Updated: 20/10/2004

APRS Users Guide

This document has been written to familiarise you with the concepts of APRS operations so that you can get running with maximum efficiency and minimum disruption to other stations in the network. This document has been written generically to apply to all versions of APRS, for information on how to alter the settings that will be discussed herein, refer to the docs for your version of APRS/MacAPRS/WinAPRS/UI-View.

 Since APRS stations do not "connect" to each other as in a typical packet QSO, but rely on "unconnected" packets, the only way to get your data to others beyond your station's reach is through the use of digipeaters. Users of APRS have standardised on a scheme for digipeating that requires some explanation.

 Just as it is advantageous to have a packet node or a repeater located in a high spot with great coverage, so it is with digipeaters. In APRS terminology, such a wide-coverage digi is called a WIDE. In any given area, there should only be one WIDE, and that station should be able to work the adjacent WIDEs and should operate 24 hours a day. Don't be an "ego-WIDE"; that is, setting yourself up as a WIDE when you cannot provide the functionality of a true wide or are in an area already served by a proper WIDE. You will only cause problems on the network and earn the wrath of those whose traffic you are affecting.

 Of course, we cannot expect every station in a given area (mobiles especially) to be able to work a WIDE (especially if they are on the move), so to assist those stations to make a WIDE, there are RELAY stations. A RELAY station can be any station that can work one or more WIDEs reliably. There should be only one RELAY in a given area that can work a given WIDE; the same "ego-WIDE" caution applies here. Of course, if two (or more) stations overlap in coverage slightly but primarily cover differing areas, the benefits of covering the extra area might outweigh the extra traffic and collisions on frequency. This is where those Ham "experimenter" skills come into play. Remember, when all is said and done, we're here to innovate and experiment while (hopefully) having fun. Don't get too obsessive or relaxed with any of the guidelines herein.

 So now, as a user, needing to choose a path to digi your packets through, what should you use? Initially, set your UNPROTO path to RELAY (see your program docs for info on how to do this). Once you see some stations appear on your map, see who you can hear directly using the DIGI or PROTOPATH list. Can you hear a WIDE directly? If so, change your UNPROTO path to WIDE (or WIDE,WIDE if you want to go two hops). If not, and you can work a RELAY directly; try RELAY,WIDE (or RELAY,WIDE,WIDE).

 APRS Digipeaters are normally APRS Network Smart, which means they understand what RELAY and WIDE mean and they do not digipeat a packet more than once (using callsign substitution). Some digipeaters such as NetRom nodes are Dumb APRS Digis and will digipeat a packet they have previously digipeated if they hear the packet retransmitted (digipeated) from another APRS Digi. For example, using an APRS network smart Digi the path of WIDE,WIDE,WIDE will be passed as DIGI1,DIGI2,DIGI3. Using a dumb APRS Digi network the same path would end up with duplication as DIGI1,DIGI2,DIGI1.

 You may also see a GATE,  IGATE or SGATE station. GATEs pass traffic from HF nets to VHF nets, IGATEs pass traffic from VHF to the Internet and SGATEs pass traffic from Satellites to VHF. GATEs should never be used from VHF to HF - this will have reeeal bad implications for the HF net (perhaps even crippling the entire net). The 300 baud traffic of HF should pose no problem on the VHF 1200 baud net, but the reverse is certainly not true. The same rule applies for IGATEs and SGATEs, they should never be used to pass traffic from the Internet to VHF (Except for designated stations under very controlled conditions).

 When mobile there is always tendency to use as higher power as possible to make sure you get through. This is not normally true for APRS. It is better to use power levels of between 10 watts to 20 watts maximum. This will give you full coverage into the digipeaters while at the same time limiting excessive duplication of network traffic. Mobiles should also set their transmission times to 2 minutes or greater, especially in the city where vehicle speeds are low.

DIGI PATH DO'S AND DON'TS:

DON'T use any of the following paths:

DON'T take all of these as gospel. Circumstances vary from location to location and you may need to bend or break these rules-of-thumb in your area. But DO check with your APRS neighbours first! –