Connecting the Garmin GPS II+
Receiver to the Computer

First, put the batteries into the GPS unit, follow the instructions in the manual. The GPS unit should be located next to the computer, an external antenna outside with a clear view of the sky will be necessary. Unplug the small bar-shaped antenna, and attach the external antenna with the twist-on coaxial cable connector. Attach cable to the GPS unit, then connect the antenna to the other end of the extension. Coaxial cable lengths of 50 feet have been tested with no problems. (Do not exceed 80 feet)

The Garmin GPS unit is connected to the Macintosh Computer using an Apple serial "MiniDin8" cable (click to view wiring diagram). The Garmin Power/Data cable has loose wires at one end, and the connector at the other end that plugs into the GPS unit. The Macintosh serial "MiniDin8" cable must be plugged into the Modem serial port in the back of the computer. Wire colors of serial cable (in parenthesis on wiring diagram below) may vary among vendors. Wires should be checked.

Note: The newer Macintosh computers only support USB connections. In order to connect the receiver a "Serial to USB" adapter is required. The Stealth Serial Port is recommended for the Macintosh G3 and G4 computers. Information on the Stealth Serial Port can be found at http://www.GeeThree.com/.

Assuming that the cables are correctly connected together, the power supply runs the GPS unit (but will automatically switch to the batteries if AC power is interrupted), and the GPS unit is sending location & time information to the computer through the serial port. The only way to know for sure that the GPS unit is sending the proper information to the computer is by checking the Message Window of the GPSgraf program (covered in the software section). However, the screen of the GPS unit should be checked to see if the receiver is locked onto enough satellites to fix its location and absolute time.