TARPN
| TARPN | |
|---|---|
| Full name | Terrestrial Amateur Radio Packet Network |
| Type | A design for building packet radio networks |
| Website started | 2014, by Tadd Torborg, KA2DEW |
| Home area | Raleigh, Durham and Chapel Hill, North Carolina |
| Technical | |
| Links | Dedicated point-to-point radio links, one frequency per pair of nodes |
| Node computer | Raspberry Pi |
| Node software | G8BPQ's LinBPQ |
| TNCs | KISS TNCs such as the NinoTNC, TNC-Pi and KPC-3 |
| Operating | |
| Radios | VHF and UHF FM radios, often used mobiles or surplus commercial units |
| Internet use | None; the network is built to run without it |
TARPN, the Terrestrial Amateur Radio Packet Network, is a way of building packet radio networks from dedicated point-to-point radio links between home stations, using Raspberry Pi computers, simple TNCs and inexpensive FM radios. It is centered on the Raleigh, Durham and Chapel Hill area of North Carolina, and its website, started in 2014, is maintained by Tadd Torborg, KA2DEW. TARPN describes itself not as a club but as a set of methods, kits and guides that any group can use to build its own network. The project reported about 560 participating hams in May 2023.
Design ideas
Classic packet networks put many stations on one shared frequency. Every station must wait its turn, and stations that cannot hear each other transmit on top of one another, a problem known as the hidden transmitter. As traffic grows, collisions and retries can bring a busy channel nearly to a halt.
TARPN avoids this by giving every link its own channel. Each pair of neighboring nodes is joined by its own pair of radios on a frequency used only by that link, much like a cable run between two buildings. Because only two stations ever share a channel, collisions are rare and each link can run at its full speed. A node with three neighbors therefore has three radios, three TNCs and three antennas, all connected to one computer, and messages hop from node to node across the network.
The project's stated goals are the lowest cost for the performance, equipment that as many hams as possible can build themselves, an interesting operating experience, and room for participants to experiment and improve things. It also aims to draw in new and younger hams. The network deliberately does not use the internet; TARPN values a network that stands entirely on its own radio links.
Building a node
A TARPN node is built around a Raspberry Pi running LinBPQ, the node software by John Wiseman, G8BPQ. Each link port adds a KISS TNC, a radio, a feed line and an antenna. Both ends of a link need compatible TNCs. The project documents and helps distribute kits, notably the NinoTNC, a USB TNC designed by Nino Carrillo, KK4HEJ, whose modems include faster speeds and IL2P, a format with forward error correction. The TNC-Pi, which plugs onto the Pi's header, was used in many earlier nodes but has been discontinued. Older TNCs such as the Kantronics KPC-3 can also be used.
The radios are usually single-band mobile rigs or surplus commercial land-mobile units, which can often be found cheaply. Putting different links on different bands, such as the 6-meter, 2-meter and 70-centimeter bands, makes it easier for one node to transmit on one link while receiving on another. Nearby stations may manage with simple indoor antennas, while longer links need antennas mounted high. The project's own guides say that distance and antennas are the hardest part of building a network.
The node can start with a single link and grow later. TARPN's installation scripts set up the Pi and LinBPQ and place a terminal program, G8BPQ's QtTermTCP, on the desktop so the owner can use the node directly.
Operating
Once connected, a TARPN station is a full packet node. Its owner and visitors can connect across the network to other nodes, use any chat or bulletin board applications that LinBPQ nodes offer, and pass messages without any internet connection. Joining an existing network requires a site within simplex range of at least one current node and a modest outlay for a Pi, TNCs and radios. TARPN says its networks can share a region with APRS, Winlink and Broadband-Hamnet mesh networks without getting in their way.