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Old 12-28-2011, 07:57 AM   #1
oregonrafter
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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/
http://en.wikipedia.org/wiki/Global_...ective_Calling
http://www.boatus.com/mmsi/info.htm

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).
http://www.navcen.uscg.gov/?pageName=mmsi

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:
http://www.uscg.mil/acquisition/rescue21/images/R21nationwide.jpg

More information on Rescue 21 can be found here:
http://www.uscg.mil/acquisition/rescue21/project.asp
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.

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Old 02-20-2012, 02:30 AM   #2
Tar Heel
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Default Re: VHF Radio Q&A, including DSC and Class-D information - updated for 2012

We can "hear you now," Mike. Mike and I met for the first time in Ilwaco the night before my first Tuna trip as captain, on which he thankfully agreed to come along. I had a brand new Standard Horizon HX 851 Hand Held DSC back up radio along with my DSC capable icom main radio, neither were registered and I had not been able to get the main radio to indicate that it was DSC ready, so I had been unable to register it. Mike filled me in and although we weren't DSC capable on that 1st Tuna trip (it was one of those days where we "might" have wanted it) Mike set me on course to get things straightened out and we are now DSC ready on both.

It seems the original installer didn't correctly wire the radio to the GPS, so the "language" the radio and GPS "spoke" weren't the same, so the radio wasn't capable of transmitting GPS coordinates. This is a common oversight, especially for boats that had DSC capable radios installed soon after DSC came into frequent use. Check your owner's manual to "test" (not actually transmit) distress calling and see if you are in fact DSC ready. IF you have a DSC capable radio but it tests to show it's not getting GPS coordinates, chances are it simply isnt wired correctly.

Also, if you have more than one DSC capable radio for a single vessel, both should be registered for the same MMSI #.
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Old 04-30-2012, 04:23 PM   #3
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Default Re: VHF Radio Q&A, including DSC and Class-D information - updated for 2012

This DSC / AIS system should be getting more play than it does.

In essence:
1) Your VHF needs to see a GPS signal to know where you are. (low baud-speed port -- from GPS unit to the VHF.)
2) Your GPS Plotter can likely also display the position of other (AIS) vessels on your GPS screen. (high baud-speed port -- from VHF to the GPS Plotter)

The wiring and setup of communication ports will be the confusing part. For NMEA0183, it's not a 'colors match' schematic. The right "port" is what matters.

Anyway, it's not only the automatic distress call that's of benefit. DSC is the tip of the iceberg.

Not only will your radio tell the Coast Guard where you are:
If we all had MMSI's, and our VHF were linked to our chartplotters, we could all know who is where on the water and boat right to them.

(Anyone can ask and telling someone where you are is optional until a 'distress' goes out.)

If you were in distress and the Coast Guard knew I was closer than they are, I know you'd appreciate my ability to rush straight toward you and offer assistance. But, I can't do it if your DSC and MMSI aren't functioning!
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Old 04-30-2012, 07:14 PM   #4
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Default Re: VHF Radio Q&A, including DSC and Class-D information - updated for 2012

Quote:
Originally Posted by IIonPilgrimg View Post
This DSC / AIS system should be getting more play than it does.

In essence:
1) Your VHF needs to see a GPS signal to know where you are. (low baud-speed port -- from GPS unit to the VHF.)
2) Your GPS Plotter can likely also display the position of other (AIS) vessels on your GPS screen. (high baud-speed port -- from VHF to the GPS Plotter)

The wiring and setup of communication ports will be the confusing part. For NMEA0183, it's not a 'colors match' schematic. The right "port" is what matters.

Anyway, it's not only the automatic distress call that's of benefit. DSC is the tip of the iceberg.

Not only will your radio tell the Coast Guard where you are:
If we all had MMSI's, and our VHF were linked to our chartplotters, we could all know who is where on the water and boat right to them.

(Anyone can ask and telling someone where you are is optional until a 'distress' goes out.)

If you were in distress and the Coast Guard knew I was closer than they are, I know you'd appreciate my ability to rush straight toward you and offer assistance. But, I can't do it if your DSC and MMSI aren't functioning!
In order to prevent confusion, I'd like to state that unless you purchase a VHF radio with built-in AIS or unless you purchase a separate AIS unit, most VHF radios are not capable of AIS function. AIS communicates on a totally different baud rate (38400). The baud rate of DSC is 4800. Most chartplotters will display one or the other, but not both at the same time. For this reason, I have not included AIS in this thread.

Regarding your statement:
"Not only will your radio tell the Coast Guard where you are:
If we all had MMSI's, and our VHF were linked to our chartplotters, we could all know who is where on the water and boat right to them."
This is only partially correct. To view the position of another vessel on your chartplotter (via the VHF/MMSI number) it requires the user to manually enter the MMSI number of the other vessel into the user's VHF radio settings, or to key to a previously stored MMSI number of the other vessel. This is commonly referred-to as a "position request" or "position polling". It is important to note that this is not a totally automatic feature. Again, it requires the user to enter the MMSI number of the other vessel in to the user's VHF radio settings.

There are only two ways you can receive the position of another vessel, one is to have them share their MMSI number and input it in to your radio's settings, and the other is to receive it in a DSC emergency call.

It is also important to note that if another vessel in reception range of your VHF radio makes a DSC emergency call, the position of the vessel (GPS coordinates) and the nature of the distress call will be displayed on the display of your DSC VHF radio. This information does not only get transmitted to the Coast Guard, but will be received by all DSC radios within range of the distress call.
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Old 05-01-2012, 03:00 PM   #5
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Default Re: VHF Radio Q&A, including DSC and Class-D information - updated for 2012

Appreciate the clarification(s).

Yes, I am installing a Standard Horizon Matrix GX2100 AIS+ radio. It's an AIS receiver, not a transmitter, which would have more functions but, also cost significantly more.

I'm looking forward to having a few friends out there, who's MMSI's are in memory for individual polling. But, I'm sensing the system is not being fully utilized and hoping it doesn't go the way of Beta tapes.
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Old 05-01-2012, 04:26 PM   #6
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Default Re: VHF Radio Q&A, including DSC and Class-D information - updated for 2012

Being able to "see" all other fisherman would be great, but not so great if they can see and identify you when you don't want to be seen.

I'm fully OK with the idea of sharing MMSI info among your buddy boats. I haven't done this, but will try it out this season.
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