Moderated Discussion Areas
  ContinuousWave: Small Boat Electrical
  Class D or No Class D VHF radios

Post New Topic  Post Reply
search | FAQ | profile | register | author help

Author Topic:   Class D or No Class D VHF radios
WT posted 10-16-2007 07:38 PM ET (US)   Profile for WT   Send Email to WT  
I need another VHF because my ICOM 402 has been having problems receiving calls.

My understanding is that class D radios monitor channel 70 FULL time. Some of the newer non-class D radios also monitor channel 70 but not full time, so in theory you could miss a DSC call. Both radios receive and send gps data and they both plot locations of your callers.

My current radio is the "normal" size and is flush mounted. I've noticed that the Class D radios are larger than the "normal" size by about 1.25 inches in height. I'm not thrilled about having a larger hole cut out of my console for the Class D VHF.

Class D radios: ProdCatID=83&encProdID=0337C04EDEA920DFAA2098EB3EE8932B&DivisionID=3& isArchived=0

Non-class D but monitors channel 70 and does position request and reporting with an external GPS:

I know this DSC stuff isn't ready for prime time. So would you guys choose Class D or non-class D radios if having to buy a radio today?

Oh yeah, there's about a $200 price difference between the class D and non-class D radios.



Chuck Tribolet posted 10-16-2007 08:01 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
None of them display the position of your caller. Some will
display the position of someone to whom you have sent a
position request call, and to which their radio has replied
with their position (not all radios will reply, and they can
often be programmed to not reply without human intervention
(I guess to keep fishing holes secret).

I'm not sure sending and receiving position request (don't
confuse this with sending a digital mayday) is a requirement
for Class D, though most if not all of the high-end DSC
radios have it.

Every DSC radio I've ever seen could send and receive a digital

The non-class D radios scan Ch 70. They aren't listening on
70 when transmitting or receiving. In my area, the voice
channels I scan are pretty quiet (well, except for the first
couple of weeks of salmon season) so it probably doesn't make
a lot of difference for me.


Chuck Tribolet posted 10-16-2007 08:02 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Also, try a different antenna (I've got one you can borrow
if we can figure out how to get it up there to you), and
check Icom's flat rate repair price if that doesn't help.


jimh posted 10-16-2007 08:38 PM ET (US)     Profile for jimh  Send Email to jimh     
If there is a $200 difference between a Class-D radio and a non-Class-D radio, then the non-Class-D radio would be free and you'd get $75 cash for taking it!

You can get a nice Class-D radio from Standard-Horizon for about $125, the GX1500S. It is a bit larger than some of the ICOM radios.

WT posted 10-16-2007 09:08 PM ET (US)     Profile for WT  Send Email to WT     
Thanks Jim.

On the Standard Horizon website the only class D radio is the GX5500S. The rest of the units do not indicate class D classification.


WT posted 10-16-2007 09:15 PM ET (US)     Profile for WT  Send Email to WT     

I was wrong about the Standard Horizon GX5500S being the only class d radio. I didn't read the fine print of the other radios. :-O


BellBoyBob posted 10-17-2007 08:46 AM ET (US)     Profile for BellBoyBob  Send Email to BellBoyBob     
Thought I would chime in. The Icom 402 - a radio I have owned - is a class D DSC radio with NMEA in only. It cannot plot a caller's position on a GPS plotter. This is the reason I replaced it with the Standard Horizon GX3000S class D DSC radio. This one has a hailer and NMEA in and out. It plots on a GPS. The 402 WILL give a DSC caller's position (lat \ lon) on the radio's lcd and I had it in for service before selling it to remove the MMSI number and check on a faulty mic wire. The service was great and the warranty repair went smoothly and quickly.
This new technology in marine radios neccessitates very careful researching before purchase. Jim's suggestion of the GX1500S would suit your needs perfectly. It has all of the features of the Icom 504, is built as well and is MUCH cheaper to buy online. My GX3000S was $169 online
bluewaterpirate posted 10-17-2007 10:46 AM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
The ICOM 402 is not a Class D VHF DSC radio. It has DSC capability but only has one receiver. The 402/402a/402sa/502 can only receive NMEA data from a GPS and the 422/502A/504/506 can send and receive NMEA data.


BellBoyBob posted 10-17-2007 11:29 AM ET (US)     Profile for BellBoyBob  Send Email to BellBoyBob     
Oops, you are right. Does the fact that the 402 can only receive and not transmit polling info to the GPS define its status as not being Class D?
bluewaterpirate posted 10-17-2007 12:18 PM ET (US)     Profile for bluewaterpirate  Send Email to bluewaterpirate     
A true class D radio has two receivers has nothing to do with NMEA input/output. There you go.


jimh posted 10-18-2007 09:32 PM ET (US)     Profile for jimh  Send Email to jimh     
I do not believe that the ICOM M-402 is qualified as a Class-D DSC Marine Band Radio. ICOM was one of the last manufacturers to bring a Class-D radio to market. Only their most recent models have earned that rating.

My article in the REFERENCE section gives the specifications for a VHF Marine Band radio to have a DSC Class-D rating. Please see:

Note that the specification does not require any particular NMEA-0183a serial data interface provisions on the radio. The interfacing of the radio to other devices via NMEA-0183a serial data communication links is a feature added by the manufacturers to facilitate linking to a data source for position information such as a GPS receiver, and to a position plotting display such as a digital chart plotter for display of received information

More information about DSC radio classifications can be found at

where2 posted 10-20-2007 11:46 PM ET (US)     Profile for where2  Send Email to where2     
Get a Standard Horizon PS2000 bundled with a Ram+ microphone for $150. Mount the radio Inside your console.

Find something else to fill the gaping hole with the extra $50. Maybe a little black cutting board from Wal-mart or the dollar store cut down to fit over the hole.

Post New Topic  Post Reply
Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.