Polarity-free PSU filter for ham radio

Many radio amateurs will not fail to recall the chaotic situations that may occur during fielddays or contests, when several radios have to be connected in a hurry and under circumstances less comfortable than those in the shack at home. For instance, many operators may be busy at the same time connecting up the power leads to equipment which is not theirs. In such situations, supply polarity errors may readily occur, with disastrous results.