instrument input.
When inserting or removing printed circuit boards (PCBs), cable connectors, or fuses, always turn off
power from the affected part of the equipment. After power is removed, allow sufficient time for the
capacitors to bleed down before reinserting PCBs. Always use discharge stick when available.
When troubleshooting, remember that FETs and other metal-oxide-semiconductor (MOS) devices
may appear defective because of leakage between traces or component leads on the printed circuit
board. Clean the printed circuit board and recheck the MOS device before assuming it is defective.
When replacing MOS devices, follow standard practices to avoid damage caused by static charges
and soldering.
When removing components from PCBs (particularly ICs), use care to avoid damaging PCB traces.
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 4
FIRST AID IN CASE OF ELECTRICAL SHOCK
If someone seems unable to free himself while receiving an electric shock, turn power off before
rendering aid. A muscular spasm or unconsciousness can make a victim unable to free himself from
the electrical power.
If power cannot be turned off immediately, very carefully loop a length of dry non-conducting
material (such as a rope, insulating material, or clothing) around the victim and pull him free of the
power. Carefully avoid touching him or his clothing until free of power.
EMERGENCY RESUSCITATION TECHNIQUE
Step 1
Check the victim for unresponsiveness. If there is no response, immediately call
for medical assistance, and then return to the person.
Step 2
Position the person flat on their back. Kneel by their side and place one hand on
the forehead and the other under the chin. Tilt the head back and lift the chin
until teeth almost touch. Look and listen for breathing.
Step 3
If not breathing normally, pinch the nose and cover the mouth with yours. Give
two full breaths. The person's chest will rise if you are giving enough air.
Step 4
Put the fingertips of your hand on the Adam's apple, slide them into the groove
next to the windpipe. Feel for a pulse. If you can not feel a pulse or are unsure,
move on to the next step.
DO NOT TOUCH VICTIM OR HIS CLOTHING
BEFORE POWER IS DISCONNECTED OR YOU
CAN ALSO BECOME A SHOCK VICTIM
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 5
Step 5
Position your hands in the center of the chest between the nipples. Place one
hand on top of the other.
Step 6
Push down firmly two inches. Push on chest 15 times.
CONTINUE WITH 2 BREATHS AND 15 PUMPS UNTIL HELP ARRIVES.
TREATMENT FOR BURNS
Continue treating victim for electrical shock.
Check for points of entry and exit of current.
Cover burned surface with a clean dressing.
Remove all clothing from the injured area, but cut around any clothing that adheres to the skin
and leave it in place. Keep the patient covered, except the injured part, since there is a tendency to
chill.
Splint all fractures. (Violent muscle contractions caused by the electricity may result in fractures.)
Never allow burned surfaces to be in contact with each other, such as: areas between the fingers or
toes, the ears and the side of the head, the undersurface of the arm and the chest wall, the folds of
the groin, and similar places.
Transport the victim as soon as possible to a medical facility.
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 6
CONTE
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1.1 Introduction . . . . . . . . . . . . . . . . . . 7
1.2 Description . . . . . . . . . . . . . . . . . . . 7
1.3 Front panel . . . . . . . . . . . . . . . . . . . 9
1.4 Rear panel . . . . . . . . . . . . . . . . . . . 11
1.5 Inner layout . . . . . . . . . . . . . . . . . . . 12
1.6 Technical specifications . . . . . . . . . . . . 13
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FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 7
1.1 Introduction.
The OMB EM-250 COMPACT DIG series transmitters are the result of experience gained by OMB during
years of producing FM broadcast equipment, transmitters, stl and stereo encoders. These transmitters
were specifically designed to comply with the latest international standards and the requirements of
advanced broadcasters,meeting tighter specifications than usually required,at an affordable cost.
Great care went into producing a Hi-Fi-quality modulated signal,with low residual noise and
distortion.The RF signal is also free from spurious and harmonic components to a higher degree than
required by CCIR, European, USA and most other national standards.To obtain this outstanding
performance, OMB strongly recommend to rely on qualified personnel to install and verify the
equipment which makes up the radio station, i.e.the transmitter, the possible stl and power amplifier,
the corresponding antennas,cables and connectors.This will assure to achieve the best performance
and stability in time. To this aim,OMB especially recommend that their equipment should not be
tampered with by unskilled personnel and its after-sale service is available to customers for any
technical problem.Before proceeding to installation, please carefully read at least the general
installation part of this manual, to gain confidence with the equipment.
