Two Way Radio Terms and Definitions

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.

A frequency on which a two way radio 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.

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.

Intrinsic safety (IS), also known as FM approved, 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 for a product to be certified as ‘Intrinsically Safe’. Radios meeting this standard have the designation ‘Intrinsically Safe’ or ‘FM Approved’ on their documentation.

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.

Walkie-talkie hand-held radio.

All two way radios 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.

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 radio 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.

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 Re-write: 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.

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.

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 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.