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Although a few abbreviations (such as SX for "dollar") are carried over from former commercial telegraph codes, almost all Morse abbreviations are not commercial codes. From 1845 until well into the second half of the 20th century, commercial telegraphic code books were used to shorten telegrams, e.g. PASCOELA = "Locals have plundered everything from the wreck."
A contemporary Morse code chart. Here is a more up-to-date version, ca. 1988: Other visual mnemonic systems have been created for Morse code, mapping the elements of the Morse code characters onto pictures for easy memorization.
The Alexanderson alternator works similarly to an AC electric generator, but generates higher-frequency current, in the very low frequency (VLF) radio frequency range. The rotor has no conductive windings or electrical connections; it consists of a solid disc of high tensile strength magnetic steel, with narrow slots cut in its circumference to ...
Vibrators are relatively unreliable as electromechanical components of limited life, buzz audibly, and produce radio interference. A few radios used a bulkier and more expensive motor-generator or motor-alternator set called a "dynamotor" that spun a high-voltage generator or alternator using a 6- or 12-volt DC motor. Filaments were powered ...
Morse code can be transmitted in a number of ways: Originally as electrical pulses along a telegraph wire, but later extended to an audio tone, a radio signal with short and long tones, or high and low tones, or as a mechanical, audible, or visual signal (e.g. a flashing light) using devices like an Aldis lamp or a heliograph, a common ...
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A receiver is tuned to a Morse code signal, and the receiver's intermediate frequency (IF) is f IF = 45000 Hz. That means the dits and dahs have become pulses of a 45000 Hz signal, which is inaudible. To make them audible, the frequency needs to be shifted into the audio range, for instance f audio = 1000 Hz.
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