The EM-250 COMPACT DIG transmitters are very stable and changes to the internal pre-setting other
than frequency and few other options are not usually required but, if they are, once again they must
be done by skilled personnel, fitted with proper instrumentation and service documentation.
Improperly tampering with the settings may harm the apparatus or jeopardize the guaranteed
performance.
THIS EQUIPMENT COMPLIES WITH ALL RELEVANT EMI /EMC AND SAFETY REQUIREMENTS, ETSI EN300384,
ETS300447 AND EN60215 STANDARDS.
NO INTERNAL ADJUSTMENT OR PRESETTING IS REQUIRED DURING NORMAL OPERATION.EQUIPMENT SHALL
BE PROPERLY GROUNDED AND BE OPERATED WITH ALL THE COVERS CLOSED TO PREVENT ELECTRICAL
HAZARDS AND COMPLY WITH EMC STANDARDS.
OMB hence recommends for these equipments not to be handled by unskilled personnel,together
with antenna system, transmission lines and the remaining components, both at Transmitters and
related equipments and station's antennas system.
A good installation,made by skilled and trained personnel will avoid many future troubles during
station's exploitation process. All the operations described in the Certification of Limited Warranty must
be accomplished to have the right of make any claim concerning this Warranty,having free
equipment service by OMB's technical personnel during this first exploitaition phase of Equipment.
1.2 Description.
The EM-250 COMPACT DIG is a 250W rated, direct-synthesis, FM-modulated transmitter. Being digitally
controlled, it is extensively put on the air on field by front panel or remotely in additional aspects:
frequency, power, channel sensitivity, preemphasis, functioning mode (mono, stereo, external mpx),
clock and date and many other parameters without adjusting or substituting any part. A powerful 3-
level password management permits a very high degree of security and privacy as may be required
in different situations. Equipment requires little o no maintenance and its simple modular layout
facilitates stage testing and servicing.
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 8
Fig. 1-1: THE EM-250 COMPACT DIG DIGITALLY-CONTROLLED F.M. TRANSMITTER
As imposed by various national standards, these transmitters incorporate sophisticated low-pass audio
filters on mono and stereo channels,and a sharp acting modulation limiter, which is usually set at a
peak deviation slightly higher than 75kHz. Its intervention may nevertheless be avoided, if required, pre-
setting its threshold at a deviation higher than 150kHz. Output frequency is phase-locked to a
temperature-compensated crystal oscillator,which ensures superior precision and stability. A very low
noise,low distortion VCO produces a harmonic-free, spurious-free signal. A lock control circuit inhibits
the presence of power on the output until the apparatus is on the right frequency,when turning on.
To lower the noise threshold further, the low-frequency inputs are fitted with balanced input circuitry.The
input level is precisely adjustable over a broad range,by means of a 0.5dB stepwise variable
attenuators.The transmitter has an auxiliary input,specifically designed for RDS and SCA encoders. A
modulation sample output permits to control other transmitters or STL's with the same internally
processed high-quality mpx signal.
The alphanumeric display permits easy and accurate metering,adjustment and continuous monitoring
of modulation levels,power,operation and internal parameters.All these information may be externally
available on the same RS-232 I/O bus that may be used to remotely control the transmitter.
Above Figure 1-1 shows us the external view of Modulator / Exciter's cabinet, whose control panel has
been simplified to a maximum, being Microcontroller in charge of practically to select and make all
tests and adjustments of all parameters that are relevant to the normal Equipment's performance. Due
to this fact, Front Panel has only a few control elements, since with only the four push buttons
pertaining to Microcontroller (like those used to control movement of cursor in a Computer) and two
keys, these virtually controlling all processes and parameters having place within Equipment.
Microcontroller uses a Liquid-Crystal dot matrix as Alphanumeric Display unit in order to watch
parameter's values, as it's asked for it, as can be seen in the corresponding section in this Manual.
