What is a Digipeater ?In order to extend the range of transmission, APRS and UI-View use a facility known as digipeating ('digitally repeating') - this facility operates like a voice repeater albeit digitally. Any packet that is received by a station which contains either its own callsign, or an alternative callsign (known as an 'alias') within a part of the packet known as the 'Digipeater Path' is automatically retransmitted.
Each packet has the provision for up to seven digipeater callsigns within the 'Digipeater Path' and therefore can be repeated up to a maximum of seven times.
RELAY and WIDE ?APRS and UI-View make use of generic aliases of '
RELAY digipeaters are intended to increase the range of low-power mobile stations,
and should be closely spaced, therefore every station should enable the alias
WIDE digipeaters, as the name suggests, are intended to cover a large areas
and ideally are placed on high ground to provide maximum coverage - in a
similar manner to existing voice repeaters - typically 50 miles apart. The wide
area digipeater should have the generic alias '
For example a mobile station using a TH-D7 hand-held sends a message using with the following 'Digipeater Path':
Thus with only three packets, a message from a station using a hand-held transceiver is delivered to all the users within a 50 mile radius!
Duplicate RemovalThe range of transmission could be extended even further by amending the 'Digipeater Path' to '
Another possible cause of the ping-pong problem is an error in the firmware of some
TNCs. Instead of simply adding the '
Eliminating duplicate packets can prevent this problem. The system looks for packets with identical contents which occur within a predetermined time-frame and selectively ignore the packets that occur within it - however this must be short enough to allow for retries.
Callsign SubstitutionAnother means of resolving this problem is to replace the generic callsigns '
WIDEn-nAnother solution to the problem described above is WIDEn-n digipeating. A packet enters the network with the 'Digipeater Path' of '
The problem with this approach is that the path taken to get to the destination is lost,
the only way that a station can acknowledge message is to use '
TRACEn-nAs the name suggests, this feature allows the route to be traced. For example, a packet entering the network with the 'Digipeater Path' of '
The disadvantage of this method is that packets get progressively longer as they are repeated, making this less ideal for DX (The packet is longer, hence there is more chance of errors or collisions occurring during the time taken to transmit it).
UI-View reduces unwanted traffic, as acknowledgements are sent using UI-View by reversing the order of the received callsigns
Setting up a stand-alone Digipeater
Enabling DigipeaterThere may be instances when you may wish to allow your station to operate as a stand-alone '
Most TNCs provide the facility to operate as a simple digipeater. However, for this to work,
it must be enabled - to setup a TINY-2 use the following commands:
Now your TNC will digipeat any packet it hears with either your callsign, or the generic alias of '
Setting Beacon TextIn addition to providing a stand-alone digipeater, you may wish to also make the location of your digipeater available to other APRS users. The simplest method is to simply surround your locator square with square brackets, then add the remainder of your beacon text - this has the advantage that your beacon is also readable by human users on conventional packet!
The disadvantage of this type of beacon is that the location is only accurate to within one locator square and its format is incompatible with the Kenwood TH-D7 hand-held transceiver (showing as ??) on the display.
Alternatively, if you know your own latitude and longitude in Degrees, Minutes and Seconds from a map or a GPS Display. You can use a beacon text of the form:
You will first need to convert the seconds into decimal fractions of a minute. Simply dividing by 60 does this:
The GPS displays your latitude as
This format is compatible with all APRS systems
Enabling BeaconOnce you have defined your beacon text, you can then set your TNC using the following commands.
The position of your digipeater is now automatically transmitted once every 15 minutes to all users within range of the local '
It is not necessary to propagate this information any further than the local '