At the June 5th, 2003 General meeting of the Anoka County Radio Club, board member Tim Neu (KC0LQL) was selling a kit with a GPS receiver, Active GPS antenna and the antenna interface cable to the GPS receiver. These new units where left over from a canceled project and Tim jumped on them at a great prince. This handy GPS receiver module could be used as part of a APRS system. This page cover just some of the details on the units sold along with schematics and design ideas on how to interface a module to items like a Palm Pilot, laptop computer, TinyTrak3 GPS position encoder (APRS) and more.

Before we do anything we need to know as much as possible about the G8 GPS module as we can get. As it turns out, just about everything known about the modules itself could be found at manufacture's, Thales Navigation (aka Ashtech), website under the product name G8 GPS receiver. Here is a 2.7M zipped file containing all the documentation for the G8 GPS .

The other key item of the GPS kit is the GPS active antenna is made by Matsushita Electric Works. Known as the NAiS GPS Antenna model CCAF20KG01, a data sheets and/or specs where not as easy to locate. But if you can read German, we did find a copy at the manufacture's German web site at http://www.matsushita.de. These units are known as the VIC1-LP on this web site. The key peace of data is the 5Vdc at 50mA max operational voltage and current for the active antenna. We now know the supply voltage to put on the GPS receiver's antenna power pin (pin2).

One possible interface match would be to using these GPS units with the Byonics TinyTrak3 encoder. This neat little unit provided a low cost interface between a GPS device and a radio. The TinyTrak3 takes case of all the control and encoding operations.

Here is the first round working schematic by Dave Runkle (KC0KEP) that he has been successfully testing on his APRS laptop and TinyTrak3.

(Click on the image for FULL size)

While the above design does a good job, an integrated solution which would incorporate both the TinyTrak3 and the GPS electronics on to one printed circuit board would be a nice addition. Again Dave Runkle (KC0KEP) designed just such a board. Follow the TinyTrak3 Plus GPS link to see a PDF file with the current schematic, board layout and parts list.

This board reproduces the TinyTrak3 electronics plus adds support for the G8 GPS module. With this board there is two modes of operation.

In normal run mode (U3 pin 1 floating high), all sent and received serial data is routed to the G8 module. In addition, the out going serial data is also presented to the serial input on the TinyTrak3 processor (U1 pin 3). This allows both an external GPS device and the TInyTrak3 to work at the same time in most all normal modes of operation. The external serial device has full control over the operation the G8 GPS module. But you must remember make sure to have the two minimum $PASH sentences enabled on the G8 GPS module for the TinyTrak3 to work. The TinyTrak3 needs them to calculate and report it's position.

In program mode (U3 pin 1 pulled low), all the received and sent serial data is routed only to the TinyTrak3 chip. The G8 GPS module is not connected to anything in this mode. This allows you to program the TinyTrak3 with the normal Byonics software.

At present three prototype board using the new design are in use. Two by Dave Runkle (KC0KEP) and one by Dave Holter (KC0HJA).