Fixed-mount VHF radio with DSC

Communication

The main radio on most boats: for calling other boats, marinas, bridges and the Coast Guard, and for hearing weather. The DSC part adds a red DISTRESS key that sends your boat's ID number (MMSI) and, if the radio has a GPS feed, your position, with one press.

How it works

Marine VHF travels roughly line of sight, so antenna height matters more than wattage; the Coast Guard describes VHF range as generally 5-10 miles, and at least 20 miles to one of its stations. Fixed radios send up to 25 watts, with a 1-watt low setting. DSC is a digital calling system on channel 70. Every DSC call carries your nine-digit MMSI; a distress alert also carries latitude and longitude, but only if the radio has its own GPS or is wired to one.

Using it

Underway, leave the radio on channel 16 when you aren't talking on another channel. FCC rules let recreational boats use channel 9 for calling instead, but the Coast Guard suggests 16 because it announces warnings and urgent broadcasts there.
Use 16 only to make contact or for emergencies, then switch to a working channel. Recreational working channels include 68, 69, 71, 72 and 78A (72 is boat-to-boat only).
Channel 13 is the bridge-to-bridge channel for passing arrangements with ships and for many bridges and locks. Keep it short; fixed radios drop to 1 watt there automatically.
Coast Guard safety broadcasts are announced on 16 and then read on channel 22A, which newer radios label 1022. Keep the radio in its USA channel mode in US waters so 22A works the US way.
Try 1 watt first for nearby stations and switch to 25 watts only if needed. The FCC asks you not to call the same station for more than 30 seconds, and to wait 2 minutes before calling again.
To send a DSC distress alert, lift the cover on the DISTRESS key, pick the kind of emergency if there's time, then press and hold until the radio confirms. Follow up at once with a spoken MAYDAY on channel 16; the Coast Guard says missing voice follow-up is the biggest DSC problem.
If you set off a distress alert by mistake, don't switch the radio off, because many radios resume the alert when powered up. Use the radio's cancel menu to send a cancellation, then tell the Coast Guard on 16 your boat name and MMSI.
Check DSC with a Test Call to the Coast Guard group number 003669999, never with the DISTRESS key. The screen should show the answering station's number. For voice radio checks, use channel 9, not 16.
If you receive another boat's DSC distress alert, don't relay it by DSC. The FCC says listen on 16 for 5 minutes; if no coast station answers, acknowledge by voice and tell the Coast Guard what you received.

Rules & requirements

Licence (FCC, 47 CFR 80.13(c)): a recreational boat that isn't required to carry a radio, doesn't go to foreign ports and doesn't talk to foreign stations is licensed by rule for VHF, AIS, EPIRB and radar. No individual ship station licence is needed.
Foreign ports (FCC): if you visit Canada, Mexico, the Bahamas or any foreign port, you need an FCC ship station licence (Form 605, 10-year term) plus a Restricted Radiotelephone Operator Permit (no test, valid for life).
MMSI (FCC): a DSC radio must have a nine-digit MMSI programmed before you transmit with it. USCG NAVCEN says every radio on the boat uses the same MMSI, except AIS-SARTs and handhelds not kept for that boat.
Where to get an MMSI: boats with an FCC licence get one with the licence. Unlicensed, US-only recreational boats can get a domestic MMSI from BoatUS, United States Power Squadrons or Shine Micro (FCC and USCG NAVCEN lists). Domestic MMSIs aren't valid for foreign voyages.
Watch (FCC 47 CFR 80.310): when underway and not using the radio, keep a watch on channel 16. Recreational boats may use channel 9 instead for calling, and a VHF-DSC radio may keep its automatic watch on channel 70 or a listening watch on 16.
Power (FCC 47 CFR 80.215): ship VHF is limited to 25 watts and must be able to drop to 1 watt. Fixed radios made after January 21, 1987 must switch to 1 watt automatically on channels 13 and 67, with a hold-to-override switch. Handhelds are exempt from the automatic drop.
Channel use (FCC 47 CFR 80.371, 80.373): 16 is for distress, safety and calling; 70 is digital-only with no voice; 13 is for navigation safety at 1 watt. Use only the channels the FCC table assigns to the kind of message you're sending.
Bridge-to-bridge watch (USCG, 33 CFR 26): power-driven vessels 20 m (about 65 ft) and longer, and towing vessels 26 ft and longer, must also keep a watch on channel 13 in US waters, using two receivers rather than a scanner.
False distress calls: sending a false or hoax MAYDAY, including a fake one to get a radio check, can be prosecuted as a felony under 14 U.S.C. 85, the Coast Guard warns, with a fine and the cost of the search.

