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post #11 of 45 Old 03-21-2009
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I don't get this spec: "Supports DSC (displays position data from DSC capable VHF radio)" -- shouldn't that be "to" not "from"? It is NMEA 0183-capable, and I would have thought the 620 could be connected to a DSC radio to supply the radio with position data.
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post #12 of 45 Old 03-21-2009
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The manual is online: http://www8.garmin.com/manuals/GPSMA...nersManual.pdf.

The 640 looks interesting, based on my quick read of that manual. Some comments/uncertainties:

1. Close to my personal sweet spot -- Can be used on our small sailboat for local summer coastal cruising augmented by laptop down below, and in the car or on vacations (portable). See also point 11.
2. Price point is up there - phew. Can get much larger screens from other manufacturers for less, but Garmin does make nice stuff. The price makes me think twice, though.
3. Can integrate XM satellite weather data.
4. Nice integration of AIS and other position data from a DSC radio, at least on paper, and presuming other people use their DSC radios.
5. Not clear to me how to network this device with a DSC radio and a wind meter, at a minimum. The 640 is NMEA 0183-capable, so is the idea to bus the 640 with other devices, presuming the 640 can supply the GPS sentences required by the other devices? Is NMEA 0183 enough these days, now that NMEA 2000 is out?
6. Screen is small, but I've been living with GPSMap 76C for years now, the 640 screen is twice the size, and that size of screen has found a big consumer automotive market, so it works for many.
7. Nice options for connecting to a computer for planning: SD card (though it is buried under the battery) and USB mini-port.
8. Short battery life compared to the 76C, so will need to ensure DC power is available.
9. I am not clear on whether the 640 can send position data to the DSC radio.
10. Garmin insists on calling intended tracks "course", and using "track" for "breadcrumb trail of past GPS fixes representing tracks made good", and using "heading" instead of "course being steered", but that's just my own pet peeve, shared by the tiny minority of consumer navigators, and I can work around it.
11. Speaking of consumers, this thing is a cool toy for the average recreational boater: decent marine navigation aid, but capable of good automotive navigation, displaying photo slide shows, and listening to XM audio by patching to exertnal speakers. They know their market.

On a serious long range cruise and bigger boat, I'd want a bigger screen and more chartplotting/networking capability, but I've got this product on my think-about list for our purposes.

Last edited by floatsome; 03-21-2009 at 05:52 AM.
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post #13 of 45 Old 03-21-2009
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A good full-feature DSC Class D VHF radio will have both NMEA 0183 in and out.

NMEA IN
—so that it can broadcast your position if you call for help.

NMEA OUT
—so that if someone else calls for help, it can plot them on your chart plotter... so you know where they are according to their DSC-broadcasted position.

Many of the low-end VHF units do not support this feature, but it is a good feature to have on your radio. For instance, if you call up a friend via their MMSI, you can see where they are in relation to where you are if they respond with a position update. If you're out fishing and want them to know where you're catching all the fish, but not have to announce it via voice....DSC is a good way to do it.


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I don't get this spec: "Supports DSC (displays position data from DSC capable VHF radio)" -- shouldn't that be "to" not "from"? It is NMEA 0183-capable, and I would have thought the 620 could be connected to a DSC radio to supply the radio with position data.

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post #14 of 45 Old 03-22-2009
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Quote:
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A good full-feature DSC Class D VHF radio will have both NMEA 0183 in and out.
I know that (taught the course for several years), but I did not see in the literature that the 640 is able to supply the radio with the host boat's position data in order to transmit the boat's position digitally, unless I missed something. It only talked about the 640 receiving position data from other boats via the radio receiver. Maybe that single NMEA link is two-way, and the literature simply did not specify it, or I missed it.
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post #15 of 45 Old 03-23-2009
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Floatsome—

If the VHF is DSC capable, it has to accept NMEA information in at a minimum, so that the DSC broadcast can send GPS based LAT/LON information during a distress call. The better DSC-capable radios, like the Icom M504 I use and unlike the Raymarine Ray54 VHF I used to use, can send GPS LAT/LON information to the chartplotter, so that an icon/waypoint for the sender's location appears when you receive it. Any GPS that is NMEA 0183 capable will provide the LAT/LON information to a DSC-capable VHF that is properly connected to it.

