This is a basic guide for FM Radio Station Engineers for setting up the RF Transmitter Site. Following these general guidelines and the specific instructions will keep your FM transmitter running for many years
Basic FM Station RF
Design Good Practices
Frank W. Massa - Asia Pacific Sales, Elenos Broadcast
M: +66 83 618-9333 T: +1 831 264-4159
This guide is intended as a reference for basic
recommendations to provide the necessary practices to keep
your equipment operating as intended for normal FM
Transmitter Operation for many years.
A Note on Installation and Warranty Coverage
The customer is responsible for the installation, maintenance
and inspection of the products as well as checking that the
climatic conditions in which the products are placed for their
use are suitable and do not comprise operation
1. Always Follow the Instructions Provided in Transmitter
2. Always follow the Instructions provided by the
manufacturer for Installation of the Antenna, Transmission
Line System, AC line equipment and other station
3. Do not apply Power to the Transmitter until the
Transmission Line, Antenna (or RF Dummy Load) are
WARNING: Do not turn on RF power before
you have connected the device to the
antenna or RF Test Load (Dummy Load)
Follow the Instructions in the Manual
Transmitter Power Warning
Transmitter Test Load
Good Transmitter Site Design
A good transmitter site design will incorporate the following:
1. Good air conditioning. Calculating the AC load for the transmitter waste heat,
other installed equipment, as well as the building solar gain. Waste heat is a
function of AC/RF transmitter efficiency, which is found in the owner’s manual.
2. Good grounding. A good grounding system is a must for all transmitter
sites. This includes lightning and RF grounds. Low impedance paths to a single
point ground is a must.
3. Good power conditioning. Transmitter sites are susceptible to all sorts of utility
company irregularities. Surge protection is a must.
4. Good lighting. Nothing is worst than fumbling around in a half lit transmitter
room trying to make repairs.
5. Adequate work spaces and clearances. Electric panels require 1 meter of
clearance from the front. Cabinet doors should be able to swing fully open. All
access panels should be, well, accessible.
6. Adequate electrical system. Pole transformers and service entrance properly
sized for load. Backup power. Plenty of work outlets around the room.
7. Low VSWR Antenna Transmission System. Make sure the Antenna,
Transmission line and connectors are all designed to reduce the VSWR
Climatic Control of the Transmitter Equipment
Operate within the Equipment Specifications:
1. Good HVAC System. Provide a good System that keeps the Equipment at
approximately 25 degrees C for Optimal Operation and within the Equipment
Specifications of -5 to +45 C, and has good airflow with a proper air filtration to
prevent dust in the room
2. Humidity Control. An Environment within the specification of 95% @ 40 C
Tx Temp Display
HP Tx with
for use with
Dealing with Humidity
Many electronic devices have humidity specifications, for example, 5 to 95%. At
the top end of the range, moisture may increase the conductivity of permeable
insulators leading to malfunction. A particular danger to electronic
items, regardless of the stated operating humidity range, is condensation.
When an electronic item is operated in a cool place (Transmitter Site with Aircon)
and then becomes a warm and humid environment, condensation may coat circuit
boards and other insulators, leading to short circuit inside the equipment. Such
short circuits may cause substantial permanent damage if the equipment is
powered on before the condensation has evaporated.
Turning off the Transmitter and Air Conditioning in the evening and starting again
in the morning causes condensation which over time can cause corosion and/or
moisture build-up leading to degraded performance and possible malfunction
Tip: In Tropical Areas Use a Dehumidifier to keep the Humidity within
In Humid Climates, or when turning the Transmitter off for extended periods to
reduce condensation dehumidifiers are available a most consumer appliance
stores. It’s a great investment.
A ground system provides four primary
1. To help disperse or divert energy from lightning
2. To provide safety in case some problem or
fault energizes the cabinet or equipment
chassis with dangerous voltages
3. To provide a controlled RF return path for
antennas and transmission line
4. To provide a highly-conductive path for induced
or directly-coupled radio-frequency
currents, rather than having them flow in lossy
(Refer to Each Manual)
Transmitter site Grounding System
Tower Grounding: Refer to the Recommendations of the tower manufacturer
Antenna Grounding: Refer to the Recommendations of the antenna manufacturer
RF Cable Grounding
Cable Grounding: Refer to the Recommendations of the cable manufacturer
AC Line Protection
Total Equipment Protection:
1. Automatic Voltage Regulators
2. AC Surge Protection
3. Lightning Surge Protection
4. Isolation Transformers
5. Uninterruptable Power Supply
6. Ground System
Automatic Voltage Regulator (AVR)
The automatic voltage regulator or AVR, as the name
implies, is a device intended to regulate voltage
automatically: that is to take a varying voltage level and turn
it into a constant voltage level. Keep the AC Voltage within
your Equipment Limits!
AC Surge Protection
In power lines, usually large amounts of voltage are induced (typically very short
time with high amplitude) due to lightning (direct or indirect strikes) or Transients
(Transients caused by other equipment are usually caused by the discharge of
stored energy in inductive and capacitive components.
Electric motors, such as those used in diesel generators, elevators, heating, air
conditioning, refrigeration or other inductive loads, can create a continuous
stream of 250V to 1000V transients. DC motor drives, variable speed AC motor
drives, DC power supply switching, and portable power tools are other sources of
A surge protector (or surge suppressor) is an appliance designed to protect
electrical devices from voltage spikes. A surge protector attempts to limit the
voltage supplied to an electric device by either blocking or by shorting to ground
any unwanted voltages above a safe threshold.
You don’t need a “Direct Hit” to Damage Your Equipment
Used to electrically isolate sensitive electrical equipment from
the fluctuations in the supplied power. Most transformers can
act as isolation transformers. Note there is no physical
connection between the primary and secondary.
Uniterrupable Power Supply
An uninterruptible power supply, also uninterruptible
power source, UPS or battery/flywheel backup, is an
electrical apparatus that provides emergency power to a load
when the input power source, typically mains power, fails.
VSWR is used as an efficiency measure for transmission
lines, electrical cables that conduct radio frequency signals,
used for purposes such as connecting radio transmitters and
receivers with antennas. Impedance mismatches in the cable
and antenna reflect the power back to the transmitter,
preventing all the power from reaching the destination end.
An ideal transmission system would have a VSWR of 1:1,
with no reflected power.
An infinite VSWR represents complete reflection, with all the
power reflected back to the transmitter.
Voltage standing wave ratio (VSWR) can wreak havoc in a
transmitter when it suddenly increases. FM transmitters are
susceptible to VSWR problems due to antenna problems or
transmission line damage.
- Always check the transmission line and Antenna System
after a major storm
- Always take action to reduce power when the VSWR is
TX VSWR and IPF
IPF (Intelligent Proportional Foldback):
IPF is an intelligent system that allows the transmitter to stay
“ON AIR” into mismatched loads.
2:1 at full power. Automatic power reduction beyond 1.7:1.
Transmitter is protected from open and short circuit.
Recommended Document: ETSI – ETR 132
Stay On Air!
Frank W. Massa
Asia Pacific Sales
Elenos / 305 Broadcast
M: +66 83 618-9333
T: +1 831 264-4159