If you have ever opened the live map at aprs.world and wondered how a low-power handheld in a remote valley ends up on a website seconds later, the answer is almost always a digipeater — a digital repeater that listens for packets on the local APRS frequency, decides whether they are allowed to be repeated, and rebroadcasts them on the same frequency so distant stations and iGates can hear them. Digipeaters are the connective tissue of APRS over the air, and how they are configured directly determines whether the network is efficient or saturated.
This guide explains what a digipeater is, what the cryptic strings like WIDE1-1,WIDE2-1 actually mean, why the network moved away from the old RELAY,WIDE,TRACE paths in the early 2000s, and what the difference is between a fill-in digi at the bottom of a hill and a wide-area digi on top of a mountain. It assumes you already know roughly what APRS is.
A digipeater is, in essence, a regular APRS station that is configured to retransmit packets on behalf of others. It hears a packet on the air, examines a special field called the digipeater path that the originating station included in its AX.25 header, and if the path still has unused hops left, the digipeater queues the packet, waits the channel-access interval, and transmits it again on the same frequency. Any other station — radio, iGate, or another digi — that is in range of the digipeater can now hear that packet, even if the original transmitter was out of range.
The mechanism dates back to standard AX.25 packet radio from the 1980s; APRS just imposes a community-agreed convention on top of it. There is no special hardware involved: most APRS digipeaters are ordinary computers (or a Raspberry Pi) running software such as Direwolf, aprx, YAAC, or Xastir connected to a transceiver and a sound interface. Some commercial radios with a built-in TNC — Kenwood's TM-D710G, Yaesu's FTM-400/500 — can also run as standalone digipeaters with no PC at all.
Every APRS packet carries a path in its AX.25 address field — a comma-separated list of callsigns or alias-tokens that describe how the originator wants the packet propagated. A typical mobile beacon looks something like this on the wire:
TA4OHN-9>APRS,WIDE1-1,WIDE2-1:!4030.00N/03253.00E>Mobile
The portion after APRS and before the colon — WIDE1-1,WIDE2-1 — is the path request. It is read left to right. The numeric suffix -N on each alias is a counter that gets decremented every time a digipeater consumes a hop. When the counter reaches zero, the alias is marked as "used" (the wire format flips a bit and prepends an asterisk in human-readable dumps) and no further digipeater will touch it.
Plain English version: WIDE1-1,WIDE2-1 says "I am willing to be repeated by one WIDE1-class digi (typically a low, local fill-in) and up to two WIDE2-class digis (typically wide-area mountaintop installations)." That is enough hops to get most mobile beacons across a metropolitan area without spamming the channel.
If you ever read old APRS documentation from the 1990s and early 2000s, you will see references to paths like RELAY,WIDE,TRACE2-2 or even RELAY,WIDE7-7. Those are the old paradigm, and they are no longer recommended anywhere in the world. They caused massive channel congestion because there was no good way to limit hops at the network level — a poorly configured tracker could (and did) flood entire countries with duplicate copies of the same beacon.
The fix is the New N Paradigm, drafted by Bob Bruninga and several network operators around 2004 and now the de-facto standard everywhere. The full text lives at aprs.org/newN/new-paradigm.txt. Three core ideas:
WIDE1-1 is meant for fill-in digipeaters — small, low-power installations at low elevations whose job is to grab packets from handhelds in valleys and re-emit them once so a nearby wide-area digi can hear them. WIDE2-N is meant for wide-area digipeaters — well-sited, mountaintop or tower installations that cover hundreds of square kilometres.WIDE1-1,WIDE2-1 (effectively two hops) and home stations at WIDE2-2 (two hops). Fixed iGates often beacon with no path at all (WIDE2-1 or empty) because they don't need to be re-broadcast — they are already on the Internet.The shorter the path, the better the network behaves. Old-timers will still say "use the minimum path that gets you heard"; the corollary is that paths longer than WIDE1-1,WIDE2-2 are a sign of bad configuration except in genuinely remote terrain.
