APRS New User 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, PROTOPATH or
STATION
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 and network traffic is high.
DO use a WIDE over a RELAY if you
can work one directly.
DO make yourself a RELAY if you can
work a WIDE directly there and is no other stations within 40km of you
doing the same.
DO use the SSID of –1 if you have an
Alias set, be it Relay or Wide. Eg VK3DXD-1 has an alias of Relay set and
digipeats local traffic.
DO make sure RELAY stations are
separated by at least 40Km. This will stop duplicate packets from bouncing
around the network causing channel congestion. Remember that all Wide
Digipeaters are also RELAYs.
DO check your DIGI, PROTOPATH or
STATION
lists to see what stations you can work directly.
DO use actual callsigns in your Digi Path if appropriate, especially if you can see more than one RELAY but not a WIDE or you are running a fixed station. Example path: APRS via VK3ABC-1,VK3XYZ-1,WIDE
NOTE: Do not do this if the first station (VK3ABC-1 here) is a WIDE and Dumb APRS Digi! That is the same as WIDE,WIDE,WIDE! (see below)
DO use only enough hops to get your
packet to its destination, usually an IGATE (Internet Gateway). Example:
The IGATE VK3SB can hear the WIDE digi VK3RMD-1 Your path might be
RELAY,VK3RMD-1
DO set your minimum Automatic
Position Transmission Rate to the following:
Transmission Rates
DON'T use any of
the following paths:
DON'T put up a WIDE unless you truly
have wide coverage and there are no other WIDEs in your area, and unless
you plan to let it run 24 hours a day, 7 days a week.
DON'T use more than 3 hops. 3 hops will
give you coverage of approximately 250Km line of sight. Example path:
RELAY,WIDE,WIDE or VK3ABC-1,VK3XYZ-1,WIDE or RELAY,VK3ABC-1,WIDE.
DON’T set your station up as an IGATE
unless you can not reach an
operational IGATE on RF. This will only create traffic loops and problems
on the channel.
DON’T set your station up as a RELAY if
there is already a RELAY station close by. (See DO’s)
DON’T use excessive transmission power.
10 watts to 20 watts is more than enough.
DON’T set a mobile station up as a
RELAY or WIDE.
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! –