This file contains ambiguous Unicode characters

This file contains Unicode characters that might be confused with other characters. If you think that this is intentional, you can safely ignore this warning. Use the Escape button to reveal them.

Introduction

Morse RX is a Morse code receiver that automatically detects and decodes incoming CW signals. Tune to the signal frequency and wait for clear audio — the app handles tone frequency detection, WPM estimation, and character decoding without manual configuration.

The decoder uses automatic tone and speed detection, which may take a few moments to lock onto a signal. Decoding quality depends heavily on signal clarity.

Controls

Top row:

• Frequency: Click to open the numeric keypad, or use the rotary encoder for fine tuning.
• AMP: RF preamplifier — 0 = off, 1 = on (+14 dB). Avoid enabling near strong signals.
• LNA: Low Noise Amplifier gain (0–40 dB).
• VGA: Variable Gain Amplifier / baseband gain (0–62 dB).
• Volume: Audio output level.

Second row:

• Squelch (0–99): Sets the squelch level. Signals below this threshold are ignored. Adjust to suppress background noise without cutting off the desired signal.
• Mode: Selects the demodulation mode — AM/CW, NFM, AM/DSB, AM/USB, or AM/LSB. Use AM/CW for standard HF CW, NFM for VHF/UHF Morse beacons.
• Speed: XX wpm: Displays the estimated receive speed in words per minute. This is calculated automatically from the detected dit/dah timing. If decoding goes wrong the value will visibly adapt as the algorithm self-corrects.

Third row:

• Log checkbox: Enables logging to a daily file in the LOGS/ directory on the SD card. Each log session is stamped with a timestamp header and the selected mode.
• Tone: XXXX Hz: Displays the detected audio tone frequency of the incoming Morse signal. The colour indicates whether the tone is in a good range for decoding:
  • Green — 580–1220 Hz: optimal range
  • Yellow — 400–580 Hz or 1220–1400 Hz: acceptable but at the edge
  • Red — below 400 Hz or above 1400 Hz: outside the reliable decoding range; results will be poor

Fourth row:

• Last seq.: Shows the most recently detected dit/dah pattern before it was decoded into a character, useful for debugging weak or noisy signals.

Decoded text console:

The large area in the lower half of the screen shows the decoded characters. The colour of each character indicates the decoder's confidence:

• Green — confidence ≥ 90%: high confidence
• Yellow — confidence 80–90%: moderate confidence
• Red — confidence < 80%: low confidence, likely incorrect
• White — spaces and unmatched sequences

Bottom:

• CLR: Clears the decoded text console.

Tips for best results

The decoder requires a clean, steady audio tone in the 400–1400 Hz range. Before starting:

• Adjust frequency so the signal produces a clear audio tone — listen with the speaker enabled.
• Use a narrowband mode (AM/CW or NFM) and set gain so the signal is strong but not clipping (a clipping warning appears on screen if the input is saturated).
• Keep the scan range small and avoid strong nearby interferers.
• If the tone frequency display shows red and jumps around, there is too much noise or the wrong mode is selected.

Settings persistence

The selected demodulation mode is saved automatically and restored on next launch. Settings are stored in SETTINGS/rx_morse_radio.ini on the SD card.