Semi-automatic key
| Semi-automatic key | |
|---|---|
| Common name | Bug |
| Inventor | Horace G. Martin, New York |
| Patented | 1904 |
| First sold | 1905, by Vibroplex |
| Operation | |
| Dits | Made automatically by a vibrating weighted arm |
| Dahs | Formed one at a time by hand |
| Speed set by | Position of the sliding weights on the arm |
| Typical skilled speed | Over 40 wpm for skilled operators |
A semi-automatic key, almost universally called a bug, is a mechanical Morse key that makes dits automatically while the operator forms each dah by hand. It uses no electronics: a weighted, spring-mounted arm vibrates against a contact to produce a string of evenly spaced dits for as long as the lever is held over. Invented for professional telegraphers in the early 1900s, the bug remains in production and has a loyal following among hams who enjoy its distinctive sound and the skill it takes to master.
History
Sending Morse code all day on a straight key's up-and-down lever could cause a painful overuse injury that telegraphers called "glass arm" or telegrapher's cramp. Inventors looked for keys that would ease the strain, and side-to-side keys such as the sideswiper were one answer. Horace G. Martin of New York City went further with a key that made the dots by itself. After an earlier battery-powered design called the Autoplex, he patented a purely mechanical version in 1904, and keys sold under the Vibroplex name appeared in 1905. The device soon became known as the "bug."
Bugs spread from landline telegraph offices to commercial and military radio; the J-36 bug used by the US military in World War II was based on the Vibroplex Lightning Bug. Many professional telegraphers owned and carried their own keys. Martin added further patents over the following two decades, and Vibroplex pursued makers of imitations, but after the main patents ran out in the 1930s many other companies produced similar keys. Vibroplex still makes the Original model with little change from the early designs, and its older keys are popular with collectors.
How it works
The bug has a single horizontal lever that moves side to side, with a flat thumb paddle on one side of the operator's end and a finger knob on the other. On a standard right-handed bug, the thumb pushes the paddle to the right to make dits, and the index finger pushes the knob to the left to make dahs. A few mirror-image bugs were made for left-handed operators.
- Dits. Pushing the paddle swings the lever and sets a long arm, the pendulum, vibrating. Each swing touches a light spring contact, keying the transmitter once, so a stream of evenly spaced dits continues until the lever is released. A damper then stops the arm so that no stray dits follow.
- Dahs. Pushing the other way closes a separate fixed contact for as long as it is held, so each dah is timed by hand, just as on a straight key.
- Speed. Weights clamped to the pendulum set how fast it vibrates. Sliding them out toward the end slows the dits; sliding them in toward the pivot speeds them up.
Because the hand does only half the work, a practiced operator can send for long periods at speeds a straight key can't comfortably reach, and skilled bug operators can exceed 40 words per minute. The trade-off is that dits and dahs come from different sources, so keeping them in proportion is entirely up to the operator.
Adjustment basics
A bug has several screws and springs that interact, so it pays to adjust them in order. A commonly recommended sequence is:
- Back off the spring tension on both sides to make a starting point.
- Set the pivot bearings so the lever moves freely without wobble.
- Set the dah contact gap for comfortable travel, wide enough that a light touch doesn't make an unwanted dah, and set the dah spring tension.
- Set the dit-side stop so its travel roughly matches the dah side.
- Adjust the dit contact so the dits sound clean, with roughly equal mark and space.
- Slide the weights to set the dit speed, then match the dit-side spring tension to the dah side.
Clean the contacts with silver polish if needed, and never with sandpaper or emery cloth, which leave grit and wear away the contact surface. A bug's dit contact can spark if it switches heavy current, so it is best used with a modern transceiver's low-current keying input.
Using a bug today
Bugs take more practice than either a straight key or a paddle with an electronic keyer, so most operators come to them after learning code on something else. Practicing off the air with the transmitter disabled and the sidetone on, and checking the result with a decoding program, helps build even timing. The Straight Key Century Club counts bugs as eligible keys, and its sprints and events are a natural home for bug operators. Many bug enthusiasts also restore and use vintage keys found at hamfests.