What Port 1939 Is
Port 1939 is registered with IANA to jvserver — the server component of Jetvision's ADS-B aircraft tracking system.1
Jetvision is a German company that builds the Radarcape, a high-precision receiver for ADS-B signals. ADS-B (Automatic Dependent Surveillance–Broadcast) is the system modern aircraft use to broadcast their identity, position, altitude, and speed. Every commercial flight you've ever taken was squawking this data into the air. The Radarcape listens for it.2
The JetVision server software aggregates this data, processes it, and serves it to clients — aviation enthusiasts, flight tracking networks, and professional air traffic monitoring operations. Port 1939 is where that server listens.
What Range This Port Belongs To
Port 1939 falls in the registered ports range: 1024–49151.
This range sits between the well-known ports (0–1023, reserved for fundamental Internet services) and the ephemeral ports (49152–65535, used for temporary client connections). Registered ports are officially assigned by IANA to specific applications and services — though the assignments range from globally critical infrastructure to deeply niche software used by a few thousand people worldwide.3
Jetvision's assignment is firmly in the latter category. IANA maintains it. Almost no one outside aviation tracking will ever encounter it.
Will You See This Port?
Almost certainly not, unless you're running Jetvision's software or connecting to a Radarcape receiver.
If you do see traffic on port 1939 unexpectedly, it's more likely a misconfigured application or a port scanner than an aircraft tracking server. The JetVision server is purpose-built for specific hardware and not widely deployed.
How to Check What's Listening on Port 1939
If you want to know whether anything is using this port on your machine:
macOS / Linux:
Windows (Command Prompt):
Linux (alternative):
If nothing is listening, these commands return empty. That's the expected result on almost every machine on Earth.
Why Unassigned-Adjacent Ports Matter
Port 1939's Jetvision assignment illustrates something worth understanding about the port system: the registered range is enormous, and most of it is quiet. Of the ~48,000 registered ports, only a fraction carry meaningful traffic at any given moment.
This has security implications. Applications that want to avoid the scrutiny that well-known ports receive sometimes operate in the quiet registered range. A process listening on an unusual port in this range isn't necessarily malicious — but it's worth knowing what it is. The legitimate users of port 1939 are tracking aircraft. Anyone else using it is doing something they chose to obscure.
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