In addition to the serial I/O port, some signals (RF power, ON THE AIR status, Disable line) are available
on a parallel I/O remote socket for easy interfacing with others analog controllers or supervisory
systems. A top-quality stereo encoder may be factory installed as option and even retrofitted in the
field in a second time, requiring minimum technical skill. The powerful internal software and monitoring
functions recognizes its presence and enables its functions.
The RF power amplifier employs a broadband design and has a lot of of reserve: the output power is
feedback-controlled for increased stability still higher than nominal level. High reflected power is limited
to prevent output stage degradation;direct power is accordingly continuously reduced so as not to
exceed the reflected power safety level. A sturdy telecom-grade high efficiency switch-mode power
supply allows operation in a very wide and noisy mains environment.
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 9
1.3 Front panel.
The EM-250 COMPACT DIG Front Panel is very clean and easy to control.The wide alphanumeric
display and the control keyboard allows a simple self-explanatory menu-driven navigation through the
various options. A great care was taken in the design of the software to allow natural feeling with the
controls to allow operation and programming in every respect of the Equipment without needing to
extensively read this manual.
The password management hides some functions and prevents tampering with the most critical
options and data to unauthorized people.
Figure 1-2 shows the simple Equipment's Front Panel, indicating all supervision and control elements:
Fig. 1-2: TRANSMITTER CONTROL PANEL.
These supervision andcontrol elements are numbered in Figure 1-2 as follows:
1 - ON/STBY switch. This ON/STANDBY key do not power off equipment, which is still locked on frequency
and ready to transmit as soon the key is pushed or a remote command is sent.
2 - STANDBY condition indicator LED.
3 - Cooling system's air intake slots.
4 & 7 - Alarm LEDs panel and operation LEDs panel:
ALARM PANEL:
•Alarm red LED lights on in event of any equipment's alarm condition.
•VSWR red LED lights on showing that RF output circuit is overloaded by a severe high VSWR
condition.
•Limiter red LED lights on showing too high audio signal level at equipment's input,and
subsequent operation of baseband peak clipper.
OPERATION PANEL:
•Remote amber LED shows remote-controlled operation is being carried on.
•Lock green LED shows when Channel Oscillator's PLL is properly locked, some tenths of
second after equipment is turned on.
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 10
•On the air green LED works together with STANDBY (2) yellow LED. It lights on when equipment
is in normal operating condition, whereas STANDBY (2) LED is turned off, and vice versa.
5 - Twin-row Alphanumeric dot-matrix LCD display, working directly with Microcontroller unit.
6 - DISPLAY CONTRAST potentiometer, to adjust LCD screen backlighting to a comfortable
contrast level in order to get easy readings.
8 - Programming and parameter selection keyboard:
White keyboard to scroll and navigate through the different menus and options.
OK key (blue). Enter key to confirm some order or command.
CANCEL key (orange). Escape key to cancel menu or command.
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 11
1.4 Rear panel.
All transmitter inputs and outputs are allocated on the rear panel. Figure 1-3 below shows this Panel
indicating all connectors and elements.
Fig. 1-3: REAR VIEW OF TRANSMITTER CABINET.
These elements are numbered as follows:
1 -Mains IEC ON/OFF switch, mains voltage selector,socket and fuses block. Please note that the
transmitter is usually factory pre-set for 220-240VAC nominal Mains voltage.
2 -Main Power Supply's hot air exhaust from internal cooling blower.
3 - RF Power Module's hot air exhaust from cooling fan.
4 -Output RF connector.Type "N"female.
5 - Remote operation DB-9 male connector.
6 - RS-232 serial interface connector. This RS-232 port manages only Tx, Rx and Return data
signals,with no handshake. Being the two former wired signals inverted to the port, it needs a simple
straight wired serial cable with appropriate connectors:usually a female DB-9 or DB-25 female to
the PC port and a male DB9 connector at the transmitter end. Appropriate OMB software is
required for communication. Do not connect the serial cable with neither transmitter or PC turned
on.
7 - RF sample output for frequency measuring or RF signal monitoring, BNC female type connector.
-50dBc.
8 - Right and left channels audio input XLR balanced female connector. For using internal stereo
coder. (See equipment's rear panel for pin connections).
