To begin programming a channel on the radio, which button should be pressed?

To program a channel on a radio, the appropriate button to initiate this process is typically designated as the programming button, which in many systems is represented by the "8 PGM" option. This button is specifically designed for programming functions, allowing users to input or modify the settings of the channels on the radio.

When you press the programming button, the radio enters a mode that enables you to set up various parameters such as frequencies, channel names, and other operational settings necessary for effective communication. This function is crucial in ensuring that the correct channels are available and configured as needed for various missions or operations.

The other options can serve different functions within the radio system but do not serve as the primary function for channel programming. Thus, selecting "8 PGM" accurately reflects the needed action to start the programming process for a channel.