What type of radio system allows multiple transmitter sites to transmit on the same frequency at the same time?

The type of radio system that enables multiple transmitter sites to transmit on the same frequency simultaneously is a simulcast radio system. This technology is designed to enhance coverage and ensure that messages are broadcast over a wider area without the need for multiple frequencies.

In a simulcast setup, the same audio signal is transmitted by different transmitters located at various sites. This is particularly effective in urban environments where obstacles such as buildings can obstruct signals. By using simulcast, users can receive clearer and more reliable communication, making it an essential feature for emergency response and public safety communications.

Conventional radio systems generally operate on a single frequency and do not support simultaneous broadcasts from multiple sites. Trunked radio systems utilize a pool of frequencies and allocate them dynamically, but they do not inherently allow for the simultaneous transmission of the same signal across multiple transmitters. Digital radio refers to a broader category of radio technology focusing on digital encoding for transmission, which doesn't specifically address the capability for simultaneous transmission from various locations. Therefore, the correct answer highlights the unique capability of simulcast radio to provide extensive coverage and improve signal reliability through coordinated broadcasting from multiple sites.