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The WSJT-X network
One of the most fascinating aspects of the WSJT-X ecosystem is the way the software communicates with the outside world.
FT8, FT4, and the other modes in the WSJT-X family do not live in isolation: they generate a continuous stream of information that is collected, interpreted, and visualized by programs such as GridTracker, PSK Reporter, logging software, and propagation analysis tools. To understand how this is possible, one must look into the logic of network data transfer, a mechanism that is both simple in configuration and sophisticated in architecture.
UDP
WSJT-X uses a communication system based on UDP, an extremely lightweight and direct network protocol. Unlike more complex protocols, UDP does not establish a permanent connection between sender and receiver: it simply sends data without acknowledgments, without session setup, and without additional overhead. It is a method that prioritizes speed and continuous data flow, perfectly suited for software that must transmit dozens of small messages every second, without delays and without the need to ensure that every single packet arrives.
In other words, WSJT-X is constantly “talking”, and anyone interested in listening simply tunes in. There is no formal dialogue, but rather a continuous stream of information flowing through the local network.
Every time WSJT-X decodes a signal, changes state, starts or completes a QSO, it generates a structured message that is transmitted via UDP. These packets are not intended to be read by the user, but to be interpreted by external applications that transform them into maps, statistics, logs, or propagation analysis. Thanks to this mechanism, GridTracker can display received stations in real time, PSK Reporter can update its global map, and logging software can automatically record QSOs.
For all this to work, WSJT-X must know where to send the data. Configuration is done in the network settings section, where an IP address and port are specified. In most cases, this address is the local machine, since companion programs run on the same computer. However, WSJT-X’s architecture allows something more interesting: the ability to send data to multiple programs simultaneously, even on different devices. This is where the concept of multicasting comes into play, a networking technique that is little known outside professional environments but extremely useful in digital amateur radio.
Multicasting
Multicasting is a transmission method in which a single data stream is sent to a group of recipients without duplicating it for each one. It is neither an indiscriminate broadcast nor a one-to-one unicast: it is an intelligent middle ground in which devices “subscribe” to a multicast group and automatically receive packets addressed to that group.
In practice, WSJT-X sends a single data stream, but multiple programs can receive it simultaneously, even on different computers within the same local network. It is an elegant, efficient, and surprisingly lightweight mechanism that allows information to be distributed without burdening the network.
Configuring WSJT-X for multicasting is simple: you assign it an IP address from the multicast reserved range (for local networks the 224.0.0.x block is used, typically 224.0.0.1) and a shared port. Companion applications must then be configured to listen on the same address. Once set up, the data stream flows freely to all recipients without further intervention.
This makes it possible, for example, to run WSJT-X on one computer, GridTracker on a second, and logging software on a third-all synchronized and updated in real time.
Multicasting is not just a technical convenience: it is an operational philosophy. It allows information to be distributed naturally, without rigid dependencies between programs. WSJT-X does not need to know who is listening or how many recipients there are-it simply transmits. It is up to the companion applications to decide whether and how to use the data.
This architecture makes the ecosystem extremely flexible. GridTracker can display maps, PSK Reporter can update global propagation data, loggers can record QSOs, and analyzers can study propagation-all in parallel, without WSJT-X doing anything beyond its primary task: decoding signals.
This approach also allows workload distribution across multiple components, leaving all processing power focused on decoding, which can be CPU-intensive when many stations are present.
In this sense, understanding UDP and multicasting is not only a technical matter, but a way of appreciating the deeper logic of modern digital amateur radio: a radio that is no longer confined to a single device, but exists in a distributed, cooperative ecosystem in which each tool contributes to building a richer, more complete, and more aware representation of radio activity.
In summary
WSJT-X enables the creation of a cooperative environment in which each component plays a specific role, yet all share the same language. WSJT-X generates the data stream; the other programs interpret it. The radio becomes part of a broader network in which propagation analysis, logging, and QSO visualization happen naturally and in sync.
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