Basic FM Radio Station RF Design Good Practices


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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

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Basic FM Radio Station RF Design Good Practices

  1. 1. Basic FM Station RF Design Good Practices Prepared By: Frank W. Massa - Asia Pacific Sales, Elenos Broadcast M: +66 83 618-9333 T: +1 831 264-4159
  2. 2. 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.
  3. 3. 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 User Manual 2. Always follow the Instructions provided by the manufacturer for Installation of the Antenna, Transmission Line System, AC line equipment and other station accessories. 3. Do not apply Power to the Transmitter until the Transmission Line, Antenna (or RF Dummy Load) are connected
  4. 4. 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 Note: Coax Switch or Manual U-Link Suggested Transmitter Power Warning Transmitter Test Load
  5. 5. 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
  6. 6. 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 Screen Install and Maintain your Air Conditioning and Heating where needed HP Tx with Air Extractor for use with a ducting system
  7. 7. 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 specifications
  8. 8. Controlling Humidity 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.
  9. 9. Grounding Systems A ground system provides four primary functions: 1. To help disperse or divert energy from lightning strikes 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 soil
  10. 10. Equipment Grounding Transmitter Ground (Refer to Each Manual) Transmitter site Grounding System
  11. 11. Tower Grounding Tower Grounding: Refer to the Recommendations of the tower manufacturer
  12. 12. Antenna Grounding Antenna Grounding: Refer to the Recommendations of the antenna manufacturer
  13. 13. RF Cable Grounding Cable Grounding: Refer to the Recommendations of the cable manufacturer
  14. 14. 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
  15. 15. 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!
  16. 16. 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 transients.) 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.
  17. 17. Lightning Protection You don’t need a “Direct Hit” to Damage Your Equipment
  18. 18. Isolation Transformer 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.
  19. 19. 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.
  20. 20. Low VSWR 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.
  21. 21. MAX VSWR 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 high
  22. 22. 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.
  23. 23. Recommended Document: ETSI – ETR 132
  24. 24. Stay On Air! Prepared by: Frank W. Massa Asia Pacific Sales Elenos / 305 Broadcast M: +66 83 618-9333 T: +1 831 264-4159 Skype: fstarport Twitter: @fstarport