Looking after it

Each season, unscrew the coax plug (usually a PL-259) at the back of the radio and at any deck or mast joint. Look for green or black corrosion, water, salt or a loose centre pin, and clean or replace as needed.
Keep outdoor connectors sealed against water, and keep the antenna at least 3 ft from other antennas and metal and at least 3 ft from the radio itself, as the antenna maker advises.
Coax loses signal along its length. The maker's figures for 50 ft: about 3 dB for thin RG-58, 2 dB for RG-8X, 1 dB for RG-213. On a long run up a mast, the heavier cable wastes less of your power.
Clean a fiberglass antenna with mild soap and water only. If the fiberglass frays, the maker suggests sealing it with polyurethane or a lead-free, non-metallic paint.
Once a season, open the radio's position screen and confirm it shows your current position and time. Some radios beep regularly when no GPS data is arriving.
Check the fuse and power leads. If a radio blows its fuse the moment it's connected, one maker's manual says to suspect reversed power wires.
Never key the mic with the antenna disconnected; radio makers warn this can damage the transmitter.

Troubleshooting

Poor range, or other boats say you're weak or broken up

Make sure you're on high power (25 W) and not on channel 13 or 67, which drop to 1 watt automatically.
Send a DSC Test Call to 003669999. The Coast Guard says a radio that gets an acknowledgement should work acceptably on voice too.
Check each coax connector from the radio outward for corrosion, water or a loose pin, then look over the antenna and its mount for cracks or damage.
If reception is noisy, test for LED interference: tune a quiet channel, set the squelch just closed, then switch LED lights on. If the radio opens up, the LEDs are raising the noise level (USCG Safety Alert 13-18).
Have a shop measure output power and antenna SWR with a meter; high SWR usually points to cut or damaged coax, nearby metal or a badly fitted PL-259.

Radio won't transmit at all

Make sure you aren't on a receive-only channel: the weather channels (WX) can't transmit, and channel 70 carries DSC data only.
Check the fuse and the power connections at the radio and at the panel.
Check the microphone plug and try again; if the radio has a second station or remote mic, try that one.
Check the antenna connection and coax as for poor range before keying again.

DSC distress or position screen shows no position

Look at the radio's GPS/position screen to confirm whether any position data is arriving.
If the GPS is wired by NMEA 0183, check that the plotter's data OUT wires go to the radio's GPS IN wires (positive to positive, negative to negative).
Check the plotter is set to send position sentences on that port. One maker's radio wants RMC, GGA, GLL or GNS at 4800 baud with no parity.
On an NMEA 2000 boat, check the radio appears on the network and sees a position source.
As a stopgap, many radios let you type your position in by hand for a distress alert.

DSC menus won't work or the radio asks for an MMSI

DSC functions don't work until an MMSI is programmed; check the radio's MMSI setup screen.
If an MMSI is present, confirm it's yours and not the previous owner's (see Buying used).

Buying a boat that has one

Look for a red DISTRESS key. Radio models certified before mid-1999 generally have no DSC at all.
Read the MMSI stored in the radio. If it's the previous owner's, it must be transferred to you or replaced; two boats must never share an MMSI. NAVCEN publishes the number blocks that show whether it came from BoatUS, USPS, Shine Micro or the FCC.
Many radios accept an MMSI only once; changing it needs the maker or a dealer. Budget for that if the stored number is wrong.
If the MMSI was issued by Sea Tow, NAVCEN says Sea Tow has left the MMSI program and moved its accounts to the United States Power Squadrons, so update the registration there.
Check whether GPS position actually reaches the radio. Plenty of 1999-2010 radios have a GPS input that was never wired.
Radios sold since 2011 must have a DSC Test Call feature. Older sets may not, and old models may no longer be supported by their makers.
If the seller had an FCC ship station licence, it doesn't pass with the boat. The FCC MMSI can be reused only after the seller cancels that licence.
Do a DSC Test Call and a voice check with a friend at a known distance, and inspect the coax and antenna, which may be as old as the boat.

Sources (19)

fcc.gov · fcc.gov · fcc.gov · ecfr.gov · ecfr.gov · ecfr.gov · navcen.uscg.gov · navcen.uscg.gov · navcen.uscg.gov · navcen.uscg.gov · navcen.uscg.gov · navcen.uscg.gov · navcen.uscg.gov · navcen.uscg.gov · navcen.uscg.gov · boatus.com · standardhorizon.com · shakespeare-marine.com · www8.garmin.com

General guidance for recreational boaters, researched from the sources listed and written in our own words. Your equipment manuals, local knowledge, the Navigation Rules and a qualified instructor come first.