N2QDK-9

Background

My RAV4 contains APRS (Automatic Packet Reporting System) hardware. APRS uses Amateur Radio to transmit real-time position reports, weather reports, and messages between users via RF (radio frequency). In my case, it transmits a beacon with my vehicle's location, obtained via GPS, every 15 minutes; more frequently if the vehicle is in motion. Think of it as a poor-man's lojack.

However, with the addition of the Garmin Nuvi 350 as GPS and display, I can see other APRS stations as a waypoint plot on Nuvi's on-screen map, as well as send and receive messages to other people via the radio.

All data on the local RF is ingested into the APRS Internet System (APRS-IS) and distributed globally for instant access via the Internet.

To the right is the view of the Argent Data Systems OT2m TNC and the radio, a Yaesu FT-2800m, all hidden in a rear cargo compartment of my RAV4. All cables are run inside body pannels, under floorboards, or otherwise hidden.

Bob WB4APR is now pushing the two-way messaging aspect of APRS, with web/Internet connectivty. An APRS tracker/mapping program for the iPhone is in developement and is expected to be released before the holidays. Fun things are ahead for the world of APRS, as consumer electronics are brought under our umbrella and everyday usability increases.

Below is the last known position of my vehicle according to APRS-IS:

Hardware

• Radio: Yaesu FT-2800m, usually transmitting at 25 watts, but I'll kick it up to 65 watts when traveling in the Adirondacks or anywhere else where coverage is spotty
• Antenna: Generic through-the-glass quarter wave vertical
• TNC/Tracker: Argent Data Systems Tracker2 OT2m, configured to digipeat TEMPn for temporary and special event use
  
• Interface Cable: Garmin FMI (Fleet Management Interface) Serial-to-mini USB cable
• GPS & Display: Garmin Nüvi 350

Setup & Configuration

It has taken me about two years of fiddling with different equipment to get to this point. Nice and simple, with the absolute minimum wires. For TNC's, I have tried a TinyTrak3Plus (non-upgradable firmware and terrible RF isolation), OpenTracker+ (a fantastic tracker, but I wanted something that could operate as a digipeater if needed). In January 2008, when Scott N1VG announced that his OT2m TNC can talk to the Garmin Nuvi 350 to recieve GPS data, and plot local RF objects as waypoint on the Nuvi's map display, I knew I needed to get my hand on at least one OT2m ASAP.

Above is a closeup of the cargo compartment, which is usually covered by a removable pannel. The large black thing that looks like a huge heatsink is the Yaesu FT-2800m radio. The smaller black box conspicously labeled is the Argent Data Systesm Tracker2 OT2m TNC. The top silver connector out of the back of the OT2m is a DB9 plug that goes to the Garmin Nuvi 350 GPS that sits on the dash. The bottom DB9 is for power and radio transmit and receive audio (the white and black cables, respectively).

What you can't see is the 10 gauge wire that's connected to the positive battery wiring harness, runs through the firewall, and runs to the back cargo area. The 2003 RAV4 does offer a switched cigarette lighter jack just below the cargo compartment. When the ignition is off, power is cut. This isn't useful for me as I wanted an always-on solution, with the obvious caveat that if I don't drive my vehicle within three or four days, I may come back to a dead battery. Eventually I'll put a toggle switch in to allow easy switching between always-on power and ignition switched power.

Also not shown: The power cords terminate to a 15 amp PowerPole interconnect, where a short jumper containing two 15 amp inline fuses and interconnect to the blade harness used by the FT-2800m. It is important to remember safety, and the first rule is to fuse-protect everything.

The OT2m takes two DB9 connectors, one for audio in/out and power, the other for the GPS/data. Connecting the OT2m to the radio required two wires, one 1/8" male mono (black) wire that goes into the speaker jack of the radio, the other (white) wire goes to the 6 pin RJ11 modular mic jack. The Yaesu FT-2800 comes with a backlit handheld microphone, which is enough juice to power the OT2m! Here is the pin configuration.

My OT2m reports it as 7.7 volts, which appears to be very well regulated by the FT-2800m radio. It doesn't matter if the vehicle power into the radio is 12 or 14 volts, it is consistatly 7.7 volts out of the mic jack. I'm not sure how much current the FT-2800m radio can provide, but the OT2m is rated to draw a max of 30mA during transmit (which lasts less than two seconds), otherwise 12mA when idle, which hasn't been a problem. The OT2m is happy with anywhere from 6.5 - 28 volts.

The other DB9 connector goes to the Garmin FMI (fleet management interface) cable, which plugs into the Nuvi 350 as a mini-USB connector. The OT2m is in the rear of the vehicle and the Nuvi sits on my dash; A 15 foot cable run was needed. Due to the availability of a few hundred feet of Cat5e ethernet cable sitting on a shelf, I just used that. It's worked well for six months without any issues.

It is a completely out-of-sight install when the cover of the storage area is in place.

To have the OT2m talk to the Nuvi 350, the Nuvi must receive external power (not run off of its internal battery). This means plugging the mini USB power connector into the Nuvi mount, and putting the Nuvi into the mount. Then plug the FMI cable into the side mini USB plug. When plugging the FMI cable into the Nuvi 350 for the first time, the FMI mode is enabled, which changes a few of the menus. It takes a little getting used to, but isn't bad at all, considering the additional functionality you'll gain, such as sending and receiving text messages.

I still need to add the configuration setting I have running on the Tracker2 OT2m.

Using the Garmin Nüvi 350 for APRS

The map display is the most basic element for any on-dash GPS navigation system. The Garmin Nuvi 350's integration with APRS includes the placement of local objects heard via RF plotted on the map as a waypoint.

The screenshot to the left shows a number of APRS objects plotted as waypoints in Central New York.

Not only can objects be plotted on the map, they can be listed in table form with distance and a direction indicator, based on your current direction of travel. This is accessed by going into the "Favorites" menu. To the Nuvi, APRS objects are stored as a Favorite.

If you click on an object/waypoint, it will show you the CALLSIGN-SSID and the APRS comment for the station. This is especially useful for voice repeater objects and meeting notices, see below. If you click on "Show Map," the Nuvi will display the object/waypoint and the surroundings.

If you click on the "Go" icon, the Nuvi will route you to that location! This is really useful for hamfests and club meetings.

The bottom two objects have a blue background because the screenshot was captured while the Nuvi was in nighttime mode.

Two-way Text Messaging

Where the Nuvi/OT2m combo really shines is in its text messaging abilities. When an APRS message is sent to you, an exclamation point icon will show up on the screen, and it will make a "bong" alert sound.

Clicking on the exclamation point will take you to the incoming messages screen. Clickon the message to show the entire message. The Nuvi keeps track of read and unread messages by way of a different envelope icon.

One downside of Nuvi/OT2m messaging is that if the Nuvi is powered down, it will not receive any messages, even if the OT2m remains powered on. When my vehicle is off, the radio and OT2m remain powered (and will act as a TEMPn digipeater if needed).

To the right is an example message sent via Steve's FindU.com website, now that message sending capabilities have been added. I sent this message using the Safari browser on my iPhone.

From the time I clicked the send button on the website to send the message to when I recieved a notification on the Nuvi was under 5 seconds! This is absolutely amazing, and certainly much faster than I was expecting.

Sending a message from the Nuvi is just as simple. The format is -CALLSIGN MESSAGE.

Expanded APRS messaging interoperability between the RF and Internet (including cellphone SMS texting) will only further usability. I would rather receive short text messages, weather or other alerts for my local area via APRS RF and have them displayed on my dash on the Nuvi than via my iPhone while driving.