Read Public Transponder Signals | Survival Solutions

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Radio · Receive only

Before you begin

Transponders and automatic identification systems broadcast structured information. The best beginner project is reception and decoding of publicly broadcast ADS-B and AIS—not probing, interrogating or retransmitting.

Safety and legality: Receive only. Never spoof, jam, inject, or interrogate transponders. ADS-B/AIS data can be delayed, incomplete or false; do not use it to navigate vessels, aircraft or rescue operations.

Listen-only receiver chain: appropriate antenna → software-defined radio → decoder → time-stamped local map or log.

Six practical skills

1Distinguish aviation and marine broadcasts 2Select receive-only equipment 3Connect and confirm a signal 4Interpret typical decoded fields 5Validate and account for missing data 6Handle received data responsibly

Field skill 1 / 6

Distinguish aviation and marine broadcasts

Aircraft Mode S/ADS-B Extended Squitter is typically received at 1090 MHz. In the United States, UAT ADS-B also uses 978 MHz. Ships generally use AIS 1 at 161.975 MHz and AIS 2 at 162.025 MHz. Mode S interrogation at 1030 MHz is a separate system, not the normal ADS-B downlink.

Field skill 2 / 6

Select receive-only equipment

Use an RTL-SDR or equivalent receive-capable dongle and a suitable 1090 MHz antenna for ADS-B, or a marine-VHF antenna for AIS; use a computer with sufficient power. An antenna must suit its frequency; expect range to vary with terrain, height and line of sight.

Field skill 3 / 6

Connect and confirm a signal

Install SDR drivers and an established ADS-B decoder (for example readsb or dump1090) or AIS decoder (for example AIS-catcher) from their official project repositories. Choose the correct center frequency, gain and sample rate according to the receiver and decoder documentation. Do not transmit.

Field skill 4 / 6

Interpret typical decoded fields

ADS-B may carry an aircraft identifier, position, altitude, ground speed and heading. AIS may carry an MMSI identifier, navigation status, position, course and speed. A record is meaningful only if its timestamp and validity flags are known.

Field skill 5 / 6

Validate and account for missing data

Use a decoder that checks framing and CRC where applicable. Missing position, random-looking identifiers, stale timestamps and local reception gaps are common. Not every aircraft/vessel is required to broadcast usable position; no single SDR gives complete coverage.

Field skill 6 / 6

Handle received data responsibly

Compare with trusted public reference feeds where permitted, and avoid publishing private or sensitive movements. Respect local radio monitoring and data-sharing laws. For emergencies rely on official rescue services rather than an SDR screen.

Example decoder worksheet

The following labels are illustrative, not a live or verified aircraft record. Log only information a legitimate receiver reports.

Decoder field	What it means	Check before using
Timestamp UTC	Time the local receiver or decoder saw the frame.	Is your clock synchronized, and is this report recent?
Identity (ICAO / MMSI)	Broadcast aircraft or maritime identifier.	It is not proof of a real-world identity.
Latitude / longitude	Reported location when position messages are available.	Look for freshness, quality flags and plausible movement.
Altitude / speed / course	Reported motion fields, which differ between ADS-B and AIS.	Confirm units, reference frame, missing-data indicators.
Message integrity	Frame or CRC validation status.	Reject corrupt records and treat decoded values as advisory.

Related guides

Reference sources

Verify local laws and manufacturer guidance before field use. Information reviewed November 2026.