The Icom M504 is one of the less expensive top-of-the-line radios on the market today. The front panel of this marine VHF houses numerous function pushbuttons, a large dot matrix display screen, and a number of control knobs. Optional add-ons include a remote microphone with controls and a voice scrambler.
Small rotary knobs located on the lower left side of the radio front panel control volume and squelch. A large knob in the center is used for channel selection as well as a variety of menu selections. Channel and transmitter power changes can also be made with microphone pushbuttons.
Overall performance of the Icom M504 transceiver ranked very highly, with one caveat, audio output under performed.
In our transmitter review, the M504 earned an excellent rating for transmitter power stability and a good rating for frequency stability. Receiver sensitivity was rated excellent while selectivity ranked very high with a specification of 80 dB. Audio output was the single data point that was a bit below par, only managing 86 dBA.
The M504 uses a large dot matrix screen that measures almost 3 inches long by 1.5 inches high. Channel numbers are displayed onscreen in large numbers just above a customizable channel comment line. Time and position, frequency group, transmitter power, local/distant, scan tag, and transmit/receive messages are also shown onscreen. Backlighting is adjusted by holding the H/L key and rotating the channel knob. We rated the display screen excellent for viewability.
The M504 features one-button operation of the following functions: power on or off, intercom, shifting between voice and weather channels, changing transmitter power output, running a tag scan, opening the radios’ menu, and selecting receiver attenuation. The last one listed, receiver attenuation, sets the unit for either distant or local reception. In a congested harbor with lots of VHF radio traffic a receiver can be overwhelmed with incoming signals. By setting the unit to local the radio will cut out most of the weak signals thereby improving reception of the stronger nearby signals.
Several other functions on the M504 are operated by using a pair of button pushes. These include: hailer listen back volume, channel group selection, voice scrambler on or off, customization of channel comments, and automatic foghorn on or off. Remaining functions like MMSI number entry, time offset, certain scanning operations, display contrast, and foghorn frequency are set through menus. A low battery icon appears onscreen when input power drops below 12.5 volts. When we increased the voltage back up above 13.2 the warning turned off.
When GPS data is input to the radio boat position and current time are shown onscreen. By pressing and holding the channel selector knob a full screen display including current date, time, position, course, and speed will be displayed.
Digital Selective Calling
The M504 has two separate receivers, one to monitor voice communication channels and another to continuously monitor channel 70 for digital DSC calls; this makes it a DSC Class D marine VHF radio. It can store up to 100 individual or group MMSI numbers with a maximum of 10 character names. A nature of distress tag, selected from a list of 11 items, can be added to a DSC call. This radio will send and receive distress, individual, all ships, group calls as well as transmit and receive position data.
Odds and Ends
The M504 has normal and priority scan modes. Channels are put into memory for scanning by tagging them with the tag pushbutton. Dual Watch monitors channel 16 and another selected channel. Tri-Watch adds a third channel to the scan. In the normal mode channels are scanned in numeric order, when using priority mode channel 16 is checked between each other channel scan.
This Icom marine VHF has a 25-watt hailer capable of producing automatic fog signals as well as normal voice calls when an optional fog horn is installed aboard. It 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 in 50 Hz increments.
The Icom M504 offers very good overall performance, except for the weak audio output, and a long list of value-enhancing features. It carries a 3-year warranty and is waterproof to IPX8 standards.