Day 252~366

The early history of radio is the history of technology that produce and use radio instruments that use radio waves. Within the timeline of radio, many people contributed theory and inventions in what became radio. Radio development began as “wireless telegraphy”. Later radio history increasingly involves matters of broadcasting.
The hertz (symbol Hz) is the unit of frequency in the International System of Units (SI) and is defined as one cycle per second. It is named for Heinrich Rudolf Hertz, the first person to provide conclusive proof of the existence of electromagnetic waves.
Some of the unit’s most common uses are in the description of sine waves and musical tones, particularly those used in radio- and audio-related applications. It is also used to describe the speeds at which computers and other electronics are driven.
In radio, longwave (or long wave) refers to parts of the radio spectrum that has longer wavelengths. These are typically kilometer-sized or greater. The term is a historic one dating from the early 20th century.
Amplitude Modulation, usually shortened to AM, is a simple way to send a radio signal. The signal can travel long distances, and appear in faraway places, because of the earth’s ionosphere. AM signals are mostly sent out on medium wave and shortwave frequencies. They do not carry high fidelity sound, but the sound is good enough to hear most things. Analog signals can fade in and out, or have interference from power lines and power stations. Sunspot activity can also weaken signals.
In telecommunications and signal processing, Frequency Modulation transmits information over a carrier wave by varying the frequency. This technique is different from amplitude modulation which varies the amplitude, but keeps the frequency constant. This kind of modulation is used in broadcasting and other radio work.
In the context of broadcasting, Frequency modulation is often shortened to FM. When transmitting analogue sound, the sound quality of FM signals is better than that of amplitude modulation (AM) signals. However, FM signals do not travel as far as AM.
Many radio stations send out both kinds of signals. AM may be used for talk shows, and FM for music. FM broadcasting usually includes a difference signal, which can cause two different speakers at home to create different sounds. This creates stereo sound.

It still works 🙂


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