Radio Frequency (RF)

Radio FrequencyAn antenna transmits and receives radio-frequency signals, allowing a two-way radio to communicate. Antenna type, frequency, height and location can all affect radio performance and coverage. (RF) refers to electromagnetic waves used to transmit information wirelessly. Two-way radios use radio frequencies to send and receive voice and data communications between radios, repeaters and other radio-system infrastructureRadio infrastructure is the equipment and supporting systems behind a professional two-way radio network, including repeaters, antennas, base stations, network connections, power systems and dispatch equipment..

The frequencyFrequency is the number of cycles a radio wave completes each second, measured in Hertz. In two-way radio, frequency determines where a transmission operates within the radio spectrum. selected for a radio systemA Radio System is a complete communication solution comprising two-way radios and, where required, equipment such as repeaters, antennas, base stations, mobile radios and network infrastructure. affects how signals propagate and can influence coverageRadio Coverage is the geographical area in which a two-way radio system can provide reliable communication. Coverage depends on the radios, antennas, frequency, terrain, buildings and system infrastructure., antennaAn antenna transmits and receives radio-frequency signals, allowing a two-way radio to communicate. Antenna type, frequency, height and location can all affect radio performance and coverage. requirements and the way radio signals behave around buildingsAn antenna transmits and receives radio-frequency signals, allowing a two-way radio to communicate. Antenna type, frequency, height and location can all affect radio performance and coverage. and terrain.

What is Radio Frequency?

Radio frequency is the part of the electromagnetic spectrumSpectrum is the range of radio frequencies used for wireless communication. Two-way radios operate within specific parts of the radio spectrum, subject to frequency allocation and licensing requirements. used for radio communication.

Frequency is measured in Hertz (Hz), with professional radio systems commonly operating in the MHz (megahertz) range.

For example:

150 MHz = 150 million cycles per second

A two-way radio converts voice or data into a radio signal, transmits it at the configured frequency and another compatible radio receives and decodes the signal.

How radio frequency works

A simplified two-way radio transmissionTransmission is the process of sending voice, data or signalling from a radio using a radio-frequency signal to another radio, repeater or communication system. is:

Voice → Radio → RF Signal → Antenna → Air → Receiving Antenna → Radio → Voice

The transmitting radio converts information into a modulated RF signal.

The receiving radio detects the signal and converts it back into usable audio or data.

Radio frequency and two-way radios

Every radio system operates within an allocated frequency range.

A radio must be configured to operate on frequencies compatible with the rest of the system.

For example:

Radio A → RF Frequency → Radio B

If the radios are not configured correctly, they may not be able to communicate.

Radio frequency and channels

A radio ChannelA two-way radio channel is a programmed set of communication settings, typically including frequency and signalling, that allows compatible radios to communicate with one another. normally represents a programmed set of communication parameters, which can include transmit and receive frequencies.

For a simple radio system:

Channel 1 → Frequency A

Channel 2 → Frequency B

The user normally selects the channel rather than manually entering a frequency.

Radio frequency and transmit frequency

The Transmit Frequency is the frequency used by a radio when it sends a signal.

The transmitting radio’s signal must be received on the appropriate frequency by the other equipment.

Radio frequency and receive frequency

The Receive Frequency is the frequency on which a radio listens for incoming communication.

In a simple radio-to-radio system, the transmit and receive frequencies may be the same.

In a repeaterA Repeater receives a two-way radio transmission and retransmits it, usually from an elevated location, to extend the coverage and reliability of a radio communication system. system, they are normally different.

Radio frequency and repeater systems

A Repeater receives a transmission on one frequency and retransmits it on another.

For example:

Radio → Repeater Receive Frequency

Repeater → Radio Transmit Frequency

This arrangement allows radios to communicate over greater distances than may be possible with direct radio-to-radio communication.

Radio frequency and duplexers

Repeater installations can use a Duplexer to allow the transmitter and receiverA Receiver is the part of a two-way radio that detects and processes incoming radio signals, converting them into audible voice or usable data for the user. to operate through a shared antenna while using different frequencies.

The separation between the transmit and receive frequencies is important to the design of the repeater system.

Radio frequency and frequency separation

The difference between a repeater’s transmit and receive frequencies is known as frequency separation or offset.

The required separation depends on the frequency band and radio system.

This is one of the parameters that must be correctly programmed into compatible radios.

Radio frequency and spectrum

The radio-frequency spectrum is a finite resource.