9 - MPX input connector. Type BNC female.For use in pre-coded stereo multiplex signal input. Flat
response from10Hz to 100KHz to feed stereo multiplex signal. Hi - Z unbalanced input (10K:).
10.- AUX connector. Unbalanced Hi-Z BNC female connector,to feed a RDS or SCA encoder output
signal.
11.-LF MONITOR output connector. Baseband modulation output for monitoring, re-broadcasting or
RDS external synchronization. BNC female type, unbalanced Hi-Z (10K:).
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 12
1.5 Inner layout.
Figure 1-4 below shows space occupied and allocation of the different units and PC boards within
equipment, and internal arrangement of cabinet. All boards and units can be easily and quickly
replaced in case of failure:
Fig. 1-4: EM-250 COMPACT DIG TRANSMITTER.UPPER VIEW WITH COVER REMOVED.
Units can be easily identified according with their respective position within cabinet, as numbered in
above Figure 1-4 :
1 - Audio Input board.
2 - Main board.
3 - RF Exciter and Modulation Unit.
4 - Microcontroller Unit.
5 - LCD Display Unit.
6 - RF Power Amplifier Module.
7 - SP-500/48 Main Switching Power Supply.
8 - +15VDC Auxiliary Power Supply.
Space
reserved for
optional
Stereo
encoder
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 13
1.6 Technical specifications.
SIGNAL TO NOISE RATIO Monaural >78dB, typical 86dB (from 30 to 20,000Hz)
Stereophonic >72dB, typical 77dB (from 30 to
20,000Hz)
CCIR WEIGHTED S/N Monaural >75dB, typical 81dB.
Stereophonic >68dB, typical 77dB.
HARMONIC DISTORTION
NOTE:LIMITER SET TO 150KHZ DEVIATION
THRESHOLD.
For ± 75 KHz dev <0.05%, typical 0.02%
For ±150 KHz dev <0.2%, typical 0.05%
STEREO CROSSTALK w/External Encoder <-50dB.
w/Internal Encoder (from 100 to 5000Hz) <-60dB
w/Internal Encoder (from 30 to 15000Hz) <-50dB
PROGRAM AUDIO CHANNEL FREQUENCY
RESPONSE FROM 30 TO 15000HZ
± 0.1dB
ATTENUATION AT AUDIO FILTER REJECTION
BAND (F =19KHZ)
>50dB
DEVIATION LIMITER THRESHOLD Adjustable between 0 and +7dBm
STEREO MULTIPLEX INPUT FREQUENCY
RESPONSE.FROM 10HZ TO 100KHZ
±0.1 dB
AUXILIARY INPUT FREQUENCY RESPONSE
.FROM 10 TO 100KHZ
±0.2 dB
MAINS SUPPLY REQUIREMENTS 90 ~ 260VAC , 50/60 Hz
POWER CONSUMPTION AT 250W RF OUTPUT
LEVEL
600 VA / 480W
OPERATING TEMPERATURES RANGE 0 to +35 ºC recomm.
-10 to +45 º C max
MOUNTING DIMENSIONS (W/O HANDLES) Width:19" Height: 3RU in standard 19" Rack.
DIMENSIONS 483mm width x 125mm height x 334mm depth
MODULATION Frequency, ± 75KHz. peak dev
MODULATION CLASS F3E, F8E
OSCILLATOR'S SYNTHESIS STEPS 10 /100KHz
FREQUENCY ERROR <± 200Hz
FREQUENCY DRIFT <250Hz, over temperature <100Hz/year
RF OUTPUT POWER Adjustable between 2 and 250WRMS nominal
MAXIMUM ALLOWABLE REFLECTED RF POWER 25W
RF HARMONIC PRODUCTS < -70dBc
RF SPURIOUS PRODUCTS <-80dBc.typical -95dBc
RF OUTPUT IMPEDANCE 50: unbalanced. N Female connector
AUDIO /MULTIPLEX INPUT LEVEL Adjustable between -3.5 and +12.5dBm for ±75KHz
peak dev
AUDIO /MULTIPLEX INPUT IMPEDANCE Select.10K: /600:, bal./unbal
COMMON MODE INPUT REJECTION FROM
20 TO 15000HZ
>50dB, typical >60 dB
AUDIO INPUT CONNECTORS XLR Female balanced
SCA/RDS CHANNEL INPUT LEVEL ±7.5KHz dev: adjustable between -12.5 to +3.5dBm.
