The Maritime mobile frequency band of 156 - 162 MHz. supports maritime communications worldwide.  Channels used by the maritime mobile service are defined by the International Telecommunication Union.  Communication functions include calling, coast to ship, ship to ship, public correspondence, port operations and safety are supported by these channels.

Due to increased usage the addition of more channels is being considered within the maritime mobile frequency band.  Public Coast Stations have an increased need for additional spectrum.  Also the "Vessel Traffic Services" [VTSs] will need channels just for data transmission.  Analog FM techniques are utilized for normal voice communications, yet channels will be needed for the ever increasing digital information exchanges.

There is a need to find more efficient ways to use the Maritime mobile service band and to increase the number of channels.  Narrowbanding of the Maritime mobile VHF band from 25 kHz. To 12.5 kHz. or even 6.25 kHz. Channel bandwidths may be the answer.  Many considerations are being studied to make this an interoperable system.  The goal is to make "wideband" and "narrowband" radios compatible and to minimize the effects of adjacent channel interference.

Differences in wideband receiver sensitivity for 25 and 12.5 kHz transmitters could cause some wideband radios to have a reduced operating range when communicating with narrowband radios.  The narrowband transmitter has a 2 kHz deviation and the wideband transmitter has a 3 kHz deviation.  Narrowband signals have a lesser amount of energy for wideband receivers to demodulate.

Under 47 CFR 80.371 [c][C] interleaved channels of 12.5 kHz offsets are now permitted on the VHF maritime band for limited operations.  The new interleaved 12.5 kHz channels will go from channel "201" to channel "228" and from channel "260" to channel "287".  These channels are located within the same frequency range as the normal Maritime mobile service.

Radios are being designed with both Narrowband and Wideband capabilities.  Manufacturers of the future 25/12.5 kHz radios could use designs with narrower IF's for better performance without sacrificing receiver sensitivity.  Also these narrowband radios could be designed with separate IF filters which would be used on narrowband channels.

The future of maritime communications is rapidly changing.  Additional channels with 12.5 kHz offsets is already permitted in limited operations.  Manufacturers are already working on guidelines to develop the new "Narrowband VHF" marine radios.

	W. Schneider	DVC-OT	s157125@aol.com
	Daniel Amoroso	BC-OTT	nm3s@prodigy.net
	Joesph Rzucidlo	BC-OTM	jr46@erols.com