KDKA-Pittsburgh broadcasted the Harding-Cox election returns and began a daily schedule of radio programs. In 1927, commercial radiotelephony service linking North America and Europe was opened. In 1935, the first telephone call was made around the world using a combination of wire and radio circuits.

Edwin Howard Armstrong invented frequency-modulated or FM radio in 1933. FM improved the audio signal of radio by controlling the noise static caused by electrical equipment and the earth's atmosphere. Until 1936, all American transatlantic telephone communication had to be routed through England. That year, a direct radiotelephone circuit was opened to Paris.

In 1965, the first Master FM Antenna system in the world, designed to allow individual FM stations to broadcast simultaneously from one source, was erected on the Empire State Building in New York City.

Vocabulary:

dot-dash message (Morse code) – точка-тире сообщение (код Морзе) spark-gap machines – искровые разрядники

ship-to-shore and ship-to-ship communication – связь "корабль-берег" и "корабль-

судно"

be apprehended – быть задержанным triode amplifier – триодный усилитель

amplifying vacuum tube – усилительная вакуумная трубка hamper – мешать, тормозить, затруднять

amplitude-modulated (AM) radio – амплитудно-модулированное (АМ) радио spark-gap transmitters – датчики искрового промежутка frequency-modulated (FM) radio – частотно-модулированное (FM) радио space telegraphy – космическая телеграфия

Radio Waves

Humans perceive the universe using visible light that we can see with our eyes. Yet, there's more to the cosmos than what we see using the visible light that streams from stars, planets, nebulae, and galaxies. These objects and events in the universe also give off other forms of radiation, including radio emissions. Those natural signals fill in an important part of the cosmic of how and why objects in the universe behave as they do.

Radio Waves in Astronomy

Radio waves are electromagnetic waves (light), but we can't see them. They have wavelengths between 1 millimeter (one-thousandth of a meter) and 100 kilometers (one kilometer is equal to one thousand meters). In terms of frequency, this is equivalent to 300 Gigahertz (one Gigahertz is equal to one billion Hertz) and 3 kilohertz. A Hertz (abbreviated as Hz) is a commonly used unit of frequency measurement. One

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Hertz is equal to one cycle of frequency. So, a 1-Hz signal is one cycle per second. Most cosmic objects emit signals at hundreds to billions of cycles per second.

People often confuse "radio" emissions with something that people can hear. That's largely because we use radios for communication and entertainment. But, humans do not "hear" radio frequencies from cosmic objects. Our ears can sense frequencies from 20 Hz to 16,000 Hz (16 KHz). Most cosmic objects emit at Megahertz frequencies, which is much higher than the ear hears. This is why radio astronomy (along with x-ray, ultraviolet, and infrared) is often thought to reveal an "invisible" universe that we can neither see nor hear.

Sources of Radio Waves in the Universe

Radio waves usually are emitted by energetic objects and activities in the universe. The Sun is the closest source of radio emissions beyond Earth. Jupiter also emits radio waves, as do events occurring at Saturn.

One of the most powerful sources of radio emission outside of the solar system, and beyond the Milky Way galaxy, comes from active galaxies (AGN). These dynamic objects are powered by supermassive black holes at their cores. Additionally, these black hole engines will create massive jets of material that glow brightly with radio emissions. These can often outshine the entire galaxy in radio frequencies.

Pulsars, or rotating neutron stars, are also strong sources of radio waves. These strong, compact objects are created when massive stars die as supernovae. They're second only to black holes in terms of ultimate density. With powerful magnetic fields and fast rotation rates, these objects emit a broad spectrum of radiation, and they are particularly "bright" in radio. Like supermassive black holes, powerful radio jets are created, emanating from the magnetic poles or the spinning neutron star. Many pulsars are referred to as "radio pulsars" because of their strong radio emission. In fact, data from the Fermi Gamma-ray Space Telescope showed evidence of a new breed of pulsars that appears strongest in gamma-rays instead of the more common radio. The process of their creation remains the same, but their emissions tell us more about the energy involved in each type of object.

Supernova remnants themselves can be particularly strong emitters of radio waves. The Crab Nebula is famous for its radio signals that alerted astronomer Jocelyn Bell to its existence.

Radio Astronomy

Radio astronomy is the study of objects and processes in space that emit radio frequencies. Every source detected to date is a naturally occurring one. The emissions are picked up here on Earth by radio telescopes. These are large instruments, as it is necessary for the detector area to be larger than the detectable wavelengths. Since radio waves can be larger than a meter (sometimes much larger), the scopes are typically in excess of several meters (sometimes 30 feet across or more). Some wavelengths can be as large as a mountain, and so astronomers have built extended arrays of radio telescopes.

The larger the collection area is, compared to the wave size, the better the angular resolution a radio telescope has. (Angular resolution is a measure of how close two small objects can be before they are indistinguishable.)

Radio Interferometry

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