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7 APRS NETWORKS
34 CONTENTS TM-D710A/E
7.4 Digipeaters (Digital Repeaters)
The greatest feature of APRS is the network that is spreading around the world. The heart of the
network is made up of many digital repeaters commonly referred to as digipeaters. Of course,
digipeaters are well-known among those who have used packet radio for years. Digipeaters
receive data over-the-air via radio signal and repeat or relay it onward. For a voice repeater, two
different frequencies are used simultaneously to accomplish this repeater function. However, a
digipeater first receives and stores data, and then transmits when the channel clears.
In the earlier times of packet radio and digipeaters, it was required to specify the callsign of each
digipeater station. But it was difficult to know which digipeater station to use. If moving in a
vehicle, you had to constantly consider changing digipeaters. Now, APRS uses a common
generic callsign for all digipeaters referred to as WIDEn-N, where N is the number of hops desired
through the network (typically 2). The WIDE terminology lets you know the digipeater is in a good
location for repeating signals. A mobile station anywhere only has to specify WIDE1-1 without
needing to know a specific callsign of a digipeater in order to digipeat their beacon transmission.
APRS evolved over many years beginning in 1992, and there were many inefficient older network
concepts that were still being used in some areas. You still may see references to these obsolete
techniques (RELAY, WIDE, TRACE, and TRACEn-N). By 2004, it was decided it was time to
abandon those many older inefficient paths and concentrate on only the fully traceable WIDEn-N
algorithm. This universal upgrade of the APRS network to just the one simple and traceable
WIDEn-N concept was called the New-N Paradigm. Since its adoption, most areas have seen
many improvements in local area APRS reliability. In most areas of the country, the number of
hops should be no more than WIDE2-2 because additional hops just add too much network load
and too much interference from stations far away.
The following sections explain configuration of the TM-D710A/E for use with digipeaters.
7.4.1 UIDIGI
With UIDIGI activated (On), when a digipeater receives a UI frame with a character string for alias
(such as RELAY, WIDE1-1, etc.) that matches the alias character string in the digipeater, the
digipeater repeats the packet substituting the callsign from the digipeater’s MY CALLSIGN
configuration and adding a completed flag (*).
UIDIGI should normally be off in a mobile. It is not good for mobiles to be digipeating all packets
on the channel because it causes much interference. But sometimes, in special cases, when a
mobile is being used on top of a hill or a special weak area to provide temporary emergency
digipeating, then UIDIGI can be enabled with the WIDE1-1 alias so that this mobile can serve as
the first hop out of an area. WIDE1-1 digipeating only operates on the first hop, so there is not
much damage to the network or to other traffic
Figure 7-5 Using UIDIGI
MYCALL: N6NRR
UIDIGI: ON
ALIASES: WIDE1-1
WB4APR-9 > APK102,
WIDE1-1, WIDE2-1: Test
WB4APR-9 > APK102,
N6NRR*, WIDE2-1: Test