NMEA, being a serial protocol is a unidirectional protocol for each set of wires... there is always an NMEA data out and a separate NMEA data in. They never have both connections running over the same exact wire—they can't—RS-232/422 TX data lines can't receive data, and RS-232/422 RX data lines can't transmit data.

Some of the older chartplotters, which were designed before DSC-capable VHFs were common, can not accept the DSC-generated NMEA LAT/LON data and plot it on the screen. The software in them doesn't support that function. This is probably why the manual emphasizes this point—that it can supply the radio with LAT/LON position data is assumed.


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I know that (taught the course for several years), but I did not see in the literature that the 640 is able to supply the radio with the host boat's position data in order to transmit the boat's position digitally, unless I missed something. It only talked about the 640 receiving position data from other boats via the radio receiver. Maybe that single NMEA link is two-way, and the literature simply did not specify it, or I missed it.

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post #16 of 45 Old 03-23-2009
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Mystery partly resolved: the manual says nothing about how the 640 physically connects to an NMEA network, but this does: http://www8.garmin.com/manuals/GPSMA...structions.pdf. The 640 has both TX/RX connections, but they appear to be made through the marine-mount bracket. I can't tell if there is a connector in the 640 that mates with a connector in the bracket and the user wires the network into the bracket's cable, or if there are user-accessible NMEA ports on the 640 itself.
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post #17 of 45 Old 03-23-2009
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It looks like the bracket acts as a cable connection, so I doubt there's a separate NMEA 0183 interface on the unit.

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post #18 of 45 Old 03-23-2009
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Quote:
Originally Posted by sailingdog View Post
It looks like the bracket acts as a cable connection, so I doubt there's a separate NMEA 0183 interface on the unit.
Got one! There's a 24 "pin" connector on the bottom of the 640 that mates with the contacts on the mount. Having owned the 276c for many years now and enjoying the portability between car, bike and boat (incl charter boats), I have been waiting for this new gen 640. The user interface and the touch screen are taking some time to get used to. And it appears that if you want XM Radio or XM Weather, you have to connect the XM antenna via USB port (not the aforementioned 24 pin connector to the NMEA 0183 interface) so it does not seem to lend itself to a "permanent" xm install.

I have not yet obtained the g2Vision SD card so can't comment on that. It won't replace a full chartplotter onboard, IMHO, but seems like a good successor to the 276c line.

Oh and if you hunt around, you can find the units for around $980 as I recall.

Regards,
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post #19 of 45 Old 03-24-2009
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...it appears that if you want XM Radio or XM Weather, you have to connect the XM antenna via USB port (not the aforementioned 24 pin connector to the NMEA 0183 interface) so it does not seem to lend itself to a "permanent" xm install.
Very helpful - thanks. About the XM connection: would a little modification with a Dremmel tool give access to the USB port while the unit is mounted in the bracket?

I did that years ago with my old 76C bracket, and the modification has been working very well over the years (allows both power plug and USB connection while in the bracket). It exposes the wiring to weather risk, however, since of course the little black rubber plug has long since vanished.

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...won't replace a full chartplotter onboard...
I agree, but what is your rationale for this comment? It seems to me that larger consumer-grade chartplotters tend to be just bigger versions of the 76 and 276 families, without features that make it easy to modify waypoints and routes the way one can on a laptop using Mapsource or other PC nav programs. Professional chartplotters have many more features that make true electronic plotting and planning very easy, but that's still out of the league of most of us pleasureboaters, I suspect. And of course bigger consumer-grade chartplotters allow integrated radar/electronic chart display, which the 640 does not. (By "chartplotter" I mean a GPS display unit dedicated to the purpose, as opposed to a laptop/desktop configure for chartplotting).

Last edited by floatsome; 03-24-2009 at 06:26 AM.
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post #20 of 45 Old 03-24-2009
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Floatsome:

re: XM connection via USB, you won't need to pull out the Dremel to perform surgery on the mount. USB can be connected when the 640 is in the mount - it's just another connector dangling there, in addition to an XM radio audio out - wish they could've incorporarted this all into the multi-connector.

re: my comment about not replacing a full chart plotter, it doesn't overlay radar, it's not N2K - but as you point out, then we're in another price category.

But for it's purpose, I'm pretty happy with the 640 so far.

Regards,
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