Low band radio systems for law enforcement, like those used by the North Carolina State Highway Patrol (NCSHP), operate on a semi-duplex model for car-to-base and base-to-car communication. This means the base station transmits and receives on separate frequencies, but the received audio isn’t rebroadcast. To hear mobile unit traffic with a scanner, you’d need a strong low band antenna and be in close proximity to the transmitting vehicle.
Car-to-car communication, often called “3 way” mode, utilizes a simplex frequency—the same one used for base-to-car transmissions. This allows direct communication between patrol cars without relaying through the base station. For instance, Troop F uses 42.600 MHz for both base-to-car and car-to-car communication, while 42.660 MHz is used for car-to-base transmissions. Each communication center has its designated frequency pairs for low band communication, which can be found in radio frequency databases. In addition to these pairs, there’s a simplex Events channel, Channel 19, used frequently in certain areas.
The older low band system is gradually being replaced by the 800 MHz trunked radio system known as VIPER. This newer system offers improved coverage and features. Troop A and parts of other troop zones have already transitioned to VIPER, with the expectation that the entire state will eventually follow suit, rendering the low band system obsolete. While specific NCSHP scanner freq information for car-to-car communication on VIPER isn’t provided here, understanding the transition from low band to trunked systems is crucial for anyone monitoring law enforcement radio traffic.
