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Tikker
A tikker, alternately spelled ''ticker'', was a vibrating interrupter used in early wireless telegraphy radio receivers such as crystal radio receivers in order to receive continuous wave (CW) radiotelegraphy signals. In the early years of the 20th century, before modern AM or FM radio transmission was developed, radio transmitters communicated information by radiotelegraphy; the transmitter was switched off and on by the operator with a telegraph key, producing pulses of radio waves, to spell out text messages in Morse code. Around 1905 the first continuous wave radio transmitters began to replace the earlier spark transmitters. The Morse code signal of the spark transmitter consisted of pulses of radio waves called damped waves which repeated at an audio rate, so they were audible as a buzz or tone in a receiver's earphones. In contrast the new continuous wave transmitters produced a signal consisting of pulses of continuous waves, unmodulated sinusoidal carrier waves, wh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Continuous Wave
A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or particle accelerator having a continuous output, as opposed to a pulsed output. Continuous wave is also the name given to an early method of radio transmission, in which a sinusoidal carrier wave is switched on and off. Information is carried in the varying duration of the on and off periods of the signal, for example by Morse code in early radio. In early wireless telegraphy radio transmission, CW waves were also known as "undamped waves", to distinguish this method from damped wave signals produced by earlier ''spark gap'' type transmitters. Radio Transmissions before CW Very early radio transmitters used a spark gap to produce radio-frequency oscillations in the transmitting antenna. The signals produced by these spark-gap transmitters c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Detector (radio)
In radio, a detector is a device or circuit that extracts information from a modulated radio frequency current or voltage. The term dates from the first three decades of radio (1888-1918). Unlike modern radio stations which transmit sound (an audio signal) on an uninterrupted carrier wave, early radio stations transmitted information by ''radiotelegraphy''. The transmitter was switched On-off_keying, on and off to produce long or short periods of radio waves, spelling out text messages in Morse code. Therefore, early radio receiver, radio receivers had only to distinguish between the presence or absence of a radio signal. The device that performed this function in the receiver circuit was called a ''detector''. A variety of different detector devices, such as the coherer, electrolytic detector, magnetic detector and the crystal detector, were used during the wireless telegraphy era until superseded by vacuum tube technology. After sound (amplitude modulation, AM) transmission began ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Interrupter
An interrupter in electrical engineering is a device used to interrupt the flow of a steady direct current for the purpose of converting a steady current into a changing one. Frequently, the interrupter is used in conjunction with an inductor (coil of wire) to produce increased voltages either by a back emf effect or through transformer action. The largest industrial use of the interrupter was in the induction coil, the first transformer, which was used to produce high voltage pulses in scientific experiments and to power arc lamps, spark gap radio transmitters, and the first X-ray tubes, around the turn of the 20th century. Its largest use was the contact breaker or "points" in the distributor of the ignition system of gasoline engines, which served to periodically interrupt the current to the ignition coil producing high voltage pulses which create sparks in the spark plugs. It is still used in this application. Medical use Bird's interrupter The physician Golding Bird desi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Carrier Wave
In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has a much higher frequency than the input signal does. The purpose of the carrier is usually either to transmit the information through space as an electromagnetic wave (as in radio communication), or to allow several carriers at different frequencies to share a common physical transmission medium by frequency division multiplexing (as in a cable television system). The term originated in radio communication, where the carrier wave creates the waves which carry the information (modulation) through the air from the transmitter to the receiver. The term is also used for an unmodulated emission in the absence of any modulating signal. In music production, carrier signals can be controlled by a modulating signal to change the sound property of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Beat Frequency Oscillator
In a radio receiver, a beat frequency oscillator or BFO is a dedicated oscillator used to create an audio frequency signal from Morse code radiotelegraphy ( CW) transmissions to make them audible. The signal from the BFO is mixed with the received signal to create a heterodyne or beat frequency which is heard as a tone in the speaker. BFOs are also used to demodulate single-sideband (SSB) signals, making them intelligible, by essentially restoring the carrier that was suppressed at the transmitter. BFOs are sometimes included in communications receivers designed for short wave listeners; they are almost always found in communication receivers for amateur radio, which often receive CW and SSB signals.Larry Wolfgang, Charles Hutchinson (ed), ''The ARRL Handbook for Radio Amateurs Sixty Eighth Edition'', ARRL, -9, pages 12-29,12-30 The beat frequency oscillator was invented in 1901 by Canadian engineer Reginald Fessenden. What he called the "heterodyne" receiver was the first ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alexander Meissner