Different services use different parts of the spectrum, including:

• Broadcasting
• Mobile communications
• Aviation
• Maritime communications
• Satellite services
• Professional radio
• Public-safety communications

Regulators coordinate frequency use to reduce interferenceRadio interference occurs when unwanted radio-frequency signals or electrical noise disrupt two-way radio communications, causing distorted audio, broken transmissions, reduced coverage or loss of communication. and ensure efficient use of spectrum.

Radio frequency and Ofcom

In the UK, OfcomOfcom (Office of Communications) is the UK's communications regulator. For two-way radio users, Ofcom manages and regulates access to radio spectrum and the use of radio frequencies in the UK. manages and regulates the use of radio spectrum.

Professional radio users may require an appropriate licence depending on the service and frequencies being used.

A licensed radioA Licensed Radio is a two-way radio operated under an appropriate radio licence. Licensed systems can provide greater control over frequencies, coverage and infrastructure than licence-free radio services such as PMR446. system must operate within the conditions of its authorisation.

Radio frequency and Ofcom Business Radio Licence

A professional business-radio system in the UK may operate under an Ofcom Business Radio LicenceAn Ofcom Business Radio Licence authorises businesses and organisations in the UK to use specified radio frequencies for professional two-way radio communication, subject to the licence conditions..

The licence specifies the authorised frequencies and other operating conditions.

Having a radio capable of transmitting on a particular frequency does not automatically give the user permission to use that frequency.

Radio frequency and licence-free radio

Some radio services operate without an individual business-radio licence, subject to defined technical restrictions.

PMR446 is a well-known example.

PMR446 equipment must operate within the applicable technical requirements for the licence-free service.

Radio frequency and PMR

Professional Mobile Radio (PMR)Professional Mobile Radio (PMR) describes private two-way radio systems designed for business and professional users, ranging from simple radio networks to advanced digital and multi-site systems. systems can operate across different frequency bands depending on the service, equipment and licensing arrangements.

Frequency selection is an important part of professional radio system design.

Radio frequency and DMR

Digital Mobile Radio (DMR)Digital Mobile Radio (DMR) is an ETSI digital radio standard for professional two-way communications, supporting voice, group calling, data and other features on compatible radio systems. systems can operate on different frequency bands depending on the equipment and regulatory environment.

DMR defines a digital radio standard, but the standard itself does not mean that every DMR radio operates on the same frequency.

The operating frequency is determined by the radio system and its configuration.

Radio frequency and analogue radio

Analogue two-way radios also use RF signals.

Voice information is modulated onto the radio-frequency carrier and transmitted through the antenna.

Radio frequency and digital radio

Digital radios encode voice or data into digital information before transmitting it using an RF signal.

The underlying transmission still relies on radio frequency.

Digital technology changes how information is encoded and processed rather than eliminating the need for RF transmission.

Radio frequency and modulation

Modulation is the process used to place information onto a radio-frequency carrier.

Different radio systems use different modulation methods.

The modulation method must be compatible between transmitting and receiving equipment.

Radio frequency and bandwidth

Bandwidth describes the range of frequencies occupied by a radio signal.

A radio channel therefore occupies a portion of the available RF spectrum.

Efficient spectrum use is particularly important where many radio users operate within the same geographical area.

Radio frequency and narrowband

NarrowbandNarrowband describes a radio communication system that uses a relatively small amount of frequency spectrum to transmit information. It is widely used in professional two-way radio to make efficient use of available radio channels. radio systems use relatively small amounts of RF spectrum for each communication channel.

Modern professional radio systems commonly use narrowband channel arrangements to make efficient use of available spectrum.

Radio frequency and interference

Interference occurs when unwanted RF energy affects a communication.

Potential sources include:

• Other radio transmitters
• Electrical equipment
• Poorly designed installations
• Adjacent-channel signals
• Industrial equipment
• Atmospheric or environmental sources

Interference can reduce communication quality or prevent a radio from receiving a usable signal.

Radio frequency and adjacent-channel interference

Adjacent-channel interference occurs when energy from a nearby frequency affects another communication channel.

Good frequency planning and appropriate equipment filtering help reduce this problem.

Radio frequency and co-channel interference

Co-channel interference occurs when two systems use the same frequency and their signals overlap in an area where they can affect one another.

Frequency coordination is therefore important when planning professional radio systems.

Radio frequency and signal strength

The strength of a received RF signal affects communication quality.

Signal strength can be influenced by:

• Transmitter powerAn antenna transmits and receives radio-frequency signals, allowing a two-way radio to communicate. Antenna type, frequency, height and location can all affect radio performance and coverage.
• Distance
• Antenna
• Terrain
• Buildings
• Frequency
• Atmospheric conditions

A stronger signal is not automatically a better system if interference or other problems are present.

