💡 Key Features

The SDR panadapter — live scope and scrolling waterfall with click-to-tune, DX / broadcast-station markers, and a navigator overview, right in the browser

🎮 Frequency Tuning

Mouse/Desktop

• Click any digit to select it (highlighted)
• Scroll mouse wheel over any digit to change it
• Arrow Up/Down keys change the selected digit
• Arrow Left/Right keys move selection between digits

Touch/Mobile

• Tap any digit to select it
• Tap arrows to increase/decrease selected digit
• Long-press arrow buttons for continuous tuning

🌈 Spectrum & Waterfall Display

The web client includes a real-time spectrum analyzer and waterfall display for visualizing audio:

The Visualization tab — real-time spectrum curve over a scrolling waterfall of the decoded audio

Display Components

• Spectrum Analyzer – Real-time frequency curve at top showing current signal levels
• Waterfall – Scrolling spectrogram below showing signal history over time

Controls

• Show/Hide – Toggle button to show or hide the display
• Gain slider – Adjust brightness/sensitivity (0.5x to 5x)
• Palette (new 2026-10) – The waterfall’s colours, from the same palette list as the SDR tab, with its own choice remembered by the browser

Tuning the Decoder From the Waterfall

The audio waterfall is the primary way to place a decoder on a signal:

• Hover – A dim ghost cursor follows the pointer, reading out the frequency under it, and — for modes you can retune — a preview of the decoder’s passband centred on the cursor, so you can see how it would sit on the signal before you commit.
• Click to place – The decoder moves there. The marker then shows where the decoder actually landed, so if the value was out of range you see the clamp rather than a marker that quietly disagrees. Only PSK31, Olivia and NAVTEX have a centre frequency to move; in other modes the click just parks the marker.
• Decoder passband – A translucent rectangle showing the span the active decoder is listening across: Olivia’s exact bandwidth (16/500 = 500 Hz), PSK31’s symbol rate, RTTY’s live auto-detected mark/space rails, and the fixed tone rails for NAVTEX, APRS, SSTV, WEFAX and CW. It is the nominal occupied span — an alignment aid, not a measured bandwidth. The server resolves it and broadcasts it, so every client agrees.
• Nothing drawn for the bridged modes – FT8, WSPR and JS8 show no passband: those are decoded by WSJT-X / JS8Call, not by ShackLink, so there is nothing honest to draw.

Usage

1. Start audio streaming first
2. Click Show in the Waterfall section
3. Adjust gain slider for optimal visibility

The SDR waterfall: three modes and thirteen palettes

New in 2026-08.

The SDR tab’s waterfall — the panadapter, not the audio display above — now carries the same three pane modes the desktop applications have, rendered in WebGL2 in your browser:

• 2D — the classic flat scroll.
• 3D — the whole pane becomes a terrain built from spectrum history.
• Split — terrain on the top half, the flat scroll underneath, joined on one shared instant: both show now at the seam, and history runs away from it in both directions.

The mode is a per-browser preference in localStorage; it costs no extra bandwidth and needs no server change, because the spectrum stream already reaches the page. Overlays follow it — the tuning needle, a draped marker trace, the five passband styles, the frequency graticule and the time axis are all drawn onto the terrain, with the graticule fed from the same ticks the flat scale strip draws so the two cannot disagree.

The waterfall also has thirteen named palettes now — Classic (blue), Classic (green), CoolWarm, Viridis, Plasma, Inferno, Grayscale, Neon (cyan), Signal (teal), Semaphore, Rainbow, and two light ones, Paper (light) and Blueprint (light) — the same set, by name, that the desktop uses. Before this the browser had one hardcoded gradient, and it was not even the same gradient as the desktop’s default, so a palette of a given name genuinely rendered different colours here. Nothing about the palette rides the wire: it is a per-client display preference, like gain and contrast.

Changed 2026-10: Display Gain and Contrast now colour only the waterfall, as on the server. The spectrum trace above it is a straight dB plot of the amplitude window, so 10 dB always looks like 10 dB and strong signals are no longer flattened against the top; the floor control still moves it.

