The top knob turns the radio on and adjusts audio levels.
The P210 is . To change frequencies or privacy codes, you require: Questions about early '90s military radios (Motorola P210)
Operates with approximately 5 to 7 watts of output power, though some regional variants were noted for higher outputs in specific technical discussions. Core Operating Instructions
Typically supports 2 to 8 channels depending on the specific model configuration.