The Icom M604 is the most expensive and sophisticated marine VHF radio produced by well-known radio maker Icom. This top-of-the-line marine VHF features an alphanumeric keypad, a large dot matrix display screen, and very good overall performance ratings.
The M604 can connect to as many as two optional remote microphones, can operate as part of an intercom system, as well as be coupled to an optional voice scrambler.
The M604 performance ranked with the best of the marine VHF radios I have tested. In our transmitter review, the M604 power output was stable over the entire range of tests and earned good rating. Frequency stability also tested well and garnered a good rating too. We rated receiver sensitivity excellent while selectivity ranked high at greater than 80 dB. Audio output was rated excellent with sound pressure levels hitting an ear splitting 97 dBA.
The Icom M604 uses a dot matrix screen almost 3 inches long by 1.5 inches high to display data. It shows channel numbers in large block letters just above a customizable channel comment. Time and position, frequency group, transmitter power, local/distant, scan tag, and transmit/receive icons are also shown onscreen. We rated the display screen excellent.
A single button push allows the user to select transmitter power level, toggle between weather and voice channels, and make a quick 16 channel selection. Pressing two pushbuttons at the same time switches between US, International, and Canadian channels. Volume, squelch, and channel selection are controlled with rotary knobs. Current time and position are normally displayed onscreen when GPS data is input to the radio. Boat course and speed can also be displayed.
Special functions are operated by coupling the function key (F) with an alphanumeric key. For example, hitting the F key followed by the 3 key activates screen backlighting adjustment. Once selected backlighting is adjusted up or down by turning the channel selector knob. Other keys control scanning, channel selection, receiver local/distant setting, hailer, automatic fog signals, optional intercom, and optional voice scrambler.
A low battery message will appear onscreen when input power drops below 12.8 volts. Increasing the voltage back above 13.2 turned off the warning.
Digital Selective Calling
The M604 is designated a DSC Class D radio and can store up to 100 other individual or group MMSI numbers with a maximum of 10 character names. As many as 20 incoming distress and 20 other incoming messages can also be stored. A nature of distress tag, selected from a list of 11 items, can be added to a DSC call. This radio will make distress, individual, all ships, and group calls as well as transmit and receive position data.
Odds and Ends
Dual Watch scanning is turned on with the function key and the dual button. The mode scans channel 16 and any other selected channel. Tri-Watch adds a third channel to the scanning mix. In the normal mode channels are scanned in numeric order, when using priority mode channel 16 is checked between each other channel scan. On this Icom VHF channels are tagged to be included in a scan or untagged to be removed using a dedicated pushbutton.
Automatic fog signals are selected by pressing the function key followed by the fog key. The unit can sound signals for: power vessel underway, vessel underway but not making way, sailing vessel underway (this one can also be used for several other vessel conditions), and vessel under tow. Foghorn tone is adjustable from 200 to 850 Hz.
This radio has very good overall performance and a long list of user-friendly features. If you want the best from Icom aboard your boat the M604 is it. It carries a 3-year warranty and is waterproof to IPX7 standards.