The radio's receiver is no slouch from a performance perspective, with excellent specifications of 80 dB (typical) for intermodulation rejection, adjacent channel selectivity, and 0.22 uV (typical) high sensitivity. The result is a receiver that's powerful enough to catch a weak signal even between two strong signals, making it much less likely that you'll miss important transmissions. The extra-large speaker, meanwhile, is mounted into a well-spaced housing that delivers a bigger sound than the specified 4.5 watts of output power. As a result, both casual messages and urgent distress calls come through loud and clear even when the engine is roaring.

The IC-M504 offers several scanning modes, including an auto scan function that starts scanning whenever no signal is detected, a traditional scan mode that searches through all the tag channels in sequence, a priority scan mode that does the same but also monitors the distress channel (number 16), and a weather alert option that immediately switches the radio to the appropriate weather channel when a storm warning comes through. Users will also dig the Dual Watch and Tri-Watch functions. The former lets you communicate on a channel of your choice while also keeping an eye on emergency channel 16, while the latter monitors two channels--channel 16 and another channel--while receiving a third channel. The pair of "watch" modes guarantee that you won't miss an important emergency call from a distressed boater while your attention is otherwise engaged.

As with other high-quality fixed-mount VHF radios, the IC-M504 comes with built-in Class D Digital Selective Calling (DSC), which lets you constantly monitor channel 70 or send a formatted distress message in an emergency. DSC activates an instantaneous, continuous "mayday" signal that identifies your vessel and time stamps the message. And when connected to a NMEA-enabled GPS receiver, your radio can easily send the position data of your boat or determine another vessel's location and then display it your LCD screen or the GPS itself. The polling function even checks whether a specific ship is in your communication range.

And by adding the optional CommandMic III microphone (sold separately), users can control all available functions of the IC-M504 from a remote location, such as from the deck or the fly bridge. The CommandMic III--which includes a multifunction jog dial for quick and easy access to the settings--works from up to 60 feet away, and handles such functions as distress calls, DSC calls, squelch adjustments, foghorn signals, and more. It even doubles as an intercom, making onboard communication easier than ever.

Other details include a PA function (when connected to a hailer horn or external speaker), an RX speaker function, four foghorn patterns, instant access to channels 16 and 9, compatibility with the UT-112 voice scrambler (sold separately) for communication privacy, and a sleek black housing. The IC-M504 measures 6.5 by 4.34 by 4.84 inches (W x H x D) and is backed by a three-year warranty.

What's in the Box
IC-M504 radio, hand microphone, mounting bracket kit, spare fuses, DC power cable, user's manual.

The CommandMic comes with 19.8 feet of extension cable, a microphone hanger, and a mounting base for the cable connector (the connection point is nearly flush with the mounting surface). And crucially for a marine microphone, the unit is waterproof to JIS 7 standards, meaning you can submerge it in 1 meter of water for up to 30 minutes without damaging the electronics. The HM-157B, which boasts a sleek black housing (an alternate white version is available), measures 2.34 by 4.78 by 1.19 inches (W x H x D) and is covered by a three-year waterproof warranty.

What's in the Box
CommandMic microphone, extension cable, microphone hanger, mounting base, user's manual.