Listening to military and air traffic radios with SDR: legal and technical insights

With the widespread adoption of SDR (Software Defined Radio) technology, it has become possible for almost anyone to explore the radio spectrum from home. With an inexpensive SDR receiver and the right software, you can receive a wide variety of signals — including civil aviation and even some military radio traffic.

But where are the legal boundaries? What is allowed and what is not? What technical setups are needed for effective reception? How can you avoid misunderstandings or violations of the law?
In this article, we provide a comprehensive overview of the topic — suitable for beginners and advanced users alike.

What is SDR and why is it popular for monitoring aviation and military radios?

SDR technology refers to software-controlled radio receivers, where traditional hardware functions (filtering, decoding) are handled by software. In practical terms:

  • A single receiver can monitor a wide frequency range.

  • The receiver is flexibly programmable — no need for multiple radios for different bands.

  • With free or affordable software, you can decode almost any modulation.

Why is it popular for monitoring aviation and military traffic?

  • Civil aviation radios (VHF band, AM modulation) are easily accessible.

  • Some military radio traffic is transmitted unencrypted in special bands.

  • It is an exciting hobby for aviation enthusiasts, radio amateurs, and spotters.

  • SDR also provides real-time spectrum visualization.

Which frequencies are used for air traffic?

Civil aviation (VHF)

  • 118 – 137 MHz band

  • AM modulation

  • Air Traffic Control (ATC), tower communications, ground services, pilot-to-pilot communications.

Aviation data transmission (ACARS)

  • 131.725, 131.525, 131.825 MHz (varies)

  • Digital data (requires ACARS decoding software).

Aircraft tracking: ADS-B

  • 1090 MHz

  • Digital signal (Mode-S ADS-B), real-time aircraft position — perfectly decodable with SDR.

HF aviation communications

  • 2 – 30 MHz band

  • Long-distance flights: voice communications and digital data.

Which frequencies are used for military radio traffic?

Military frequencies vary by country, but in Europe/NATO regions you will typically find:

VHF military air traffic

  • 225 – 400 MHz band (UHF military aviation band).

  • AM modulation.

  • Used by military aircraft, NATO AWACS, air defense units.

Military HF traffic

  • 3 – 30 MHz band.

  • Long-range communications, expeditionary forces.

  • Often digital or encrypted (ALE, STANAG protocols).

Other special frequencies

  • VLF/LF bands: submarine communications.

  • SATCOM: satellite-based military communications.

Important: some military signals are encrypted — decrypting such signals is illegal (more on this below).

What SDR hardware do you need?

Entry-level SDR receivers

  • RTL-SDR v3 (~30-40 USD)

    • 24-1700 MHz — suitable for civil aviation and UHF military traffic.

  • Nooelec NESDR or similar.

Intermediate SDR receivers

  • Airspy Mini, Airspy R2

    • Higher bandwidth, lower noise floor.

  • SDRplay RSPdx

    • 1 kHz – 2 GHz+ — ideal for aviation + HF + UHF military bands.

Professional SDR systems

  • HackRF One (half-duplex, 1 MHz – 6 GHz)

  • LimeSDR Mini

  • USRP B200 / B210 — professional software-defined radio for research.

What software should you use?

Basic SDR receiver software

  • SDR# (SDRSharp) — Windows, great for beginners.

  • SDR++ — Windows, Linux, Mac.

  • HDSDR

  • CubicSDR

Aviation-specific software

  • ADSBSpy, dump1090 — for ADS-B reception.

  • ACARSDec, JAERO — for decoding ACARS data.

Advanced decoding tools

  • DSDPlus — for digital voice decoding (TETRA, P25, etc.).

  • MultiPSK, Fldigi — for HF digital modes.

Legal overview: what is allowed and what is not?

European Union and local laws (example: Hungary)

Receiving radio signals is generally not prohibited, unless:

  • The signal is encrypted or protected (e.g. encrypted military comms, GSM networks, police).

  • You rebroadcast, share, or publish the received content — that may be illegal.

Civil aviation

  • Monitoring civil aviation bands is a widely accepted hobby globally.

  • In Hungary and across Europe, many hobbyists and spotters monitor public air traffic.

  • Streaming or rebroadcasting air traffic may be legally questionable.

Military radio

  • Monitoring unencrypted military air traffic (e.g. UHF AM) is not illegal per se, but:

    • Recording, sharing, or publishing military communications may violate national security laws.

    • Decrypting encrypted signals is explicitly illegal.

Summary of legal/ethical guidance

Activity Allowed?
Listening (unencrypted) Yes
Decoding unencrypted signals Yes
Streaming or publishing military traffic No
Decrypting encrypted signals No

Ethical considerations

As a responsible radio listener:

  • Respect the law.

  • Do not share positions, military maneuvers, sensitive information.

  • For private hobby use, monitoring is perfectly fine.

  • Avoid public streaming of military bands.

Useful resources and communities

Hungarian communities

  • Amateur radio clubs

  • SDR Hungary Facebook group

  • Satellite monitoring groups

International communities

  • RTL-SDR.com

  • Signal Identification Wiki — for identifying unknown signals.

  • LiveATC.net — civil aviation (where legally permitted).

SDR offers an incredible opportunity to explore the radio spectrum from home.
Monitoring aviation traffic is a great entry-level hobby — including civil and some UHF military air traffic. But always be aware of the legal and ethical boundaries.

By using SDR responsibly and legally, it can remain an exciting and educational hobby for years to come.

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