Reviewed September 24, 2026 against source v1.7.41. Features and fixes are labeled by version. Check release availability.
Watch a channel, not an entire band
Available in v1.7.40 and later. ACTIVITY WATCH monitors RF power inside the selected receiver's tuned passband. It learns that channel's quiet background and reacts to a sustained increase. It is not speech recognition, a protocol decoder, or proof of a particular transmitter.
- Tune an audio-capable receiver to the channel and choose the correct demodulation mode and filter width.
- Allow a quiet interval so the watch can learn the background.
- Open Settings > Alerts > Channel Activity Watch and choose what happens on activity.
- Press ACTIVITY WATCH beside PATTERN on that receiver's card. Press it again to stop watching.
Choose the response
| Settings control | Behavior |
|---|---|
| Play it over the speaker | Temporarily enables that receiver's audio while activity is present. Audio you enabled manually stays on afterward. |
| Alert sound | Plays the channel's short low-high tone. This is separate from NOTICE, ALERT, CRITICAL, and new-aircraft sounds. |
| Alert dialog | Shows the receiver and frequency. It respects the event-alert switch, popup cooldown, and temporary mute. |
| Record the audio | Saves demodulated audio and metadata, independently of the continuous session RECORD button. |
Threshold and hold time
Activity threshold defaults to 8 dB above the channel's learned background and can be set from 3 to 40 dB. Lower values catch weaker changes but also more noise. The detector requires about 250 ms above threshold before declaring activity and uses hysteresis to avoid rapid on/off switching.
Hold after signal drops defaults to 2 seconds and can be set from 0.5 to 30 seconds. It keeps short pauses within one transmission. Changing frequency, mode, or channel width resets the learned channel background. A constant carrier already present when learning begins can become background rather than a new event.
Find the recordings
Use OPEN ACTIVITY RECORDINGS in Settings > Alerts. Files are stored under your selected data folder in Activity\YYYY-MM-DD\, grouped by the local date. With the default data folder this is Documents\SPECTER SDR\Activity\.
Each capture is a 48 kHz mono, 16-bit WAV plus a JSON metadata file containing receiver identity, frequency, mode, timing, peak excess over background, and any truncation flag. The recorder retains approximately 1.5 seconds of available pre-roll. A just-enabled watch may not yet have that much audio buffered.
A continuously active channel is capped at about 10 minutes of audio per capture; it is not automatically split into an unlimited series of files. The capture is finalized when activity ends, the watch stops, or the application closes normally. Keep the JSON beside its WAV.
Use a receiver that stays on the channel
A scanner, Search Director, Decoder Lab profile, linked tuning, or periodic ADS-B assignment can move a receiver. For a reliable channel watch, dedicate a radio to the channel instead of retuning it for other work. The watch follows tuning changes; it does not reserve the radio.
TinySA analyzers have no demodulated audio and are excluded from channel activity watching. Use their spectrum and analyzer alerts instead. Activity recordings are also distinct from class-qualified RF event clips and raw IQ captures.
Troubleshoot missed or repeated activity
- Confirm the watch is enabled on the intended receiver and the mode and filter cover the signal.
- If a steady carrier was present during learning, test with a quiet interval followed by a new transmission.
- For repeated noise detections, increase threshold or hold time. Lowering squelch alone does not change the RF detector's threshold.
- If a WAV has no useful audio, verify demodulation, squelch, audio delivery, and disk access. RF activity does not guarantee intelligible speech.
- In v1.7.41, the live activity tone observes its repeat gap rather than behaving like a Settings preview. See version availability.