The Icom M304 is this manufacturers entry level fixed mount marine VHF radio. It is compact in size and performs basic transmit, receive, and DSC operations without the fuss and expense of unwanted features.
One-button operational features are limited to: making a DSC distress call, selecting the call channel or 16 or 9, turning scan on or off, and turning Dualwatch or Tri-watch on or off.
Channel selection is made with up/down arrow buttons on the front panel or microphone.
High or low transmitter power is set with a pushbutton on the microphone. Pressing both arrow keys simultaneously sets the channel group.
Several other functions are operated by a combination of button pushes. These include, programming the units MMSI number, customizing channel comments, programming the call channel, locking the microphone buttons, and using the AquaQuake function. This last one uses the arrow buttons and the on switch to turn on a low frequency tone to clear water from the speaker. Once you release the arrow keys the tone stops and normal operation resumes.
A low battery warning scrolls across the screen when input voltage goes below 12.2 volts.
Small rotary knobs located on the right side turn the radio on or off and volume and squelch levels. Scan type, weather alert, selection of dual or tri-watch, and a few other functions are set by entering a mode programming menu.
Performance of the Icom M304 transceiver was below par when compared to previously tested Icom radios. In our transmitter review, it earned an excellent rating for transmitter power stability but only a fair rating for frequency stability. It drifted slightly off frequency during our cold temperature testingstill it remained well within industry and governmental specifications. Receiver sensitivity was rated excellent while selectivity carries a specification of greater than 70 dB. Audio output was good at 90 dBA.
The M304 has a smallish screen that measures 1.6 inches long by 1.0 inches high. Channel numbers display in large block-style numbers mid-screen. Icons for tag channels, transmit and receive, and channels comments are on either side. Channel comments scroll across a five-character line at the bottom of the screen. Backlighting is adjusted to one of four levels by holding the Scan key and pressing the up or down arrow. We rated the display screen good.
The M304 can listen for signals on channel 16 while monitoring other channels via Dualwatch and Tri-watch, which ever mode is selected is annunciated onscreen. Scanning several channels at once is accomplished via normal or priority scanning. Normal looks at each channel on order while priority checks channel 16 between other channels. Channels are selected for scanning by tagging them with a button push.
Digital Selective Calling
The M304 is classed as an SC101 radio for DSC operations. That means it has a single receiver listening to both voice communications and DSC digital data coming in over channel 70. This radio will send and receive distress, individual, all ships, and send and receive position data. It can store up to 30 individual MMSI numbers with a maximum of 5 character names.
Outside of one category the Icom M304 performed well on our testing. Add in that the fact that this marine radio carries the Icom brand name, their high standards for build quality, all packaged into a compact size and you’ll see why so many of these marine radios have found their so many recreational boats.