The conceptual split between fill-in and wide-area digis is the cleanest way to think about the modern network.
Fill-in digis (sometimes called WIDE1-only digis) sit low — in a city neighbourhood, in a coastal town, in a campus building. Their RF horizon is small, maybe 10–20 km, but they are deliberately positioned where there is human density and where mobile stations would otherwise be invisible. A fill-in digi only repeats packets whose path requests WIDE1-1. It does not touch WIDE2-N packets — those are for the bigger sites. The classic use case: a handheld in a downtown urban canyon beacons with WIDE1-1,WIDE2-1. The local fill-in catches it and re-emits it with the WIDE1 slot consumed; a wide-area digi 80 km away on a mountain then catches the re-emission and propagates it further.
Wide-area digis sit high. A 600-metre tower, a mountaintop hut, a tall building rooftop. They listen for WIDE2-N traffic and re-emit it once, decrementing the counter. Because their RF horizon is enormous — often 150 km or more — they only need to fire once per packet to cover a whole region. A well-placed wide-area digi handles thousands of packets a day. Channel access has to be carefully managed: two wide-area digis whose footprints overlap will both hear an originating packet and both want to repeat it, which is why APRS digipeaters universally use a randomised wait timer (the famous "dwait" and "p-persist" parameters) before keying up.
A sensible regional network has one wide-area digi per major topographic feature and a sprinkling of fill-in digis around population centres. Build it the other way (lots of wide-areas, no fill-ins) and you saturate the channel while still failing to hear urban handhelds.
The New N Paradigm also defines a few aliases that are not generic WIDE hops:
SAR — Search and Rescue. Used during incident responses to mark traffic that should be prioritised. Not all networks honour it; check with your local emergency-comms coordinator.TEMP1-1, TEMP2-1 — temporary deployment aliases for portable digis at events. Configured exactly like WIDE but kept distinct so they don't clash with permanent infrastructure.ECHO — a single-hop alias used for connectivity testing. Beacon with path ECHO and only your local digi should repeat you back; useful for confirming you can hit the local site.GATE, NOGATE) for traffic that should or should not cross specific gateway points.Most operators never need to touch anything beyond WIDE1-1,WIDE2-1 for mobiles and WIDE2-2 for fixed home stations.
Open any decoded packet in a tool like aprs.fi, aprs.world, or a console listener and look at the path field. Each digipeater that touched the packet appends its callsign with a trailing asterisk to indicate the packet went through it. So a packet that originated as:
TA4OHN-9>APRS,WIDE1-1,WIDE2-1
might arrive at the iGate looking like:
TA4OHN-9>APRS,TA1FILL-1*,TA1WIDE-3*,WIDE2*
That trace says: it was repeated first by TA1FILL-1 (the local fill-in digi, which consumed the WIDE1-1 slot), then by TA1WIDE-3 (a wide-area site, which consumed the first WIDE2-1 hop), and then was picked up by an iGate. Reading the trace backwards is the fastest way to figure out which digi is hearing you and which is not.
If you want to add capacity to your local network, the recipe is straightforward:
DIGIPEAT 0 0 ^WIDE1-1$ ^ ) or a wide-area (DIGIPEAT 0 0 ^WIDE[12]-[1-7]$ ^).Run it 24/7, with battery backup, and you become part of the public infrastructure of APRS in your area. Few hobbies offer that for the cost of a Pi and a clean antenna feed.
A digipeater's job ends at the airwaves; getting packets to the global network is the job of the iGate. Many sites combine the two roles on the same Pi — Direwolf and aprx will happily do both simultaneously. The separation of concerns matters though: a pure digi without an iGate still adds value to the local RF network, and a pure iGate without a digi still adds value to the global Internet feed. Read more in the companion iGate setup guide, and learn how the Internet backbone works in the APRS-IS network explainer.
The digipeater network is what makes APRS feel magical from the operator's side: press one button, appear on a map across the country. Understanding how it works is the difference between using it and trusting it.