Radio 101: Two-Way Communication Explained

Radio 101: Terminology and Formats Explained

What is a Two-Way Radio?

A two-way radio is simply a radio that can both transmit and receive (a transceiver). In broader terms, most of voice wireless communications systems, including cellular systems, fall into two-way radio definition.

A Two-way radio refers to a radio system mainly used for group call communication and is also known as:

  • Professional Mobile Radio (PMR)
  • Land Mobile Radio (LMR)
  • Private Mobile Radio (PMR)​
  • Public Access Mobile Radio (PAMR​)

Portable two-way radios are often called walkie-talkies or handie-talkies. Two-way radios are also available in mobile (installed in a vehicle) and base (in your office) configurations as well as utilizing radio network infrastructure.

A two-way radio is typically equipped with a “Push-To-Talk” PTT button to activate the transmitter. User just simply presses the PTT button and can immediately start to talk. User releases the PTT button to listen to others.

Two-way radio can “talk” directly to other radios or use radio network infrastructure. A direct talk among radios (usually also known as direct operation or talk around mode) has limited range due to limitation of radio power. To overcome this limitation, a radio repeater can be utilized to extend communication range.

Why Use a Two-Way Radio?

With various wireless technology options and two way radio being one of the “earliest” wireless technologies, you might be questioning whether two-way radio is still a current technology. The answer is yes and the following are the key points that uniquely differentiate two-way radio to other wireless technology:

Instant communication

Two-way radio provides instant communication. The user only needs to press the “Push-To-Talk” (PTT) button and within fraction of a second, this user can immediately talk to convey his/her messages.

This is due to a quick call setup time embedded in the technology. This instantaneous communication capability is one of key factors of why many organizations rely on two-way radio for their tactical or operational communications.

Group communication

Another distinct feature of two-way radio is its capability to facilitate “one-to-many” group communication (also known as “group call”) very efficiently. By efficient means that one user can talk to one, five, tens, hundreds, thousands of users at the same time. The user doesn’t need to repeat the same message over and over again if he/she needs to convey to more than one user.

In addition, two-way radio performs the group communication using minimum RF channel resources. If all of users reside in the same area, most of the time, you only need one channel resource to talk to these hundreds of users.

Why Not Other Wireless Systems?

Every wireless technology has their advantages and disadvantages. The choice of which technology is the most suitable for one’s organization depends on whether that particular technology can meet the user requirement.

For those users who need to:

  • Work in a group​
  • Communicate instantly
  • Mobile

Two-way radio can be considered as appropriate solution compared to other wireless technology. Following are the reason why other wireless technology, such as public cellular network, may not be able to meet the above requirement:

Communicate Instantly

Imagine you are in the field and face an emergency situation and need to communicate immediately to declare your situation. If you are using a cellular phone, for example, you need to dial a number, wait for a while when the call is being set-up and connected, ring at the other side and finally answered. This process can take a few second and during that valuable time, your emergency situation can become worsen.

PTT Button

With two-way radio, you just press the PTT button and shout out “emergency” to get attention and immediate help. Of course, this is assuming that RF channel are available. We will discuss later on two-way radio features that can overcome RF channel congestion and give highest priority for emergency users, a feature that are not available in other wireless technology.

Group communication

Say you need to inform your 5 staff that a meeting has been rescheduled. If you call them one-by-one, it will take some time. With a two-way, you just select your talkgroup and press the PTT button and start to talk to your 5 staff at the same time. Now, just imagine if you need to broadcast your message to 1000 staff in the field.

While some wireless system allows a group calling, it typically limits the number of group member that you can talk at one time. With a radio, you just need to “talk once and heard by many”.

Who Are ​Two-Way Radio Users?

Two-way radios have been used for many years by various organizations and industries. Due to the nature of their operational needs, they have to utilize radios to address their communication needs. Examples of organizations and industries that rely on two-way are:

  • Public Safety organization: Police, Fire, Emergency Medical Services / Ambulance, Disaster Recovery agency​
  • Security: Military, Intelligence agencies
  • Transportation: Railway, Airport, Seaport, Light Rail, Subway
  • Oil & Gas companies
  • Utility companies: Electricity, Gas, Water, Telephone, Cable TV
  • Transport Service companies: Taxi, Limos, Trucking
  • Construction companies: Commercial, Residential, Road and Bridge
  • Hospitality industries: Hotel, Resort, Restaurant, Tourism
  • Government agencies: Ministries, Local government, Municipal, Embassies, Public Works
  • Services industry: Delivery companies, Towing companies
  • Manufacturing
  • Contractors: Electrical, Excavating, Plumbing, Roofing
  • And many others…

In other words, users of two-way radio are any agencies or businesses with multiple staff or workers who work in group and mobile.

