They all ( well most ) can & cover,am/fm & trunked ex: LTR & what not. basically if it isn't trunked it will be AM/NFM /FM or P25. I Suggest you read up on the read up on the basics of scannng. Look heere & start reading Main Page - The RadioReference Wiki
Scanners generally default to a particular modulation type for a particular band segment because that is the prevalent modulation in use in that segment. Most can be set to demodulate others.