APRS decoder for 144.800 MHz in the browser
APRS packets on 144.800 MHz are sent at 1200 Bd. Signal-Pirat decodes them from a recording or live via the receiver output and shows position, message, status or telemetry. For practice, you can create your own packets as audio.
Open in the browser
No installation, no sign-up needed.
What the page does
- Decode recordings up to 10 minutes, counting rejected packets
- Live reception via microphone or line input
- Shows position, course, altitude, message, status, telemetry
- Own packets as practice audio and WAV
- Own development following AX.25 and the APRS specification, no installation
Background
APRS uses Bell 202 AFSK: 1200 Hz for a one, 2200 Hz for a zero, zeros as tone changes (NRZI). The data is carried in AX.25 frames with flags, bit stuffing and a CRC-16 checksum. The decoder filters the signal, compares both tones over one bit and recovers the clock with a digital PLL. In test runs all packets are decoded from about 14 dB SNR in a 3 kHz channel.
In practice
How it works: set the receiver to 144.800 MHz FM, open the squelch or set it just above the noise and connect the speaker or data output to the computer's line or microphone input. Choose a volume that does not overdrive the input. The statistics show how many frames failed the checksum – a good indication of level or reception quality.
Frequently asked questions
Do I need a special receiver?
An FM receiver or radio on 144.800 MHz with audio output is enough; an SDR works too.
Can I transmit with it?
Signal-Pirat does not transmit. Transmitting requires an amateur radio licence and your own callsign.