±2.0KHz dev: adjustable between -24 and -8dBm.
SCA/RDS CHANNEL INPUT IMPEDANCE 10 K: unbal.BNC Female connector
MODULATION OUTPUT LEVEL From 0 to +10dBm at ±75KHz peak dev
PRE-EMPHASIS TIME CONSTANT Variable: 0 /50 /75 µs ± 2%
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 14
CONTE
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2.1 Introduction . . . . . . . . . . . . . . . . . . 15
2.2 Audio processor and R.F. control main board . 19
2.3 Stereo encoder (optional) . . . . . . . . . . . 24
2.4 R.F. Exciter unit . . . . . . . . . . . . . . . . . 27
2.5 R.F. Power Amplifier module . . . . . . . . . . 30
2.6 Control unit and display board . . . . . . . . . 41
2.7 Power supply units . . . . . . . . . . . . . . . .47
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FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 15
2.1 Introduction.
The EM-250 COMPACT DIG transmitter comprises 5 or 6 internal modules, as can be seen in the
general upper view (Figure 1-4) and in the General Wiring Diagram (in next pages). Main units are the
following:
The Main Audio Processor Board.
The Microcontroller Unit and Display Board.
The Stereo Encoder Module (optional).
-The RF Exciter Board.
The RF Power Amplifier Module.
The Switching Regulated Power Supply Units (Main and Auxiliary).
For the detailed description of each module on the following pages, always refer to the corresponding
electrical diagram, included in this section.
Note: the manufacturer reserves the right to change any component value due to production
adjustments.
THIS SECTION IS ONLY AIMED TO GENERAL EXPLANATION,REFERENCE AND SERVICE PURPOSE BY SKILLED
PERSONNEL. AS EXPLAINED IN THE PREVIOUS SECTIONS, INTERNAL ADJUSTMENTS ARE NOT REQUIRED
DURING NORMAL OPERATION. TAMPERING WITH INTERNAL SETTINGS VOIDS THE WARRANTY, MAY HARM THE
APPARATUS AND JEOPARDIZE THE GUARANTEED PERFORMANCE.
DUE TO THE TECHNOLOGY USED,MOST MODULES AND ESPECIALLY THOSE IN SMT ARE NOT INTENDED TO BE
REPAIRED IN CASE OF FAILURE AND MUST BE REPLACED WITH NEW ONES.
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OMB Eng. Dpt.
EM 250 COMPACT DIG
General cabinet layout
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EM 250 COMPACT DIG
Inner layout
OMB Eng. Dpt.
EM 250 COMPACT DIG
General wiring diagram
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FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 19
2.2 Audio processor and R.F. control main board.
This is the most complex board in the transmitter and supports the Audio input processing, its level
adjustment, audio-pass filtering and limiting, the RF control section and the I/O interfaces. It also
interconnects the various transmitter modules with ribbon-type cables. Its electrical diagram is splitted
in two sheets for clarity purpose: they will be examined in sequence. In the first Schematics sheet are
situated the I/O interfaces both audio and digital ports and the analog RF control. Let's start to briefly
consider each block diagram.
In the upper left side of the diagram are located the audio channels amplifier/buffers made with 6 op-
amp sections of IC1 and IC2. Two impedance selector jumpers for the audio channels leads the pack
and a protection network made by resistors and diodes protects the inputs from occasional static
discharges,as required for CE compliance.
Four unity-gain active buffers follow and than two balanced to unbalanced signal converters,which
drive the electronic attenuator in the 2nd sheet. The last op-amp in IC2 (d),amplify the auxiliary channel
input with a -0.1dB upper corner band >>200kHz and drives the third channel of the electronic
attenuator.
Fig. 2-1: MAIN BOARD IS SITUATED IN THE REAR LEFT SECTION OF CABINET.
