A diode is in series in the positive power lead to a transceiver. What is its purpose?

A diode is a semiconductor device that acts like a one-way valve for electricity, allowing current to flow in only one direction. When placed in series with the positive power lead of a transceiver, it acts as a directional gatekeeper. If the power supply is connected correctly, the diode is forward-biased and allows current to power the radio. If the power supply is accidentally connected backward (reverse polarity), the diode becomes reverse-biased and blocks the current entirely. This simple mechanism protects the delicate internal components of the transceiver from being destroyed by backward voltage. Distractors like overcurrent protection are incorrect because preventing too much current is the job of a fuse or circuit breaker.