Are you compliant with the VHF/UHF narrow banding mandate?

On January 1, 2013, all public safety and business industrial land mobile radio systems operating in the 150-512 MHz radio bands are mandated by the FCC to cease operating using 25 kHz technology, and begin operating using at least 12.5 kHz efficiency technology.

This deadline was the result of an FCC effort that began almost two decades ago to ensure more efficient use of the spectrum and greater spectrum access for public safety and non-public safety users. Licensees that are not operating at 12.5 KHz efficiency are in violation of the Commission’s rules and could run the risk of incurring serious fines and dysfunctional equipment.

Two- Way Radio Terms/Definitions:


(Conventional) Analog systems may communicate a single condition. Information is sent by changing the frequency, amplitude or phase of the radio signal.


Digital systems may communicate text from computer-aided dispatch (CAD). Information is converted to true data bits and applied directly to the radio transmitter using FDMA or TDMA or voice.


​As DMR is a fully public, open standard backed by a huge variety of suppliers. Through this users have both the security of supply and the advantages of continuous, competitive development. Open standards encourage wide ranging supplier participation; there are many examples of the successes of technologies developed in this way. The DMR standard scores highly against legacy analogue systems and other digital approaches.

DMR Logo


A frequency on which a two-way can communicate; determined by the capability of the make/model radio


(What a channel operates on) The number of occurrences of a repeating event per unit time. Also known as band.


(High-frequency) the range of frequencies in the radio spectrum between 3 and 30 megahertz.


(Ultra-high frequency) designates the ITU radio frequency range of electromagnetic waves between 300 MHz and 3 GHz (3,000 MHz), also known as the decimeter band or decimeter wave as the wavelengths range from one to ten decimeters; that is 10 centimeters to 1 meter. 800 MHz is also considered.


(Very high frequency) is the ITU-designated range of radio frequency electromagnetic waves from 30 MHz to 300 MHz


(Frequency Division Multiple Access) gives users an individual channel allocation


(Time Division Multiple Access) shares single frequency with multiple users


​NXDN is an open standard Common Air Interface (CAI) technical protocol for mobile communications. It was developed jointly by Icom Incorporated and Kenwood Corporation.

Nexedge Logo

Intrinsically Safe (IS):

(Also known as FM Approved) Intrinsic safety (IS) is a technology for safe operation of electronic equipment in locations where explosive gases may be present. Intrinsically safe radios are designed so the electrical energy in the radio is low enough that ignition of the explosive gases will not occur.

Manufacturers must meet specific standards in order for a product to be certified as ‘Intrinsically Safe’. Radios meeting this standard have the designation ‘Intrinsically Safe’ or ‘FM Approved’ on their documentation.

Land Mobile Radio (LMR):

Traditionally private systems that allow communication between a base and several mobile radios and can share a single frequency or use multiple frequencies.


Wireless communications systems and devices which are based on radio frequencies, and where the path of communications is movable on either end; typically mounted in a vehicle.


Might be referred to as a walkie-talkie or hand-held radio.

Two Way Radios not Walkie Talkies

Push-to-Talk (PTT):

All two-ways have a PTT button. If you want to transmit you push the button which opens the channel for transmission. Otherwise, no transmission occurs. Some microphone models offer both VOX (Voice Operated Switch) and PTT options.


A radio repeater is a combination of a radio receiver and a radio transmitter that receives a weak or low-level signal and retransmits it at a higher level or higher power, so that the signal can cover longer distances without degradation. Also known as a base station, site, or site repeater.

Relay Delay:

When using a repeater, keeps the repeater transmitter open a short time after a radio user releases the PTT switch. This allows a user group to conduct a normal conversation without delays from re-activating the repeater. This “polite pause” can be set from 0-7 seconds.


