You certainly know the oldest encoding language for radio transmissions, don't you. You are right, it is the morse code.
Manually decoding morse code (meaning by hearing and mentally translating it into letters and words) is not highly sensitive to background noise
and other signal disturbances since what we only need is to be able to differentiate the long tones (dashes) from the short tones (dots) and of course the pause between them.
Electronic Circuits volume 1.0 - Circuit Nr. 40
The complete data of the electronic circuit described above can be found in the following book and is available from Amazon.com.
Click on the image to view the book.