This real-time real-world Morse decoder and trainer uses the Goertzel algorithm to detect a CW tone of 708 Hz. The program then analyzes the detected tone patterns in order to recognize and decode Morse characters.

A signal with a good SNR and fairly correct (not necessarily perfect) Morse code tone patterns will be decoded flawlessly; for example, a signal taken directly from a computer, or a 9+ signal over the radio. The speed can exceed 50 standard words per minute (WPM). However, operator variation (individual sending styles) and atmospheric noise complicate things. On the always noisy HF radio bands, where signals can be very weak and often overlap, the decoder is inferior to a trained human who employs experience and context in order to make sense of the mess. Still, at any given time, one will find many real CW transmissions that this decoder can decode, although with weaker signals the results will vary in accuracy and completeness. All in all, a good number of signals are actually copyable in the most practical sense, with transient errors that are easily spotted and resolved, much like when you're copying by ear on a noisy band.

The purpose of this decoder is not to discourage amateur radio operators from learning Morse code but, on the contrary, to stoke their curiosity and give them a fun learning experience.

The decoder automatically adjusts to the transmission speed. (When the speed changes sharply, it may take a second or two.)

The training mode helps the operator acquire a good sending style. The LCD indicates the speed and the characters sent (if correct). 

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https://yu2zz.wordpress.com/2026/07/11/arduino-based-dsp-morse-decoder-and-trainer-on-a-custom-pcb/