Style 399-1M VHF 6dBCollinear Phased 5/8-wave with two coaxial chokes to suppress cable radiationThe Style 399-1M is the same as the 399-1, but it has a special sleeve for mast mounting. A professional quality antenna in a compact package. This extra-duty antenna combines strength and performance for use where you really need the efficiency of a large antenna, but don't have room for one.