Alexander Meissner (in German: Alexander Meißner) (September 14, 1883 – January 3, 1958) was an Austrian engineer and physicist. He was born in Vienna and died in Berlin. His field of interest was: antenna design, amplification and detection advanced the development of radio telegraphy. In March 1913 he discovered the principle of positive feedback independently of Edwin Armstrong, and by applying positive feedback to vacuum tube amplifiers, Meissner co-invented the electronic oscillator,, in German. The patent does not mention Meissner; the patent was issued to the Gesellschaft für Drahtlose Telegraphie mbH (Corporation for Wireless Telegraphy). * See also: Meissner, Alexander."Production of waves by cathode ray tubes"U.S. Patent No. 1,924,796. (filed: 16 March 1914; issued: 29 August 1933). which became the basis of radio transmission by 1920 and has innumerable uses today. The inductively-coupled oscillator circuit he invented is today known as the Meissner oscillator ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electronic Oscillator
An electronic oscillator is an electronic circuit that produces a periodic, oscillation, oscillating electronic signal, often a sine wave or a square wave or a triangle wave. Oscillation, Oscillators convert direct current (DC) from a power supply to an alternating current (AC) signal. They are widely used in many electronic devices ranging from simplest clock generators to digital instruments (like calculators) and complex computers and peripherals etc. Common examples of signals generated by oscillators include signals broadcast by Transmitter, radio and television transmitters, clock signals that regulate computers and quartz clocks, and the sounds produced by electronic beepers and video games. Oscillators are often characterized by the frequency of their output signal: *A Low-frequency oscillation, low-frequency oscillator (LFO) is an electronic oscillator that generates a frequency below approximately 20 Hz. This term is typically used in the field of audio synthesiz ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Reginald Fessenden
Reginald Aubrey Fessenden (October 6, 1866 – July 22, 1932) was a Canadian-born inventor, who did a majority of his work in the United States and also claimed U.S. citizenship through his American-born father. During his life he received hundreds of patents in various fields, most notably ones related to radio and sonar. Fessenden is best known for his pioneering work developing radio technology, including the foundations of amplitude modulation (AM) radio. His achievements included the first transmission of speech by radio (1900), and the first two-way radiotelegraphic communication across the Atlantic Ocean (1906). In 1932 he reported that, in late 1906, he also made the first radio broadcast of entertainment and music, although a lack of verifiable details has led to some doubts about this claim. Early years Reginald Fessenden was born October 6, 1866, in East Bolton, Quebec, the eldest of the Reverend Elisha Joseph Fessenden and Clementina Trenholme's four children. Elisha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modulator
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the ''carrier signal'', with a separate signal called the ''modulation signal'' that typically contains information to be transmitted. For example, the modulation signal might be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal representing a sequence of binary digits, a bitstream from a computer. The carrier is higher in frequency than the modulation signal. In radio communication the modulated carrier is transmitted through space as a radio wave to a radio receiver. Another purpose is to transmit multiple channels of information through a single communication medium, using frequency-division multiplexing (FDM). For example in cable television which uses FDM, many carrier signals, each modulated with a different television channel, are transported through a sing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electromagnet
An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the hole in the center of the coil. The magnetic field disappears when the current is turned off. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet. The main advantage of an electromagnet over a permanent magnet is that the magnetic field can be quickly changed by controlling the amount of electric current in the winding. However, unlike a permanent magnet that needs no power, an electromagnet requires a continuous supply of current to maintain the magnetic field. Electromagnets are widely used as components of other electrical devices, such as motors, generators, electromechanical solen ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Valdemar Poulsen
Valdemar Poulsen (23 November 1869 – 23 July 1942) was a Danish engineer who made significant contributions to early radio technology. He developed a magnetic wire recorder called the telegraphone in 1898 and the first continuous wave radio transmitter, the Poulsen arc transmitter, in 1903, which was used in some of the first broadcasting stations until the early 1920s. Early life Poulsen was born on 23 November 1869 in Copenhagen. He was the son of the Supreme Court judge Jonas Nicolai Johannes Poulsen and Rebekka Magdalene (née Brandt). Recording innovations The magnetic recording was demonstrated in principle as early as 1898 by Poulsen in his telegraphone. Magnetic wire recording, and its successor, magnetic tape recording, involve the use of a magnetizable medium which moves past a recording head. An electrical signal, which is analogous to the sound that is to be recorded, is fed to the recording head, inducing a pattern of magnetization similar to the signal. A p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spark Gap Transmitter
A spark-gap transmitter is an obsolete type of radio transmitter which generates radio waves by means of an electric spark."Radio Transmitters, Early" in Spark-gap transmitters were the first type of radio transmitter, and were the main type used during the wireless telegraphy or "spark" era, the first three decades of radio, from 1887 to the end of World War I. German physicist Heinrich Hertz built the first experimental spark-gap transmitters in 1887, with which he proved the existence of radio waves and studied their properties. A fundamental limitation of spark-gap transmitters is that they generate a series of brief transient pulses of radio waves called damped waves; they are unable to produce the continuous waves used to carry audio (sound) in modern AM or FM radio transmission. So spark-gap transmitters could not transmit audio, and instead transmitted information by radiotelegraphy; the operator switched the transmitter on and off with a telegraph key, creating pulses ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
