VHF Radio Q&A, including DSC and Class-D information - updated for 2012 - www.ifish.net
Leave no Dog Behind

Go Back   www.ifish.net > Ifish Fishing and Hunting > The Salty Dogs

Thread Tools Display Modes
Prev Previous Post   Next Post Next
Old 12-28-2011, 07:57 AM   #1
oregonrafter's Avatar
Join Date: Dec 2008
Location: NW Portland
Posts: 1,813
Default VHF Radio Q&A, including DSC and Class-D information - updated for 2012

I have updated and condensed the information in the old thread on this subject.

Buying, selling or installing a VHF Radio?
If you are considering purchasing, selling or reinstalling a VHF radio in the near future, this information is very important to consider.

As of March 25th, 2011, the FCC has made it illegal to buy, sell, or install some DSC capable VHF radios. After this date, all VHF radios must not only be DSC capable, but must also be Class D compliant.

This is a quote from the US Coast Guard website:
Beginning on March 25th, 2011, the Federal Communications Commission will prohibit the manufacture, importation, sale and installation of fixed mounted (non-portable) digital selective calling (DSC) equipped marine radios that do not meet the requirements of International Telecommunications Union (ITU-R) Recommendation M.493-11 or higher, and in the case of Class D VHF DSC equipment only, International Electrotechnical Commission (IEC) International Standard 62238. Therefore, after March 25, 2011, radios built to RTCM Standard SC-101 can no longer be manufactured, imported, sold or installed; however, previously-installed radios meeting the older standard may continue to be used.
This, and more information can be found at the USCG website; here: http://www.navcen.uscg.gov/?pageName=mtDsc
What is "Class D"?
Class D equipment is specifically designed for recreational vessels. It provides VHF DSC distress, urgency and safety as well as routine calling and position polling. Class D equipment includes a dedicated channel 70 DSC receiver, so you will never miss a DSC call.

More on DSC (and Class D) here: http://www.vhf-dsc.info/

After you buy a Class D VHF radio...
You must do a couple things in-order for it to work correctly.

1. You need to register for an MMSI number in order for the Coast Guard to be able to identify your boat (required).

2. Your DSC capable fixed-mount VHF radio must be connected to an external GPS source for DSC function to work properly. This can be a separate GPS antenna, or a chartplotter/GPS unit (which has a built-in antenna).
If you have a non-Class D DSC radio, will you need to upgrade?
Users of RTCM-SC-101 compliant DSC radios that are not Class D, will not be required to upgrade. This new specification is only for insuring that all radios that are sold or reinstalled after March 25th, 2011 are Class D.
What's the difference between RTCM-SC-101 DSC VHF compliant radios, and Class D VHF DSC radios?
Class D radios have a dedicated receiver for channel 70. All DSC calls are transmitted on channel 70, so having a dedicated receiver means that there is no chance for a Class D user to miss a call.

I found this explanation in an article at the US Power Squadron's website:
There are generally two classes radios sold in the US. fall into. Class D was developed to provide DSC capability for VHF marine radios carried by recreational boaters. In order to get production going in the US a simplified version of class D was developed – designated SC-101.

These new DSC radios use channel 70 for the transmission of digital information. The less expensive models (typically meeting the SC-101 spec.) have one receiver, and operate by scanning between the normal voice channels and channel 70. If your radio is in use (either transmitting or with the receiver squelch open) it will not receive a digital call. The class D radios have two receivers – the second is committed to receive only channel 70. In this way you are much less likely to miss a call, it is of significant advantage to buy a radio that meets the class D spec.
The source of the above quote can be found here: http://www.usps.org/national/safety/SafetyBulletinFeb2007.pdf

Non Class D DSC radios allow you to broadcast a distress signal on channel 70. The new Class D radios effectively minimize the chances of other DSC radio users from missing your distress call if they are simultaneously using their radios at the same time your distress call is initiated.

