What is two-way radio and how do first responders use it?
Able to both receive and transmit radio signals, two-way radio is the most reliable form of voice broadcast communications when everyone involved needs to be able to hear every transmission. This group of users can select different frequency channels to use, so long as they are within the same frequency band (typically VHF, UHF, or 700/800MHz). Sometimes this creates problems between different public safety agencies, such as the police operating on VHF while the fire department is on UHF.
Types of Radio Systems
Direct mode (Simplex): Simple radio-to-radio communication, most reliable for short distances. The main disadvantage is its very limited range and inability to work well in larger buildings.
Repeated: Radio transmissions in a repeated system are rebroadcast with higher power by a repeater, giving improved radio range over a wide area.
Components of Radio Systems
Portable Radios: Having the advantage of being small and portable, these radios come in 3 frequency band versions: VHF, UHF, and 700/800MHz. Typically, public safety radios have the capacity for over 1000 channels, but are limited in their transmission power to between 2.5W and 5W.
Mobile Radios: These radios are permanently installed in vehicles, giving them a higher power (25W to 50W) and a higher range than portable radios.
Repeaters: Basically a radio receiver combined with a powerful radio transmitter, all signals received by the repeater are then rebroadcast with higher power (50w to 300W). Some repeater systems even have multiple transmitters in order to cover a wider geographical area.
Radio Dispatch Console: These systems are used in 911 centers to connect radio dispatchers to the radio system, usually through a hard-wired connection.
Frequency Bands and Channels
VHF Band (150-174 MHz): VHF is typically used by older radio systems, systems that require coverage in wide geographical areas, and systems that require interoperability with marine frequencies. Approximately 15% of public safety agencies use VHF, which is great for outdoor coverage but has poor in-building performance.
UHF Band (450-520 MHz): UHF is a very common band for public safety agencies, used by around 35% of jurisdictions. It gives good performance both outdoors and in.
700 MHz (763-775 MHz, 793-805 MHz): 700 is the most recent addition to the public safety frequency pool. About 10% of jurisdictions use this band for voice communications, however it is expected the band will be adopted across the US in accordance with FirstNet guidelines.
800 MHz (806-815 MHz, 851-860 MHz): 800 is most commonly used for public safety systems, with approximately 40% of jurisdictions using this band. These are newer, mostly trunking systems. The 800 frequency band has good indoor coverage, but not as good outdoor range as UHF and VHF.