What is the term for a radio that transmits and receives on two different frequencies?

The term for a radio that transmits and receives on two different frequencies is known as duplex. In duplex communication, two separate channels are utilized, allowing simultaneous transmission and reception. This provides a more efficient and effective means of communication, especially in scenarios such as firefighting, where clear and timely exchanges of information can be critical.

In contrast to duplex, simplex systems operate on a single channel for communication, allowing only one party to transmit at a time. Half duplex systems also use a single channel, but they allow for two-way communication, where one party transmits while the other listens, although not simultaneously. Multiplex refers to a system that combines multiple signals into one channel, but it does not specifically address the distinct nature of transmitting and receiving on separate frequencies. Therefore, duplex is the correct term for radios that can simultaneously handle different frequencies for sending and receiving.