2.3-Development-of-Radio-Transmitter.pdf
- 2. The first primitive radio transmitters (called spark gap transmitters) were built by German physicist Heinrich Hertz in 1887 during his pioneering investigations of radio waves.
- 3. These generated radio waves by a high voltage spark between two conductors. Hertz discovering radio waves in 1887 with his first primitive radio transmitter (background).
- 4. Beginning in 1895, Guglielmo Marconi developed the first practical radio communication systems using these transmitters, and radio began to be used commercially around 1900.
- 5. These spark-gap transmitters were used during the first three decades of radio (1887- 1917), called the wireless telegraphy or "spark" era.
- 6. Low-power inductively coupled spark-gap transmitter on display in Electric Museum, Frastanz, Austria. The spark gap is inside the box with the transparent cover at top center. Guglielmo Marconi's spark gap transmitter, with which he performed the first experiments in practical radio communication in 1895-1897
- 7. Because they generated damped waves, spark transmitters were electrically "noisy". Their energy was spread over a broad band of frequencies, creating radio noise which interfered with other transmitters.
- 8. Damped wave emissions were banned by international law in 1934. Two short-lived competing transmitter technologies came into use after the turn of the century, which were the first continuous wave transmitters:
- 9. the arc converter (Poulsen arc) in 1904 and the Alexanderson alternator around 1910, which were used into the 1920’s.
- 10. 1 MW US Navy Poulsen arc transmitter which generated continuous waves using an electric arc in a magnetic field, a technology used for a brief period from 1903 until vacuum tubes took over in the 20’s.
- 11. An Alexanderson alternator, a huge rotating machine used as a radio transmitter at very low frequency from about 1910 until World War 2.
- 12. All these early technologies were replaced by vacuum tube transmitters in the 1920s, which used the feedback oscillator invented by Edwin Armstrong and Alexander Meissner around 1912, based on the Audion (triode) vacuum tube invented by Lee De Forest in 1906.
- 13. Vacuum tube transmitters were inexpensive and produced continuous waves, and could be easily modulated to transmit audio (sound) using amplitude modulation (AM).
- 14. One of the first vacuum tube AM radio transmitters, built by Lee De Forest in 1914. The early Audion (triode) tube is visible at right.
- 15. This made AM radio broadcasting possible, which began in about 1920. Practical frequency modulation (FM) transmission was invented by Edwin Armstrong in 1933, who showed that it was less vulnerable to noise and static than AM.
- 16. The first FM radio station was licensed in 1937. Experimental television transmission had been conducted by radio stations since the late 1920s, but practical television broadcasting didn't begin until the late 1930s.
- 17. One of the BBC’s first broadcast transmitters, early 1920’s, London. The 4 triode tubes, connected in parallel to form an oscillator, each produced around 4 kilowatts with 12 thousand volts on their anodes.
- 18. The development of radar during World War II motivated the evolution of high frequency transmitters in the UHF and microwave ranges, using new active devices such as the magnetron, klystron, and traveling wave tube.
- 19. The invention of the transistor allowed the development in the 1960s of small portable transmitters such as wireless microphones, garage door openers and walkie- talkies.
- 20. The development of the integrated circuit (IC) in the 1970s made possible the current proliferation of wireless devices, such as cell phones and Wi-Fi networks, in which integrated digital transmitters…
- 21. … and receivers (wireless modems) in portable devices operate automatically, in the background, to exchange data with wireless networks.
- 22. The need to conserve bandwidth in the increasingly congested radio spectrum is driving the development of new types of transmitters such as spread spectrum, trunked radio systems and cognitive radio.
- 23. A related trend has been an ongoing transition from analog to digital radio transmission methods.
- 24. Digital modulation can have greater spectral efficiency than analog modulation; that is, it can often transmit more information (data rate) in a given bandwidth than analog, using data compression algorithms.
- 25. Other advantages of digital transmission are increased noise immunity, and greater flexibility and processing power of digital signal processing integrated circuits.
- 26. Armstrong's first experimental FM broadcast transmitter W2XDG, in the Empire State Building, New York City, used for secret tests 1934–1935. It transmitted on 41 MHz at a power of 2 kW.
- 27. Transmitter assembly of a 20 kW, 9.375 GHz air traffic control radar, 1947. The magnetron tube mounted between two magnets (right) produces microwaves which pass from the aperture (left) into a waveguide which conducts them to the dish antenna.
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