On the lower left of the diagram are the RS232 interface (IC5)and the parallel remote I/O active
interface with its protection network, built around TR1, TR2 and TR3. A wired OR pull-up makes the logic
levels <1V as 0 and 10-15V for 1.
On the lower right section of the diagram it is located the RF power controller. The RF forward and
reflected power signals coming from the output directional coupler (this located at RF Power Module)
are amplified by IC3 in a symmetrical circuit. The forward-power control circuit,built around IC4a
continuously drives the RF output stage gain,varying the bias supply voltage to the RF output MOSFET
transistor package. The reflected-power limiting circuit IC4b only acts on the same loop when the IC3b
output voltage is greater than the threshold set by the voltage on the R49/R50 network. A third and
fourth section of IC4 filters and buffers the signal coming from the Microcontroller and set the
reference level for the output power loop. TR4 disables the RF output when the synthesizer is not locked
on the correct frequency.
In the upper right section of the sheet it is shown the control bus connector to the Microcontroller Unit,
which carries the digital control lines on the lower pins and the analog lines on the upper ones. From
this connector comes the power supply too: only +12.5V and -12.5V are used in the board.
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 20
Let's now go to the second sheet of this diagram. Beginning from the lower left side,we find IC8, which
makes a 3-channel digitally controlled attenuator. It separately manages left, right and auxiliary
channel, while the externalmultiplex signal is processed in the same channel as the right one. Three
buffer/amplifiers follow each channel: IC7a, IC8a and IC12a. The output of the first two amplifiers drive
the pre-emphasis stages, whose time constants can be digitally set at 0, 50 and 75µs, through the
analog gates of IC9. A limiter stage follows this arrangement, built around D8 and D9 diodes acting as
clippers. By acting on the limiter ’s reference voltage driven by the Microcontroller through IC13a, the
limiter threshold level +Vl and -Vl can be adjusted. RT4, if present, impose a top limit to the limiter.
The signal is then sent to the stereo-encoder circuit ’s input sections if present. At the same time, the
signal on the monaural right channel path is sent to a low-pass filter, consisting of the section built
around IC10 and IC11, which attenuates the frequencies above 15kHz.
The switch IC14 selects the signal issuing from the non-pre-emphasized input section through R124 or
from the pre-emphasis-and-filter section through R128 or from the stereo-encoder through R131.
IC12b buffers the chosen signal and mixes it with that issuing from the auxiliary channel. When
required, the diode D17 further limits the resulting total signal.The latter is then sent to the FM
modulating/exciting circuit via IC12c buffer circuit and adjusted in level by RT6 as required. A separate
section of IC12 separately buffers the modulation signal for monitoring purpose,and sends it to the
modulation output connector.
IC15 deserialize the digital signal sent by the Microcontroller, to control the transmission channels with
IC14 and preemphasis action with IC9. Two output lines from IC15 are used to latch the remote output
lines "FAIL"and "ON THE AIR".
01/11/04 OMB Eng. Dpt.
EM 250 COMPACT DIG
MAINBOARD - I/O & R.F. Control Section
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101/11/04 OMB Eng. Dpt.
EM 250 COMPACT DIG
MAINBOARD - LF Process Section
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01/11/04 OMB Eng. Dpt.
EM 250 COMPACT DIG
Mainboard
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 24
2.3 Stereo encoder (optional).
The encoding circuit uses an 8-step switching technique,which ensures excellent performance with a
relatively simple circuit. In addition, by this technique, the first harmonics that are associated with the
switching devices are the 7th and 9th (266 and 342kHz); this simplifies the design of the low-pass filter on
the multiplex signal.
The signal is filtered beyond 15kHz by the two precision active low-pass filters built around IC1 ~ IC4. It
is then buffered by IC3d and IC4c and applied to the encoding circuit comprised in IC8. Another
higher frequency low-pass filter follows to remove higher order harmonic products. This filter is also
made with highly precise active circuitry built around IC5 and IC6a,b. The latter section (c) of IC6
performs phase equalization.The four analog switches comprised in IC7 permits to select the mono or
the stereo-encoded signal and to slightly vary the encoder gain to adjust for the 90%audio
modulation in stereo vs.100% in mono. Two jumpers on BD1 permit to select either Left or Right or
Left+Right channel for mono operation,with no output level change. As factory configured, both
jumpers are installed, to mix Left and Right channel for "MONO L+R" operation.