📈 Auto-Identify & RDS

Auto-Identify

Auto-Identify labels each detected signal on the SDR display with a small colour-coded chip over its carrier; hover for the top candidate modes with confidence, plus measured frequency, bandwidth and SNR. The scan runs on the server, so the browser renders exactly the same chips as the desktop client and the mobile app.

RDS

RDS auto-activates whenever the SDR demodulator is in WFM — it is not a decode mode you select. It decodes the 57 kHz subcarrier for the station name (PS), programme identification (PI), RadioText, programme type, clock time, and traffic/network data.

The web client surfaces it as an RDS strip that appears between the radio control card and the tabbed work area whenever RDS data is present, carrying the station name, RadioText, and a programme-type badge, plus indicator dots for the pilot PLL (P), block sync (S), and FM stereo (ST).

🎥 Audio Recording

Record the audio stream to WAV or MP3 files:

Recording Controls

• Format selector – Choose WAV or MP3 format
• Record button – Start/stop recording
• Duration display – Shows elapsed recording time

How to Record

1. Start audio streaming first
2. Select desired format (WAV or MP3)
3. Click Record to begin
4. Click Stop to end and download

Format Comparison

📡 TX (CW / RTTY / PSK31 / Olivia / APRS + voice)

The TX tab is the text and voice transmitter. Text modes are server-synthesized — the browser sends what you typed and the server’s TX engine generates the audio — so they work from any browser on any connection.

1. Pick a mode: CW, RTTY, PSK31, Olivia, APRS, or Voice
2. Click Key to take the TX lock, type into the compose box, then Send (or Ctrl+Enter). Unkey when done; Abort bails out mid-transmission.
3. Level sets the TX audio level, mirrored to every client through the TX:CONFIG protocol
4. APRS: one send is one AX.25 packet — use >status text, LAT,LON:comment, or >ADDRESSEE:text. The source callsign comes from the server’s settings, not the browser.
5. Olivia: format, family and centre frequency follow the server’s live Olivia decoder settings — TX matches RX, which is how the QSO works. Contestia folds text to uppercase server-side.
6. Voice: press and hold Push To Talk. Releasing unkeys, and so does leaving the page or losing window focus.

Since 2026-10 Key, Send, Unkey, Abort and the status sit in a column to the right of the compose and Sent boxes (a row under them on a phone), and the mode buttons take a line of their own when the page is narrow.

📜 Slot Decoders Tab

Every per-slot decoder at once

Each of the server’s SDR slots can run its own decoder, on its own audio, independently of the Decoder tab. The Slot Decoders tab shows what all of them are hearing: a lane per slot for the character and line modes (name, decoder mode, listen frequency, running transcript) and a table of FT8/FT4 records. Turn a slot’s decoder on with the Decode picker on the SDR tab; this tab is a view.

Three details that are deliberate rather than missing: a lane retires dimmed when its decoder stops, so the transcript stays attributable; a blank SNR on an FT8/FT4 row means the slot’s gain moved under that cycle, not that the value is unknown-and-zero; and there is no click-to-tune, because a per-slot decode is keyed by its slot and none of the modes captures an on-air frequency to tune to.

🗺️ Propagation Map

The Map tab shows a live greyline propagation map — a world map with the day/night terminator drawn across it. The greyline (the band of twilight sweeping the globe) is where long-haul HF propagation is often at its best, so it’s a quick visual cue for when and where the bands are likely to open. Like every other tab, the radio control card stays pinned above it. It is the same map the server and the desktop client show, served by the server.

New 2026-10: a Flat | Globe switch in the Layers panel turns it into a 3-D globe you can spin and zoom (loaded only the first time you pick it), with new layers: a MUF map from the server’s propagation model, greyline DX with open and close times, ionosonde readings, D-region absorption, spot-density columns and hop paths (globe only), satellites with their next passes, the Moon and EME windows, and city lights. Times can be UTC or local and distances km or miles. The Worked DXCC layer needs a logbook, which the browser does not have, and says so.

The Map tab — greyline propagation map with the day/night terminator across the world

🌐 Browser Compatibility