Two-way radio systems have been used for business, public safety, and security communications for more than fifty years. Prior to the introduction of cell phones, two-way radios were really the only option when you wanted two-way communications with someone on the go.
Two-way radios consist of two parts, a radio transmitter, and a radio receiver. These two parts are combined into a single unit known as a radio “transceiver”. There are three types of radio transceivers: portable transceivers, mobile transceivers, and base station transceivers. The following is a brief description of each transceiver type:
Portable transceivers, often called “walkie-talkies”, are hand-held units that can easily be carried by the security officer. These units are battery powered and have a self-contained speaker, microphone, and antenna. External microphones and earphones can also be used.
Portable transceivers typically have a range of between one and three miles depending on power, frequency, and the type of obstructions between units. Range within concrete or steel buildings can be considerably less.
Mobile transceivers are larger units that are designed to be mounted in vehicles. Mobile transceivers have an external microphone that makes using the radio while driving more convenient. Mobile transceivers are powered from the the vehicle’s electrical system and typically transmit at a much higher power than that used by portable transceivers. Mobile transceivers also have an external antenna that is usually mounted on the roof or trunk of the vehicle. The combination of a higher transmitting power and an external antenna gives mobile transceivers a much greater range than portable transceivers; typically five to fifteen miles depending on conditions.
Base Station Transceivers
Base station transceivers are designed to be mounted at a fixed location, such as at the security command center. Base station transceivers typically operate at high power levels and use an external antenna mounted on the roof of the building. Base station transceivers can be provided with desktop microphones and speakers that can allow use of the radio from multiple locations in the security command center.
The typical security department would probably use a combination of transceiver types; portable transceivers would be carried by security officers, mobile transceivers would be used in security patrol vehicles, and a base station transceiver would be used at the security command center.
Two-way radio systems are available in several different frequency ranges. VHF high band (130 -174 MHz) and UHF (400 – 512 MHz) are the frequencies most commonly used for security purposes. Most security organizations use conventional analog two-way radio systems, although some very large organizations may use digital or trunked radio systems.
Many campuses are so large that they exceed the limited range of a portable two-way radio transceiver. To solve this problem, radio repeaters are often used. Radio repeaters are mounted at a high-point on the campus (such as at the top of a building or water tower) and extend the range of signals by receiving and retransmitting them. A repeater mounted in a very high place (such as on a mountaintop or high-rise building) can often allow portable transceivers to cover an entire city or county.
Some buildings are so densely constructed that they block out radio signals, preventing communications through more than one or two floors. To solve this problem, distributed antenna systems can be used within the building to pickup and and distribute signals between floors. These systems often use “leaky coax” type antennas installed above the ceilings.
Many large organizations may need to use a combination of both radio repeaters and distributed antenna systems to provide reliable two-way radio system coverage throughout their entire campus.