Radio frequency and propagation

Propagation describes how RF signals travel through the environment.

Radio signals can:

• Travel directly between antennas
• Reflect from surfaces
• Diffract around obstacles
• Be absorbed by materials
• Be scattered by terrain and structures

Different frequencies can behave differently in particular environments.

Radio frequency and buildings

Buildings can significantly affect RF propagation.

Materials such as:

• Concrete
• Steel
• Glass
• Brick
• Metal cladding

can weaken or alter radio signals.

This is why a radio system that works well outdoors may require additional infrastructure to provide reliable indoor coverage.

Radio frequency and terrain

Hills, valleys and other terrain features can obstruct radio signals.

A repeater installed at a suitable elevated location can help overcome some terrain-related coverage limitations.

Radio frequency and line of sight

Some radio frequencies and system designs rely heavily on a clear Line of Sight (LOS) between transmitting and receiving antennas.

Obstructions can reduce signal strength and coverage.

The importance of line of sight varies according to frequency, antenna height and environment.

Radio frequency and coverage

RF frequency is one of several factors affecting radio coverage.

Coverage is also influenced by:

• Antenna height
• Antenna type
• Transmitter power
• Receiver sensitivity
• Terrain
• Buildings
• Interference
• Repeater location

A frequency change alone does not necessarily solve a coverage problem.

Radio frequency and dead spots

A Dead SpotA Dead Spot is an area where two-way radio communication is weak, unreliable or unavailable. Dead spots can be caused by buildings, terrain, distance, interference or inadequate radio coverage. is an area where communication is unavailable or unreliable.

Dead spots can result from:

• Terrain
• Buildings
• Signal attenuation
• Interference
• Poor antenna positioning
• Insufficient system infrastructure

A Site SurveyA Site Survey is an assessment of a location to determine whether a two-way radio system will provide the required coverage, reliability and performance. can help identify RF coverage problems.

Radio frequency and antennas

An Antenna converts electrical signals into electromagnetic RF energy when transmitting and performs the reverse function when receiving.

The antenna must be suitable for the operating frequency.

An antenna designed for one frequency range may perform poorly outside its intended range.

Radio frequency and antenna height

Increasing antenna height can improve coverage by providing a clearer propagation path.

This is particularly important for repeater and base-station installations.

Radio frequency and power output

Power OutputPower Output is the amount of radio-frequency energy produced by a two-way radio's transmitter, normally measured in watts. It is one factor affecting coverage, alongside frequency, antenna, terrain and other conditions. determines how much RF energy a transmitter produces.

Higher power can improve the received signal in some situations, but it does not automatically produce proportionally greater coverage.

Power must remain within applicable regulatory and equipment limits.

Radio frequency and receiver sensitivity

Receiver sensitivity describes how effectively a radio can detect weak signals.

A sensitive receiver can potentially receive weaker signals, although overall system performance also depends on interference, antenna performance and other factors.

Radio frequency and selectivity

Receiver Selectivity describes the ability of a radio to receive the desired signal while rejecting unwanted signals on nearby frequencies.

Good selectivity is particularly important in areas where many radio systems operate.

Radio frequency and encryption

EncryptionEncryption protects two-way radio communications by converting voice or data into a secure form that can only be understood by authorised radios with the correct encryption capability and keys. protects the information being communicated.

It does not change the basic fact that the communication is transmitted using RF.

Encryption and RF transmission therefore address different aspects of radio communication.

Radio frequency and GPS

A radio with GPS (Global Positioning System)GPS is a satellite-based positioning system that allows compatible two-way radios to determine their location. GPS data can support tracking, dispatch, fleet management and Geo-Fencing. capability may contain a separate receiver that obtains positioning information from satellite signals.

The GPS function and the radio’s primary communication frequency are separate systems, although both involve radio-frequency signals.

Radio frequency and Bluetooth

Bluetooth also operates using RF, but it uses different frequencies and communication methods from professional two-way radio systems.

A radio may contain Bluetooth connectivity alongside its main radio transceiverA Transceiver combines a transmitter and receiver in one device, allowing a two-way radio to both send and receive radio signals..

Radio frequency and Wi-Fi

Wi-FiWi-Fi is a wireless networking technology that connects compatible devices to a local or wider network. In radio systems, it can support programming, updates, data services and IP-based communications. uses RF signals to transmit data wirelessly.