Circuits IC10, IC11 make the encoder’s time base; IC9 synthesizes the 19kHz pilot frequency, which is
filtered and buffered by IC5a. A separate 1Vpp output is provided on J2 to drive carrier synchronization
on a possible external RDS generator.
01/11/04 OMB Eng. Dpt.
EM 250 COMPACT DIG
Stereo encoder
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01/11/04 OMB Eng. Dpt.
EM 250 COMPACT DIG
Stereo encoder
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 27
2.4 FM Exciter unit.
This unit includes a classical phase-locked-loop circuit with 10kHz-step synthesis across the entire FM
band. The very low-noise, fundamental-frequency VCO (Voltage-Controlled Oscillator) consists of a
FEToscillator transistor TR5, modulated by the varactor diode set D4~D7, which also sets the operating
frequency. The circuit is sensitivity compensated vs.carrier frequency variation so that its modulation
gain varies less then 0.5dB across the entire operating range. Modulation distortion is typically lower
than 0.03 % with over 90dB S/N ratio in the mono mode in the 30 - 20,000Hz band.
The RF signal is buffered and amplified by three successive transistors TR6 ~ TR8, from which is derived
the feedback signal to the PLL and the drive signal for the output RF stage. This latter is composed by
two small MOSFET transistors TR9 and TR10 and attains some 900mW output level (+29dBm) over the
full FM range.To correctly operate TR9 and TR10 require a gate bias voltage, which is factory pre-set by
RT1.
The digital PLL circuit is entirely contained in IC2, whose frequency reference is derived by a highly
precise temperature compensated oscillator (TCXO1) running at 12.8MHz. To correctly operate on the
chosen frequency, IC2 must be serially programmed with complex data. This task is done by the
Exciter's Microcontroller through 3 control lines.
Fig. 2-2: RELATIVE POSITIONS OF (1) CONTROL CARD AND (2) EXCITER UNIT.
IC1 either performs loop filtering from IC2 frequency comparator output to the varactor diodes and
lock detection. Note that bias voltage is removed from output transistors through TR4 and TR3 to turn
off RF when the PLL is not locked on the right frequency. The control loop was designed to ensure that
crosstalk added to stereo-composite signal is below -55dB at 30Hz, and is virtually not influent at just
slightly higher frequencies.
01/11/04 OMB Eng. Dpt.
EM 250 COMPACT DIG
FM Exciter
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01/11/04 OMB Eng. Dpt.
EM 250 COMPACT DIG
FM Exciter
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 30
2.5 R.F. Power Amplifier module.
This stage is designed with only one high gain BLF-278 MOSFET RF power transistor capsule, in a
broadband class AB1 common emitter design, with +48V DC supply :
Fig. 2-3: 300W FM POWER AMPLIFIER MODULE.
RF Power module includes a driver stage and an output amplifier stage. Figure 2-3 above shows the
general arrangement of this power amplifier module. Numbered elements are as follows:
1 - Cooling fan directed towards heat sink's cooling fins.
2 - Output low pass filter and directional coupler.
3 - RF output Power amplifier section.
4 - RF driver section.
5 - PS-500/48 Main Power supply.
6 - BLF-278 MOSFET output power amplifier twin-transistors capsule.
7 - RF output connector.
8 - RF monitor output.
9 - RF Exciter Unit.
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 31
Detailed views of the three sections composing the Power Amplifier module are shown in Figures 2-4,
2-5 and 2-6 below:
Fig. 2-4: DETAILED VIEW OF INPUT DRIVER STAGE.
Figure 2-4 above shows a magnified view of RF driver stage, a BLF 242 transistor working in class AB
configuration. Numbered elements corresponds to the following description:
1 - Input matching attenuator circuit.
2 - BLF 242 RF Driver transistor.
3 - Bias control circuit.
4 - Input impedance-matching transformer.
5 - Output power amplifier stage PC board.
A resistive input attenuator (1), when present, enhances matching with the preceding unit and
contributes to insulate the two stages. After that, a broadband matching network feeds the transistor
gate.
