Style 399-1M VHF 6dB, Collinear Phased 5/8-wave with two coaxial chokes to suppress cable radiation. The 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. Brass and copper elements, Chrome-plated brass ferrule with standard 1"-14 thread, Aluminum sleeve for mast mounting, Suggested mount: 1-1/4" U-bolts are supplied. The 399-1M can be strapped to a larger mast using steel banding (not supplied), Two sections: Base 75"; Tip 39" UPS shippable. VHF Marine band frequency, 50 ohms impedance, 6 dB gain. Vertical Polarization, with omni-directional radiation pattern.