SWLtools vs PhosphorRTTY

SWLtools: The Companion for Shortwave Listening Enthusiasts SWLtools is an app designed specifically for Shortwave Listening (SWL) enthusiasts who want to enhance their listening experience. It records what you hear, shows you the band, and reads the digital modes that carry text on the air. Whether you are a hobbyist or a dedicated DXer, SWLtools supports your activity from the antenna to the logbook. DECODING THE ON-AIR TEXT MODES Point the app at a signal and it turns it into readable text. - Morse (CW). The app follows the tone by itself and measures the sending speed from the signal, so it keeps up with hand-sent Morse as well as machine-sent. A side panel collects the callsigns it has heard, and each transmission starts on its own line when the operator hands over. - RTTY, in both ITA2 and SITOR-B. - Weather fax (WEFAX). The chart builds up line by line as it arrives, and can be saved straight to your photo library. - ACARS aircraft messages, with the ones carrying a position shown on a map. Decoded text can be saved, reopened later and shared. All times, on screen and in the saved files, are UTC — the way radio logs are kept. SPECTRUM AND WATERFALL If your receiver provides an IQ output, SWLtools displays the real-time spectrum and spectrogram. Visually explore the bands and gain deeper insight into the signals you are receiving. Where the two channels of a USB adapter do not arrive perfectly in step — a common trait of audio codecs — a sample-delay correction removes the mirror image that would otherwise appear beside every signal. AUDIO RECORDING AND STORAGE Easily record and store audio directly from your receiver. Capture signals from around the world and listen to them again whenever you want, or turn a recording into a video to share. OPTIMIZED FOR THE BELKA RECEIVER SWLtools was designed to work seamlessly with the Belka receiver. It is the perfect companion for outdoor listening sessions, letting you record your DX, explore frequencies with the spectrum view, or read a weather fax from the field. The app is optimized for low power consumption when displaying the spectrum and waterfall, making it ideal for portable use. REQUIREMENTS To use SWLtools you need an inexpensive USB audio adapter (ADC/DAC) connected to your iOS device. These affordable dongles typically provide a microphone input and a headphone output, which is enough to record, to decode, and to show a single-channel spectrum. A two-channel audio interface does more: it carries a true I/Q pair, so the spectrum shows the full band above and below the tuned frequency, and it is the only kind that can play the receiver's audio through the iPhone speaker while you listen. The app tells you which class of device you have connected and what it allows, and an audio diagnostics panel shows exactly what iOS is doing with the signal if something does not sound right. Note: please make sure your receiver is compatible with the app's features and that you have the required accessories for optimal performance.

PhosphorRTTY decodes Radio Teletype (RTTY) signals in real time using your iPhone's microphone. Hold your phone near a shortwave radio tuned to an RTTY signal and watch the text appear on screen, character by character, on an authentic phosphor CRT display. No internet connection required. No external hardware. No account. Just your iPhone and a radio. WHAT IT DECODES RTTY is the oldest digital mode in amateur radio — two audio tones representing mark and space, encoding text via the 5-bit ITA2 (Baudot) alphabet or 7-bit ASCII. PhosphorRTTY handles all standard configurations: Baud rates: 45.45, 50, 75, 100 Bd (auto-detected or manual) Shifts: 85, 170, 450, 850 Hz (auto-detected or manual) ITA2 (Baudot) and ASCII modes USB and LSB conventions AUTOMATIC SIGNAL DETECTION The app automatically finds and locks onto RTTY signals: AFC (Automatic Frequency Control) acquires and tracks drifting signals Auto-baud detection identifies the transmission speed Auto-shift detection determines the frequency separation Squelch suppresses noise when no signal is present Or disable any of these and tune manually for full control. FOUR TABS DECODE — The main teleprinter display. Decoded text appears character by character with an authentic mechanical delay. Status bar shows baud rate, shift, mark/space frequencies, and signal lock state. Clear, pause, and session controls. SIGNAL — Live signal analysis. FFT spectrum display (0–4 kHz), scrolling waterfall, mark/space tone indicators, bit period histogram with baud rate markers, and a paper punch tape visualisation of the decoded data stream. LOG — Session history. Every decode session is saved with timestamp, duration, character count, and the full decoded text. Copy, share, or delete individual sessions. CONFIG — All parameters. Audio input gain, decode mode (auto/manual for baud, frequency, and shift), display theme, font size, bell character handling, and RYRY sequence display options. THE DISPLAY Two authentic phosphor CRT themes: Amber (classic teleprinter terminal) Green (military/commercial terminal) Both feature horizontal scanlines, edge vignette, and phosphor glow effects. Monospaced font throughout. RYRY test sequences can be dimmed or hidden to keep the display clean. DSP ENGINE The signal processing is done entirely on-device using a per-sample I/Q quadrature demodulation pipeline: Biquad low-pass filtered I/Q channels for each tone W7AY Automatic Threshold Correction for bit decisions Digital Phase-Locked Loop (DPLL) with per-transition phase correction for timing recovery 512-point FFT for frequency analysis and AFC Asymmetric envelope detection for robust tone tracking through fading Tested against real over-the-air recordings from 20m and 40m amateur bands. Under 1% error rate on clean signals, 4–5% on moderate HF conditions with fixed tuning. WHERE TO FIND RTTY Amateur radio: 14.080–14.099 MHz (20m band), 7.080–7.100 MHz (40m band), 21.080–21.100 MHz (15m band). RTTY contests run throughout the year — during a contest, these frequencies are packed with signals. Maritime and commercial RTTY transmissions can be found across the HF spectrum. A shortwave receiver or SDR with audio output is all you need. REQUIREMENTS iPhone with microphone iOS 17 or later A radio receiver tuned to an RTTY signal (shortwave radio, SDR, or WebSDR audio played through a speaker) No in-app purchases. No subscriptions. No tracking. No network access.