SWLTools records what you hear, shows you the band, and reads the digital modes that carry text on the air — Morse, RTTY, weather fax and aircraft messages. Connect any receiver through a USB audio adapter and see what is being said, not just what is being transmitted.
Point the app at a station and the text appears while the audio plays. No presets to hunt for: the app finds the tone, measures the speed, and follows the signal you tuned even when another one crosses it.
The app locks onto the tone by itself and measures the sending speed from the signal, so it follows an operator's hand as well as a machine. Each transmission starts on its own line when the turn is handed over.
A side panel collects the callsigns heard — and leaves out the ones that were only another callsign read wrong, which is the difference between a log you can trust and a list you have to check.
Marine bulletins, press agencies, NAVTEX. Set shift and speed, press Auto to land on the two tones, and the text runs as it arrives.
The chart builds up line by line as it comes in, the way it did on paper. When it is complete you can save it straight to your photo library.
The short data bursts airliners exchange with the ground, checked against their own CRC so that what you read arrived intact. The ones carrying a position are placed on a map.
Decoded text can be saved, reopened later and shared. Every time shown or written down is UTC, the way radio logs are kept.
Filmed with a real receiver and a USB audio adapter — nothing simulated.
RTTY, decoded live
Finding a signal on the band
Around the decoders sits everything needed to find a signal and keep it: a spectrum you can read, a waterfall that remembers, and an audio chain that tells you what it is doing.
GPU-accelerated FFT spectrum display rendered with Metal. See signal strength across the full audio bandwidth at a glance, with adjustable scaling and smoothing.
Scrolling waterfall with multiple color themes shows signal history over time. Frequency cursors let you mark and monitor specific signals. Ideal for spotting intermittent transmissions.
Built-in FIR bandpass filter with adjustable center frequency and bandwidth. Isolate a single signal before decoding to improve accuracy in crowded band conditions.
Feed the I/Q output of your receiver into a two-channel interface and the spectrum opens up on both sides of the tuned frequency. A sample-delay correction removes the mirror image that USB audio codecs would otherwise put beside every signal.
Works with the built-in microphone, USB audio dongles, or Bluetooth audio sources. Plug your receiver's headphone output into any compatible adapter and start monitoring.
With a two-channel audio interface you can listen to the receiver through the iPhone while the app analyses it. The cheap single-channel adapters cannot: iOS drops them when sound is sent to the speaker, and the app tells you so instead of letting you wonder.
A panel that shows what iOS is actually doing with your signal: route, format, buffers, dropped samples — and whether the monitor has quietly taken the dongle away and left you listening to the room.
Record what you hear, play it back, and turn a recording into a video to share. Decoded texts and received charts are saved too, and go out through the usual share sheet.
Whether you're listening to shortwave broadcasts, chasing DX stations, or monitoring maritime and aviation radio, SWLTools gives you the tools professionals use — right on your iPhone.