Professional communication systems can use Wi-Fi as part of their networkA Network is a connected system of radios, equipment and infrastructure that allows users to communicate across a defined area. Radio networks can range from simple radio-to-radio systems to large multi-site networks. infrastructure, particularly for IP-based services.

Wi-Fi and two-way radio may therefore coexist within the same overall communication environment.

Radio frequency and cellular networks

Mobile networks such as 4G and 5G also use radio frequencies.

Push-to-Talk over Cellular (PoC)Push-to-Talk over Cellular (PoC) provides radio-style push-to-talk communication over cellular or IP networks, allowing users to communicate across wide areas where suitable network connectivity is available. uses cellular or IP connectivity rather than relying solely on a dedicated professional-radio frequency.

This means PoC and conventional two-way radio use different network architectures even though both ultimately rely on wireless technologies.

Radio frequency and RF exposure

Radio transmitters produce RF electromagnetic fields.

Equipment must be designed and operated in accordance with applicable safety and regulatory requirements.

Exposure depends on factors including:

• Transmitter power
• Antenna characteristics
• Distance
• Operating time
• Installation

Professional installations should follow the manufacturer’s and relevant regulatory guidance.

Radio frequency and mobile radios

Vehicle-mounted Mobile Radios use RF signals to communicate with other radios or radio infrastructure.

The vehicle antenna is an important part of the RF system.

A correctly installed external antenna can provide significant advantages compared with a poorly positioned antenna.

Radio frequency and portable radios

Portable Radios use an integrated or connected antenna.

Because the antenna is close to the user’s body and often operates at a lower height than a vehicle or building-mounted antenna, portable-radio coverage can differ from that of a mobile radioA Mobile Radio is a two-way radio designed to be installed in a vehicle. It normally uses the vehicle's power supply and an external antenna to provide reliable communication while travelling or working in the field..

Radio frequency and base stations

A Base StationA base station is a fixed two-way radio installed at a permanent location, allowing an operator to communicate with handheld or mobile radios across a site or operating area. is normally installed at a fixed location and can use a more substantial antenna system than a handheld radio.

A suitable antenna location can significantly improve the performance of a base station.

Radio frequency and radio hire

Professional Radio HireRadio Hire is the temporary rental of two-way radios and related communication equipment for events, projects and operational requirements, providing professional communication without purchasing the equipment. systems require suitable frequencies and configurations for the intended application.

Depending on the service, hired radios may operate on licensed business-radio frequencies or appropriate licence-free services.

The radios must be configured to comply with the applicable operating conditions.

Radio frequency and events

Large events can require carefully planned RF arrangements because many communication systems may operate in the same area.

Frequency coordination can help reduce interference between:

• Radio users
• Production teams
• Security
• Event management
• Contractors
• Other wireless systems

Radio frequency and construction

Construction sites can contain large amounts of metal, machinery and temporary structures that can affect RF propagation.

A professional radio system should therefore be assessed for the actual site environment.

Radio frequency and security

Security teams often depend on reliable radio coverage across buildings and outdoor areas.

RF planning can help identify where repeaters, antennas or additional infrastructure may be required.

Radio frequency and transport

Transport operations may use radios across vehicles, depots and control centres.

The RF system must be designed around the geographical area, vehicle environment and required coverage.

Radio frequency and agriculture

Agricultural sites can cover large areas and may include buildings, machinery, trees and uneven terrain.

RF coverage can therefore vary significantly across a farm.

A repeater or elevated antenna may be appropriate where direct radio communication is insufficient.

Radio frequency and radio system design

Professional RF planning considers:

1. Required coverage.
2. Operating environment.
3. Frequency availability.
4. Licensing.
5. Number of users.
6. Interference.
7. Antenna locations.
8. Transmitter power.
9. Repeater requirements.
10. Future expansion.

Radio frequency and site surveys

A Site Survey can be used to assess actual RF coverage at a location.

A survey may identify:

• Strong-signal areas
• Weak-signal areas
• Dead spots
• Interference
• Suitable repeater locations
• Antenna positioning requirements

This can help engineers design a system based on the real environment rather than assumptions about coverage.

Radio frequency limitations

Radio frequency alone does not determine whether a communication system will work.

Other important factors include:

• Equipment quality
• Antenna performance
• Receiver sensitivity
• Transmitter power
• System design
• Interference
• Network infrastructure
• Licensing
• User environment

Radio frequency and DCS

DCS designs and supplies professional two-way radio systems using frequencies appropriate to the application and licensing requirements.

We can assess coverage, equipment, antennas and repeater requirements to help provide reliable radio communication across sites, buildings, vehicles and wider operational areas.