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# Electromagnetic Spectrum and Radio Propagation

[Vienna, Austria - Civil Engineering Discoveries]

### -  Electromagnetic Theory

Electricity and magnetism were once thought to be separate forces. However, in 1873, Scottish physicist James Clerk Maxwell developed a unified theory of electromagnetism. The study of electromagnetism deals with how electrically charged particles interact with each other and with magnetic fields.

There are four main electromagnetic interactions:

• The force of attraction or repulsion between electric charges is inversely proportional to the square of the distance between them.
• Magnetic poles come in pairs that attract and repel each other, much as electric charges do.
• An electric current in a wire produces a magnetic field whose direction depends on the direction of the current.
• A moving electric field produces a magnetic field, and vice versa.

Maxwell also developed a set of formulas, called Maxwell's equations, to describe these phenomena.

### - Radio Waves and Electromagnetic Spectrum

Radio spectrum is the part of the electromagnetic spectrum ranging from 1 Hz to 3000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, have become widely used in modern technology, particularly in telecommunication.

Radio waves are measured by wavelength or frequency, with wavelength being the distance between two identical points in a waveform signal, and frequency referring to the number of waves that passes a given point per second. The sweet spot for most modern data communication is between 300 megahertz (MHz) and 6 gigahertz (GHz) frequency.

Most IoT systems link networks of sensors via radio waves, which transmit data from one place to another. Radio waves, which are primarily used in communication technologies, are a type of electromagnetic radiation (a form of energy); they make up a small part of what is called the electromagnetic (EM) spectrum, which is divided up into sections called frequency bands.

The EM spectrum is a limited resource - there are only so many radio frequencies in existence. But too much activity on particular radio frequency bands would create interference to the point where nothing would be discernible. Like other countries, the U.S. has tasked a government organization, the Federal Communications Commission (FCC), to allocate the spectrum so it’s used effectively.

### - Wireless Signals

Wireless signals are important because they can transfer information - audio, video, our voices, data - without the use of wires, and that makes them very useful. Wireless signals are electromagnetic (EM) waves travelling through the air.

Electromagnetic (EM) radiation is a form of energy that is all around us and takes many forms, such as radio waves, microwaves, X-rays and gamma rays. Sunlight is also a form of EM energy, but visible light is only a small portion of the EM spectrum, which contains a broad range of electromagnetic wavelengths.

Signal processing is a subfield of mathematics, information and electrical engineering that concerns the analysis, synthesis, and modification of signals, which are broadly defined as functions conveying "information about the behavior or attributes of some phenomenon", such as sound, images, and biological measurements. For example, signal processing techniques are used to improve signal transmission fidelity, storage efficiency, and subjective quality, and to emphasize or detect components of interest in a measured signal.

### - Electromagnetic Spectrum

Electromagnetic energy travels in waves and spans a broad spectrum from very long radio waves to very short gamma rays. The human eye can only detect only a small portion of this spectrum called visible light. A radio detects a different portion of the spectrum, and an x-ray machine uses yet another portion. All together, electromagnetic waves make up what is called the electromagnetic spectrum. Radio waves are used for wireless transmission of sound messages, or for passing information.

Electromagnetic radiation travels in waves that "vibrate" at different frequencies. Radio waves are in the range of about 10 kHz (or ten thousand waves per second) to 100 GHz (which is one hundred million vibrations per second). Electromagnetic radiation is used for communications and transmission of information. The waves that are used in this way are radio waves, microwaves, infrared radiation and light. Radio waves - are used to transmit television and radio programs. Microwaves - are used to transmit satellite television and for mobile phones. Infrared - is used to transmit information from remote controls.

### - Wave Communication

Today we use codes to send signals using electromagnetic radiation. There are two types of signal, analogue and digital. An analogue signal changes in frequency and amplitude all the time in a way that matches the changes in the voice or music being transmitted. A digital signal has just two values – which we can represent as 0 and 1. An analogue signal varies in frequency and amplitude. A digital signal has two values, 0 and 1 (or ‘on’ and ‘off’).

The signal (voice, music or data) is converted into a code using only the values 0 and 1. The signal becomes a stream of 0 and 1 values. These pulses are added to the electromagnetic wave and transmitted. The signal is received and then decoded to recover the original signal. Both analogue and digital signals can pick up unwanted signals that distort the original signal. These unwanted signals are called noise. Digital signals can be cleaned up in a process known as regeneration because each pulse must be a 0 or a 1, so other values can be removed. Analogue signals can be amplified, but the noise is amplified too. This is why digital signals give a better-quality reception.
Digital signals give a better-quality reception because noise on digital signals is more easily removed.

### - Demand For Spectrum Is Exploding

Spectrum = electromagnetic energy. It is all around us. Radio spectrum is broken up into what we call frequency “bands” (distinct parts of spectrum based on how often their energy waves oscillate) to transmit and receive signals. A familiar example may be FM radio. That band, as the numbers on the dial will indicate, goes from 88 megahertz to 108 megahertz - a slice of this large range of spectrum is available for transmitting information.