Digipeaters and iGates
| Digipeaters and iGates | |
|---|---|
| Network | APRS and other packet radio |
| Digipeater | Digital repeater that resends a packet on the same frequency |
| iGate | Internet gateway between the radio network and APRS-IS |
| North American frequency | 144.390 MHz |
| Paths | |
| Usual mobile path | WIDE1-1,WIDE2-1 |
| Fill-in alias | WIDE1-1 |
| Path system | WIDEn-N ("New-N paradigm", 2004) |
| Software | Dire Wolf, aprx |
| Building one | |
| Stand-alone hardware | Dedicated controllers such as the Microsat WX3in1 |
| Common SSID for iGates | -10 |
Digipeaters and iGates are the two kinds of relay station that let APRS packets travel beyond the range of a single radio. A digipeater (digital repeater) hears a packet on the air and sends it out again on the same frequency, usually from a hilltop or tall building, so that a low-power mobile or handheld station is heard across a whole region. An iGate (internet gateway) passes packets heard on the air to the APRS Internet Service, or APRS-IS, a worldwide network of servers whose data appears on public maps such as aprs.fi. Many stations do both jobs at once.
Digipeaters
A voice repeater receives on one frequency and transmits on another at the same moment. A digipeater works differently: it receives a whole packet, stores it, and then retransmits it on the same channel once the channel is clear. This approach, called store and forward, needs only one frequency and a single ordinary radio, with no duplexer.
Before relaying, a digipeater checks the packet's path, a short list of instructions written into each packet by the sending station. If the path asks for a relay the digipeater is set up to provide, it resends the packet and marks that step as used. Digipeaters also remember packets they have recently sent and ignore duplicates, so the same report doesn't bounce around the network.
Two broad kinds are used on APRS:
- Wide-area digipeaters sit at high sites and cover large areas, often relaying packets more than one hop.
- Fill-in digipeaters are low-level stations, often at a home, that cover a gap such as a valley or a stretch of highway that the wide-area digipeaters can't hear. They relay only the first hop of a packet.
Paths and WIDEn-N
Every relay of a packet occupies the shared channel for everyone, so the path limits how far each packet spreads. Since the New-N paradigm introduced in 2004, APRS in North America uses the generic alias WIDEn-N, where n is the number of hops requested and N counts how many remain. Each digipeater that relays the packet reduces N by one, and when N reaches zero the relaying stops.
| Path | Typical use |
|---|---|
| WIDE1-1,WIDE2-1 | Mobiles and portable stations. The first hop can be taken by a fill-in or a wide-area digipeater, the second only by a wide-area one. |
| WIDE2-1 or WIDE2-2 | Fixed home stations. They should not request WIDE1-1, which is meant for weak mobiles; where coverage is good, one hop or no path at all is often enough |
| WIDE3-3 | Only in sparsely populated rural areas where digipeaters are far apart |
Older aliases such as RELAY, TRACE and a plain WIDE are obsolete, because they produced duplicate copies of each packet. Asking for more than two hops is discouraged except in thinly populated rural areas, and digipeaters in busy regions are often set to ignore requests for long paths.
iGates and APRS-IS
An iGate connects a receiver to the internet. Every packet it decodes is sent to APRS-IS, which shares it with all connected servers, maps and programs. This is how a station in a remote valley can appear on a map anywhere in the world, and why a packet does not need to reach a distant digipeater to be seen online. Uploading requires a passcode linked to the operator's call sign.
A receive-only iGate just listens and uploads, and can be built from a computer and a cheap software-defined radio dongle. A two-way iGate also transmits, sending messages addressed to nearby stations from the internet back out on the air. Because that is a radio transmission, it follows Part 97 like any other, and well-run iGates send only traffic for stations known to be local. By convention, iGates often use the SSID -10 after the call sign.
The map site aprs.fi collects APRS-IS data and shows each station's position and raw packets, including which digipeaters and iGates handled them.
Building one
Most digipeaters and iGates use an ordinary FM mobile radio on a well-placed antenna, plus something to decode and send packets:
- Software modems. Dire Wolf, by John Langner, WB2OSZ, runs on a computer or Raspberry Pi with a sound adapter and can act as a digipeater, an iGate, or both. aprx, by Matti Aarnio, OH2MQK, is a Linux program that began as a receive-only iGate and later gained multi-port digipeating, including settings meant for fill-in stations.
- Stand-alone controllers. Boxes such as the WX3in1 Plus 2.0 from Microsat in Poland combine digipeater and iGate functions with inputs for a weather station.
- Radio and filtering. A permanent station transmits often, so a commercial-grade radio that tolerates a high duty cycle is a good choice. At busy sites a cavity bandpass filter tuned to the APRS frequency keeps out strong nearby transmitters, and lightning protection is essential, as described in Grounding and lightning protection.
The International Space Station also carries an APRS digipeater, on 145.825 MHz or 437.825 MHz depending on which radio is active (437.825 MHz as of October 2026), which portable stations use to relay position reports across hundreds of miles. ARISS posts which radios are running on its status page.