It has one, it’s just well hidden!

The GPSMap 62s can be paired with an appropriate amateur radio for full APRS functionality.

Some brief history before I begin…

Most modern GPS devices have dropped their old fashioned RS-232 serial ports in favor of the much more user friendly USB port. This makes interfacing them to amateur radio projects much harder, bordering on impossible. While standard serial ports could be thought of as a peer to peer system, USB was designed to work as a client server model with the “server” requiring much more intelligence than we generally have available in our projects. To make matters worse, despite it’s name “Universal Serial Bus” the creators didn’t impose any universal “driver” for serial communications the way they did with mice, keyboards, audio devices, etc. These factors all combine to make USB very unfriendly for us hams.

The older Garmin 60-series was a great product for amateur radio because in addition to the “new” USB it still supported the standard Garmin 4-pin serial/power connector. When I made the decision to sell my 60’s and upgrade to a 62 I knew I was giving up APRS connectivity but since I used it so seldom it was a trade off I was willing to make.

It turns out that Garmin has retained RS-232 connectivity in some of their newer GPS devices, they’ve just made it a bit harder to access. Using the Garmin Serial Data/Power Cable you can wire many, but not all, Garmin USB-only GPS devices into applications that require RS-232 level NEMA compatible GPSs. This cable enables the GPS to support bidirectional RS-232 level NEMA sentences at 4800 baud. This is exactly what is needed for compatibility with APRS as well as most anything else that wants GPS data. If your radio has the capability to send received APRS stations to the GPS as NEMA waypoints they will appear on your map in realtime just like the older 60 series.

There is one drawback though: the cable requires power, and not a small amount of it. When connected to this cable, the 62s will not use it’s internal battery at all, it relies on power fed to it via the cable. The cable has a built in voltage regulator and will accept anything from 8 to 36VDC, and at 13.8 it was drawing between 100 and 200mA with my 62s powered on and attempting to get a fix. On the plus side, you don’t need AA batteries in the GPS when using the cable so I suppose it’s just moving a battery from point A to point B, but still not as convenient as it could be for portable operations.

I’ve tested this with a Kenwood TM-D700, and a TH-D7A and of course a serial port on a PC. It should also work with the TM-D710A, TH-D72A as well as the Yaesu VX-8GR (at least for display on the later two as they have their own built in GPS engines).

I said above it works with some but not all Garmin GPS units. Garmin lists some compatible devices in the Oregon, Colorado and Zumo lines on their website but I don’t think that’s an exhaustive list. Garmin lists the 62st as compatible, but not the 62s that I tested (identical hardware, the st just includes more maps). I’m fairly certain it would also work on the GPSMap 78 series, as it shares nearly identical hardware and identical firmware with the 62 and there are probably others that will work as well. I can say for certain it does not work with my Nuvi 765T, v4.0. I’m looking for people locally with newer Nuvis to see if perhaps it will work with some of the newer units.

Short of purchasing a cable and trying it, the only way I can advise for you to tell if your GPS might work will be to check it’s system settings. The 62 has option for “Interface” that can be set to NEMA In/Out, Garmin Serial, Garmin Spanner, Text Out or RTCM. I always thought that option odd since it had no interface, but I think it’s a good bet if you can find an option like that your GPS will work with the cable.