Output amplifier stage detail can be seen in Figure 2-5.
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 32
Fig. 2-5: DETAIL OF OUTPUT AMPLIFIER SECTION.
Elements numbered in Figure 2-5 can be described as follows:
1 - Input splitter transformer and coupling circuit.
2 - Bias adjustment potentiometer.
3 - Bias regulator circuit.
4 - MOSFET push-pull arranged, twin-transistor capsule.
5 - Output combiner transformer and matching circuit.
Following this amplifier stage, module includes a low-pass filter in order to attenuate or suppress all
harmonics and IM products beyond Band II limits, as shown in Figure 2-6.
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 33
Fig. 2-6: DETAILED VIEW OF LOW-PASS FILTER and DIRECTIONAL COUPLER SECTION.
The three-section low-pass filter (1) attenuates the harmonics to a value that is generally below -70dBc,
following the output transistor drain circuit. Also, included in the RF output path, a directional coupler
(2) generates a dc signal, which is proportional to the forward and reflected RF power, and a RF non-
demodulated sample (RF MONITOR) to be externally used by a frequency counter or a modulation
monitor, for measurements purposes.
The transistor gate is biased by a Zener network and a resistor to set 50mA drain current, with 2.8Vgs.
Varying the control voltage towards a negative supply progressively disables the amplifier transistor,so
effectively acting as an AGC input. In fact the power management circuit, in a closed loop driven by
the output sensor circuitry, varies this voltage.This will accordingly vary the output power to obtain the
pre-set value and cope with alarm and start-up conditions.
The output transistors capsule is a rugged device which easily could pass the nominal 250W power
output, even increasing this power output out of limits, to 300W. OMB suggests never exceeding 250 ~
270W output power, even when the transmitter could generate more than this.
FM Transmitter
Sistemas Electrónicos S.A EM 250 COMPACT DIG
Technical Manual - v1.1 - February 2006 34
Driver FM v1.2.6
DESCRIPTION REFERENCE QUANTITY
100V 100nF C1 1
Electrolytic cap SMD tantalum TAJ 35V 10uF C2 1
SMD 200V RF 150pF C3 1
SMD 200V RF 270pF C4 1
SMD >=50V 68pF C6 1
SMD 1206 100V 1nF C7-C8 2
SMD 1206 10nF C9-C10 2
Zener diode 30V (o 28V) 1N5363B-30V D1 1
Rectifier diode SMD BAS16 D2 1
Zener diode 5V1 SMD BZX84-C5V1 D3 1
Wire 1mm Cu-enamelled Material L1&L2 230mm approx
Inductance 6 turns ext=6mm int=4mm
1mm wire 50nH L1-L2 2
Choke freq=100MHz 800Z B82114RA1 L3-L4 2
Resistor 1R 2W R1-R2 2
Resistor 1/2W 1K8 R3 1
Resistor SMD 15R R4 1
Carbon resistor 1W 220R R5-R6 2
Carbon resistor 1W 10R R7,R14 2
SMD 1206 1/4W 220R R8-R9 2
Resistor SMD 1K R10, R12 2
Potentiometer SMD 1K R11 1
Resistor SMD 820R R13 1
Resistor SMD 51R R15
06/06/02 OMB Eng. Dpt.
EM 250 COMPACT DIG 05.04.01.001
7W FM Driver
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R1 1R 2W
R3
1K8 0.5W
D2
1N5363B-30V o 28V
C1
100nF
C2
10uF
GND GND
GND
28V
Q2
TIP3055
R2 1R 2W
Q1
BLF242
C6
68pF
C3
150pF
C7
1nF
C9
10nF
C8
1nF
C4220pF
C5
18pF
C10
10nF
R4
22R
R8
220
R9
220 R12
51
R13
1K
R10
1K
R14
10R 0.5W
R11
1K
L1
50nH
L2 50nH
L4 VK200
RF IN
RF OUT
L3
VK200
28V
R7
22R 1W
R5
220 1W
R6
220 1W
TL1
33 OHM
TL2
33 OHM
+48V
D4
1N4148
D3
BZX55C5V1
BIAS
R15
680R