[aprssig] advice on purchesing GPS for use with D-710

Tom Russo russo at bogodyn.org
Sun Aug 28 15:52:06 CDT 2011

On Sun, Aug 28, 2011 at 04:28:09PM -0400, we recorded a bogon-computron collision of the <wa8lmf2 at aol.com> flavor, containing:
> On 8/28/2011 3:46 PM, J T wrote:
> > Or the new Garmin Montana series.  The Montana 650t comes preloaded with topo 
> > maps although you can load other maps into them, too.  It has a large 
> > touch-screen display (very nuvi-like), a serial port for direct connection to 
> > a D710, and can also be used as a portable GPS.
> >
> > -Jerome, W0JRT
> >
>  From what I can determine from Garmin's own description/specs, it appears to 
> only have a USB interface.
> There is no mention of a classic RS-232 serial port (required to connect to a 
> Kenwood), nor any mention of FMI support (that allows the USB interface to 
> "morph" into a serial port when a special cable is attached).

FMI and "morph to serial" are separate things.

Several of the handheld usb-only Garmin GPS units will indeed "morph to serial 
NMEA" with just the right cable, even though they don't talk FMI.  If you look 
at the Montana's spec  says its interface is "USB and NEMA 0183 compatible," 
and on its "accessories" page there is a USB "Serial Data/Power" cable
with bare wires to access the serial data.  This cable is compatible with
several of the devices other than the Montana, including the Colorado, Oregon, 
and GPSMAP 62 series. 

I believe that the way these devices work (Scott Miller can correct me here 
if I'm mistaken) is that they detect a certain resistance in the cable between 
certain pins, and switch from USB to plain RS232 serial protocol on the data 

FMI, on the other hand, is a specific fleet management protocol that enables
appropriately written software to control (and be controlled)  by the GPS,
and it is usually present only in devices intended for vehicle use.  The
Montana is targeted for handheld use, particularly for hiking.  It is not,
as I understand it, specific to whether the actual communication is done
over RS232 or USB.  I believe the FMI cables generaly *do* also kick the
device into serial mode, though.  Again, Scott Miller can pipe in and
correct me if I've misunderstood him or the various FMI specs I've read.

Tom Russo    KM5VY   SAR502   DM64ux          http://www.swcp.com/~russo/
Tijeras, NM  QRPL#1592 K2#398  SOC#236        http://kevan.org/brain.cgi?DDTNM
 "One man alone can be pretty dumb sometimes, but for real bona fide
 stupidity, there ain't nothin' can beat teamwork." - Edward Abbey

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