Having two-way radio communication on the trail is basically a necessity. With radio comms we can coordinate our actions and our navigation. It should be obvious that radio communication can be critical for safety reasons.
Various types of two-way radios have been used. In years past CB radio was the natural choice and dominated. With time there has been growing use of ham and GMRS (and “race radios”) due to their superior range.
A run leader will specify the type of radio and the frequency/channel they will use on their run. For the past several years most runs have used ham communications. Generally there should be one channel used during the run. Trying to run two comm channels at once is generally not practical and is not recommended.
Characteristics of the two-way radio types (CB, ham, GMRS, race): Radio Type Characteristics