The number of miles of range advertised by two way manufactures is always the maximum range that the radio will get under perfect circumstances. Many things can affect the range, such as trees, bushes, buildings, vehicles, or almost anything that could interfere with line of sight. Weather and solar events can also affect range.


(Receive) reproduction of audio signals from the transmission of another radio


(Transmit) To send or convey from one person or place to another.


Most radios today have a scanning feature. All business grade radios have a scanning feature; scanning does what the name implies, it scans for traffic on the channels you designate. Once it detects a transmission it stops so that you can hear the transmission.

You can select multiple channels you wish to ‘scan’ for communications, the radio will only pick up communications on those channels you selected. This can be a handy feature if you have multiple groups assigned to each channel, you can use a separate ‘broadcast’ channel to relay messages to everyone.

Each group can set their radio to scan both their group’s channel and the ‘broadcast’ channel. Or, maybe you have two groups who need to hear each other’s communications at times. When they need to hear each other, all they do is set their radio to scan both channels. Most business grade radios have several different types of scanning functions:

  • Normal scan: sequentially scans all the selected channels, by channel number.​
  • Priority Scan: scans all the selected channels while constantly monitoring the primary channel
  • Talk Back: enables the user to transmit on the channel that the scan stopped on last
  • Start / Stop / Pause Scan: allows user to start, stop, & pause the scan function
  • Dual Watch: Allows user to choose 2 priority channels to scan
  • Nuisance Channel Delete: Temporarily delete a channel from scanning list.
  • Power-on scan: Automatically starts the scan function when the radio is turned on.
  • Priority Rewrite: Allows users to re-assign the priority channel from what was programmed in the radio
  • Talk Around: When radios are in proximity and signal strength is good, this function by-passes the repeater.
  • Mode Dependent Scan: Set different scan modes by channel
  • Scan List: Have different scan lists, changing scan list as needed.
  • Voting scan mode: selects the strongest signal as the radio scans for a repeater station.
  • Scan Set: This function allows you to easily set and / or change the channel or group your radio is scanning.
  • Group Scan: This scanning feature is used to monitor multiple channels or groups of channels once the channels are programmed into the transceiver.
  • Follow-Me Scan: Allows the user to designate a channel to scan in addition to the scan settings already programmed in the radio. As an example, if Channels 1, 3, and 5 are programmed for ‘scanning’, the user may additionally assign Channel 2 as their “User-assigned” Priority Channel via the “Follow-Me” feature. The User-assigned Priority Channel will automatically be checked every few seconds along with the other programmed channels.
  • Edit Scan List: Add, delete or prioritize channels or talk groups in a scan list.


This is a control that cuts off the speaker or headphone when no signal is present, keeping you from hearing the ‘hiss and crackle’. ‘Raising the squelch’ will raise the threshold at which you receive communications.

This may be necessary if you are receiving unwanted messages from other people using the same channel in your vicinity. Remember, channel assignments are not exclusive. ‘Lowering the squelch’ may be necessary if you are having difficulty receiving communications.

Talk Around:

When using a repeater, this feature circumvents the repeater to talk directly to another radio that is close by, to reduce unnecessary airtime through the repeater system.


In conventional radios a frequency is assigned to a channel through programming, one frequency per channel. Channel assignments in a conventional radio can only be changed by re-programming the channel.

In a Trunked radio system all frequencies are in a ‘pool’, the pool is managed by another device. Frequencies are allocated to a radio’s channel dynamically as they are needed.

Once the transmission is complete the frequency is released back into the ‘pool’. This is a much more efficient use of frequencies but requires more sophisticated equipment. There are several types of trunking protocols; LTR®, PassPort®, SmartTrunk®, and IDAS® are the most common.


Logic Trunked Radios (LTR) systems utilize a concept called trunking. This method of channel management gives all users of the system automatic access to all channels. This results in minimum waiting to make a call and the most efficient use of the available channels.

Trunking is controlled by logic circuitry in the mobile transceivers and the repeaters. This circuitry continually monitors the system and generates data messages which update the mobiles and repeaters as to which repeaters are free.


Stands for ‘Project 25′. Is a set of technology standards designed to allow communication between public safety agencies (such as police and fire departments) and developed in response to a lack of communication between different agencies in crisis situations. These radios are not for businesses or personal use.

Do you need more information? Our knowledgeable sales staff can help tailor a solution to your needs.