Telegraph key

Telegraph key (sometimes also Morse key) is a generic term for any switching device used primarily to send Morse code. Similar keys are used for all forms of manual telegraphy. Two common uses include the electrical telegraph over wires which activates a Telegraph sounder and radio telegraphy. Several variants exist.

Table of contents
1 Straight Keys
2 Alternative key designs
3 Odd uses

Straight Keys

A straight key is the common telegraph key seen in old 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.

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 are limited to around 20 words per minute, and in the early days of telegraphy a number of professional telegraphers developed a repetitive stress injury known as glass arm or telegrapher's paralysis.

Alternative key designs

The first widely accepted alternative key was the sideswiper or sidewinder, sometimes called a cootie key. This key uses a side-to-side action with contacts in both directions and the arm spring-loaded to return to center. A series of dits could be sent by rocking the arm back and forth. Since few people are able to make the leftward and rightward motions identically, the alternating action produces a distinctive rhythm or swing. Although the sideswiper is seldom seen or used today, nearly all advanced keys use some form of side-to-side action.

Undoubtedly the most popular side-to-side mechanical keys is the semi-automatic key or bug, sometimes known by as a Vibroplex key, after the company that first manufactured them. When the paddle is pressed to the left it makes a continuous contact suitable for sending dashes (or dahs, as most operators call them). When the paddle is pressed to the right, a horizontal pendulum is set into motion which rocks against the contact points, sending a series of short pulses (dits) at a speed which is controlled by the position of the pendulum weight. A skilled operator can achieve sending speeds of 60 to 80 words per minute with a bug.

Like the bug, the electronic keyer operates sideways. When pressed to one side the electronics generate a series of "dahs" and when pressed the other way, a series of "dits". Most electronic keyers include a dit memory function which frees the operator from the need to perfectly time his transitions in the sequence dah-dit-dah. With dit memory, if the operator's keying action is about one dit ahead of the actual transmission, the keyer's output for each letter will be machine-perfect. An iambic keyer sports dual paddles, one for dit and one for dah; pressing both at the same time produces an alternating dit-dah-dit-dah sequence. Electronic keyers allow very high speed transmission of code.

Odd uses

Telegraph keys were once used in the study of operant conditioning with pigeons. Starting in the 1940s, initiated by B. F. Skinner at Harvard University, the keys were mounted vertically behind a small circular hole about the height of a pigeon's beak in the front wall of an operant conditioning chamber. Electromechanical recording equipment detected the closing of the switch whenever the pigeon pecked the key. Depending on the psychological questions being investigated, keypecks might have resulted in the presentation of food or other stimuli. Modern pigeon response keys are specially made switches but are still called "keys" due to their origins as telegraph keys.

copyright 2004