Audio Recording Guide
Edit on GitHubRecording the beacon's Morse output cleanly: levels, input types, and the setup that decodes every time.
Audio Recording Guide
Recording the beacon’s audio is how you verify, archive and share its transmissions. The failures are almost always levels, and this page is the fix.
The signal the beacon produces
The audio jack outputs the keyed 700 Hz square wave at 3.3 V logic level (see Audio Tone Details). That is far hotter than a microphone input expects, and too “digital” for a line input.
The input ladder
| Input | Level | Result with a direct connection |
|---|---|---|
| Mic input | ~5 - 50 mV | Clipping, distortion |
| Line input | ~0.3 - 1 V | Acceptable to hot |
| Speaker/headphone input | 3.3 V class | Perfect, if the recorder has one |
The honest setups:
- A recorder with a headphone/speaker input, direct cable: cleanest.
- A phone mic input with an inline attenuator (two resistors, see Audio Troubleshooting).
- The beacon’s own buzzer, recorded at a distance: works, but captures the room too.
The recording workflow
- Set the recorder level so the waveform peaks at about 70%.
- Trigger one burst (see Serial Monitor Guide for the
tx nowcommand). - Play back and decode with software (see Morse Decoder Tools) or by ear (see Reading CW by Ear).
- A decode on the first take means the levels are right.
The radio bridging version
The same audio can be fed into a handheld radio’s mic input to relay the beacon’s signal (see Two Way Build). The rule changes: the radio’s mic gain must be turned down, because the beacon’s level will overdrive it and splatter adjacent channels.
Related pages
- Audio Troubleshooting for the faults
- Audio Tone Details for the specs
- Morse Decoder Tools for decoding