Telegraph key

Telegraph key is a general term for any switching device used primarily to send Morse code. Similar keys are used for all forms of manual telegraphy, such as in ‘wire’ or electrical telegraph and ‘wireless’ or radio telegraphy.

Since its original inception, the telegraph key's design has developed such that there are now multiple types of keys.

A straight key is the common telegraph key as seen in various movies. It is a simple bar with a knob on top and a contact underneath. When the bar is depressed against spring tension, it forms a circuit and allows electricity to flow. Traditionally, American telegraph keys had flat topped knobs and narrow bars (frequently curved). British telegraph keys had ball shaped knobs and thick bars. This appears to be purely a matter of culture and training, but the users of each are tremendously partisan. Straight keys have been made in numerous variations for over 150 years and in numerous countries. They are the subject of an avid community of key collectors. The straight keys used in wire telegraphy also had a shorting bar that closed the electrical circuit when the operator was not actively sending messages. This was to complete the electrical path to the next station so that its sounder would operate, as in the operator receiving a message from the next town. Although occasionally included in later keys for reasons of tradition, the shorting bar is unnecessary for radio telegraphy, except as a convenience when tuning the transmitter.

The straight key is simple and reliable, but the rapid pumping action needed to send a string of dots (or dits as most operators call them) poses some significant drawbacks.

Transmission speeds vary from 5 words (25 characters) per minute, by novice operators, up to about 30 words (150 characters) per minute by skilled operators. In the early days of telegraphy, a number of professional telegraphers developed a repetitive stress injury known as glass arm or telegrapher's paralysis. ‘Glass arm’ or ‘Telegrapher's paralysis’ may be reduced or eliminated by increasing the side play of the straight key by loosening the adjustable trunnion screws. Such problems can be avoided by using a good technique.

Many movies depicting the use of straight keys (e.g., World War II submarine movies, or near the end of the modern science fiction film Independence Day) expose the actors’ lack of training: They invariably lightly tap the key with one or two fingers, when the proper method is to grasp the knob with the thumb and two or three fingers.

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Wikipedia