All DSC radios (whether Class D or non Class D) transmit distress calls the same way.
Are all new VHF radios Class D compliant?
If you purchase a fixed-mount VHF radio from a reputable source, then it will probably be Class D compliant, as it is now illegal for anyone to sell non-Class D radios. Some smaller retailers may not be aware of this regulation change, so it is always good to check the model number to be sure. Be aware that some model names have remained the same through this change, so it is important to cross-reference the model number (not just the model name) of the radio you are considering.

All portable/hand-held VHF radios being sold today are still not Class D Compliant, and are not yet required to be compliant by the FCC. Some handhelds, however, are DSC capable.
How do you know if your current VHF radio has DSC?
The simple answer: If your radio has a button that is covered by a bright red, see-through plastic cover, then it has DSC (Digital Select Calling) capability. Note that DSC does not work “out of the box”. It requires the owner/installer to follow some simple steps for it to be enabled. Refer to: ‘After you buy a Class D VHF radio’ of these instructions for details. Please note that not all fixed-mount DSC VHF radios are Class D compliant, and must be in order to be installed in any vessel.

A few manufacturers are beginning to make hand-held radios that are currently available with built-in GPS, and so they are capable of Digital Select Calling. The major advantage to these newest handhelds, is that you can automatically communicate your digital coordinates – Important if you have no EPIRB or PLB, or if you want redundant forms of location-sending devices.
How do you know if your current radio is a Class D radio?
Typically this information is not shown anywhere on the radio, so you’ll need to do a little research. Consult your owner’s manual or look-up the model number (not the model name) on the internet. If your radio was purchased prior to March 2011, it may not be Class D compliant.
What happens when you push the red button?
When the DSC (Digital Select Calling) button under the red flap is pressed, digital information (not audio) is sent from your VHF radio to the Coast Guard, via the Rescue 21 system. This digital information includes your MMSI number and your coordinates. The Coast Guard can then look-up detailed information that you supplied when you registered-for (and received) your MMSI. Also after the button is pressed, your radio will automatically switch to channel 16, so the Coast Guard and other VHF radio equipped vessels may hear your calls and communicate with you. If their radios are Class D compliant, other radio operators/vessels will automatically hear your calls after the red button is pressed on your radio.
Important note: If your vessel is more than 25 nautical miles from the nearest Rescue 21 station, the Coast Guard may not receive your distress call. However, if you are out-of-range, it is still important to press the button if you are in distress. Why? –Because other vessels within reception range will likely hear your distress call, and may be able to communicate with the Coast Guard for you, and may be able to offer direct assistance before the Coast Guard can reach you.
What is the “Rescue 21” system, and is it available in your area?
Rescue 21 is the system communication and implementation that the Coast Guard uses for monitoring distress calls (including DSC calls), as well as to aid in homeland security.
This description is from Coast Guard website:
Rescue 21 is the United States Coast Guard’s advanced command, control and communications system. Created to improve the ability to assist mariners in distress and save lives and property at sea, the system is currently being installed in stages across the United States.

A map showing all existing Rescue 21 stations is located here:

More information on Rescue 21 can be found here:
Still Confused?
The Coast Guard has a comprehensive tutorial video on VHF/DSC radio operation. It covers the "Rescue 21" system, and how it works in conjunction with DSC emergency calls. It also covers VHF equipment selection (including Class A, Class D, and the now obsolete SC-101), equipping your boat with necessary peripheral equipment, installation, programming MMSI, and use of your radio in conjunction with DSC. If you have any questions in your mind how VHF/DSC works, I highly recommend you watch this video from beginning to end. It is likely that even if you use VHF regularly, you're going to learn something you didn't know.

The video is entitled, "Can you hear me". You can view it here: http://www.boatus.com/foundation/dsc...T.mc_id=400090 The total length of the video is about 37.5 minutes.
If you do nothing else, at least watch this video.
It contains a basic overview of the information that is contained in this tutorial, as well as some other interesting information.

oregonrafter is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Cast to

All times are GMT -8. The time now is 10:16 PM.

Terms of Service
Page generated in 0.22006 seconds with 21 queries