Note that you DO NOT have to purchase one of the brand-spanking new APRS/GPS capable TNC's in order to participate in APRS activities. Many older TNC's can be used, including the AEA PK-88, TAPR-2, TAPR-2 clones made by various manufacturers, etc. These units can be put to use as home stations or as mobile APRS stations. For a home station the position is set in the beacon text and is broadcast at 10 minute intervals. For mobile APRS these TNC's must have a computer attached and running APRS software in order to update the position. The older TNC's are not usable as WIDE digipeaters, and are ill-suited as mobile/portable trackers unless some form of computer is attached constantly.
TAPR-2 clones can be upgraded with new EPROM's to make them GPS-aware. There are certain caveats with this, because the processor inside the TAPR-2 TNC's is slow and may not handle continuous sentences from a GPS. If your GPS has enable/disable for individual sentences then you may want to turn off all strings, and then re-enable just the $GPRMC or the $GPGGA string so the TNC can keep up with the data. See the TAPR Site for information about updated EPROMS. These updated EPROM's are only necessary if you wished to run a mobile APRS setup with no computer attached.
When using an older TNC for your house and RELAY station, insert your position fix in the BTEXT, set the TNC to beacon at 30 minute intervals, and set up an alias of "RELAY". Here is an example:
mon off mycall pa3xyz myalias relay unproto aprs via wide btext !5148.16N/00543.68E#PHG6060/ Wijchen JO21UT (http://aprs.gids.nl) beacon every 250 (might need to be 600 depending on TNC) txdelay 25 digipeat off xmitok on ctext Sorry its not monitored here.. Only APRS freq you will be disconnected. cmsg on cmsgdi on max 1 dayus off dayt yymmddhhmm mst on
TNC's are now available that have two serial ports and a radio port. One serial port can connect to a computer, while the other connects to a GPS. If you already own TNC's that only have one serial port, don't despair, there is a way to hook up a GPS and the TNC to the computer at the same time: It's called an HSP (hardware serial port) adapter. You can either build or buy an HSP adapter, and it generally consists of a Y-adapter cable with a small circuit inside. The circuit switches between the TNC and the GPS based on a handshake line coming out of the computer. This handshake line is in turn controlled by the APRS software running on the computer. You merely have to inform the APRS program that you're using an HSP adapter. See the main NWAPRS web page for a pointer to the circuit, or visit the TNC manufacturer's web pages to see what they offer.