APRS Δ

See the signal. Inspect the packet.

A focused 1200-baud APRS receive debugger. Drop in radio audio or record one run, then inspect Bell 202 tones, NRZI bits, HDLC sync, AX.25 framing, and basic APRS structure.

Built with ideas and assets from Dire Wolf hessu/aprs-symbols wa8lmf/TNCtest

★ Star APRS Δ on GitHub Project link coming soon

Choose WAV, MP3, M4A, OGG, or FLAC Up to the first 5:00 are analyzed

Maximum duration

minutes

Run diagnosis

Waiting for one run

Frames — valid CRC

Longest sync — HDLC flags

Tone confidence — median symbol decision

DEMODULATOR OUTPUT

Mark vs space

1200 Hz 2200 Hz

capture startscroll horizontallyend

PHY checks

Run a capture to populate checks.

TIME / FREQUENCY

Spectrogram

500 Hz 3000 Hz

500 Hz at bottompacket markers jump to details3000 Hz at top

NRZI bitstream

Allowed sync errors

Show full NRZI capture bitstream 0 bits

AX.25 NRZI · tone change = 0 · no change = 1 · sync ignores display boundaries 0 bits

No tone decisions yet.

Export contains only contiguous 0/1 characters—no spaces or line breaks. Highlighted sync is detected after NRZI at any capture bit offset.

Packets

May contain errors consult the latest APRS documentation

No decoded frame yet

A CRC-valid AX.25 UI frame will appear here with basic format checks.