Radiowaves

Radio waves/Electromagnetic Radiation. A fundamental force of nature that has shaped the world we live in today. From the radio waves that carry our communications to the light that allows us to see, electromagnetic radiation has always played a role in our daily lives.
But its impact extends far beyond our personal experiences. Electromagnetic radiation has played a pivotal role in shaping geopolitics, from the development of radar during World War II to the use of satellite imagery for intelligence gathering. Undoubtedly, the applications of electromagnetic radiation has played a pivotal role in shaping our modern life.

History

In the 19th century, Michael Faraday discovered that electric currents could produce magnetic fields. Building on this foundation, James Clerk Maxwell mathematically proved Faradays discoveries in 1864 that any oscillating electrical disturbance could have an effect at a considerable distance from its source at the speed of light. This disruption took the form of waves traveling outward from a source, such as a charged electron, propagating through space. This was a pivotal moment in the development of radio technology. During his trials, he also predicted the existence of electromagnetic waves.

Heinrich Hertz

Later in Germany, Heinrich Hertz created a spark-gap transmitter. The experiment was conducted by: two hollow zinc spheres with a diameter of 30cm and a distance of 3 meters between them. These two zinc spheres act as capacitors. 2mm thick copper wire is run from each end of the spheres to the middle with a small gap between each wire. This gap is where a spark will form from the voltage applied to the antenna.

High voltage is applied to this antenna, and the wave generated by this antenna is sent through the air into the receiving end of the antenna parallel to the transmitter. The wave propagating through the air hits the receiving antenna, producing an electric current over the air. The electromagnetic waves from the transmitter generate electrical vibrations in the receiver, causing sparks between the two ends of the transmitting antenna.
This experiment did not prove to be monumental to Hertz, saying it would not “have any practical application.” Even so, in 1901, this design would lead to the first wireless transmission across the Atlantic Ocean from Britain to Canada. Marconi, the lead of this experiment, held a kite to raise a wire acting as an antenna. This antenna detected a signal transmitted from Poldhu, Cornwall, England. This long-range transmission is possible because the radio waves propagated through the atmosphere, reflecting off land, water, and the ionosphere.

But, the idea of waves propagating through space was not new. Light had already been widely understood as a wave. Conducted in 1801, Thomas Young performed a double-slit experiment. Two slits placed a distance apart allowed light to travel through them. Interference patterns appeared in the light that was delivered via these perforations. This experiment showed that matter and light can exhibit traits of both classically defined waves and particles, and it also showed that quantum mechanical events are fundamentally probabilistic. The quantum mechanics of this is not important though.

Phenomenon

Before explaining the topic of radio waves, it is important to understand the broader topic of electromagnetic radiation.
Electromagnetic radiation is produced when a charged particle, such as an electron or proton, changes its position. The displacement affects the charged particles’ electromagnetic field, as Micheal Faraday discovered in 1831. James Clerk Maxwell also found that a changing electromagnetic field generates a changing magnetic field.
The change in electromagnetic and magnetic fields is what carries energy through space. When a charged particle is oscillated, its movement can be represented as a sine wave. The faster the electron moves, the greater the energy it contains and emits as electromagnetic radiation. The wavelength of an electromagnetic wave is inversely proportional to its frequency, meaning waves with higher frequencies have shorter wavelengths and vice versa.
When an electromagnetic is generated, it self-propagates throughout space because of a time-varying magnetic field that produces a time-varying electric field and vice versa. This is referred to as a wave train.

Properties

Radio waves can be scattered, reflected, and refracted. In this section, electromagnetic radiation and radio waves will be used interchangeably because radio waves follow all of the rules of electromagnetic radiation.
As with all waves, radio waves can be superposed. This superposition is why you can hear static in radios. It is because of waves interfering with each other in space.

When an electromagnetic wave interacts with a charged particle, the particle experiences a force proportional to the magnitude of the electric field. This force causes the particle to change its motion and oscillate with the same frequency as the incoming electric field of the wave. As a result, the charged particle becomes a new source of electromagnetic radiation, resonating at the same frequency as the original wave. According to the laws of conservation of energy, energy is conserved in this system, it is transferred from one particle to another. The transmitting wave loses energy as it causes the charged particles to resonate with its frequency, while the charged particles gain energy and emit electromagnetic radiation.
On this principle, radio waves can penetrate non-conductive materials, such as rock, with minimal energy loss because non-conductive materials do not contain free electrons that can absorb the energy of the radio waves. However, when radio waves pass through conductive materials, such as metal or water, the charged particles within the material can resonate with the frequency of the transmitted wave. This resonance removes energy from the transmitted wave, weakening the signal.

Detachment

All electromagnetic waves travel at the speed of light. A particle moving throughout space generates an electric field. This varying electric field generates a wave. The wave propagates through space because of the directional vector that carries information on the magnitude and direction of the flow of energy, a Poynting vector. This is the chain effect of an electric field generating a magnetic field and vice versa.

Applications

There are many careers related to the knowledge of radio waves.

Radar

Developmental work on the radar utilizing radio waves started in 1930, with tensions in Europe rising. In 1904, a patent for an obstacle detector and ship navigation device based on the principles of wireless transmission as demonstrated by Hertz. Using a transmitter, the radar emits lower-frequency radio waves or higher-frequency microwaves and detects disturbances in the transmitted wave. Disturbances are seen when the transmitted wave is reflected back to the radar, where it can be used to determine the speed and location of the object.

Television and Audio

Transmitting television signals over radio waves is similar to transmitting audio signals over radio waves, as both use the same principles of transmission. A carrier wave, which is a radio wave that resonates at a specific frequency, transmits information through the air. Video and audio signals can be added to the carrier wave through a process called modulation. One example of modulation is amplitude modulation (AM), where the amplitude of the carrier wave is varied in accordance with the amplitude of the injected signal. This allows the information contained in the video or audio signal to be transmitted along with the carrier wave.

Below is a circuit to demonstrate Amplitude Modulation of a video signal over the air.

Each repsective potentiometer in the circuit is responsible for controlling the brightness and contrast of the image.
Realistically, this is not the case, and they are used to slightly offset the voltage and frequency of each harmonic.

The following table is taken from Wikipedia:
Television channel frequencies. (2023, June 14). Retrieved June 15, 2023, from Wikipedia: Television channel frequencies

Channel	Lower edge	ATSC 1 pilot	Video carrier	ISDB-T/Tb center	Audio carrier	Upper edge
1	44	44.31	45.25	47.142857	49.75	50
2	54	54.31	55.25	57.142857	59.75	60
3	60	60.31	61.25	63.142857	65.75	66
4	66	66.31	67.25	69.142857	71.75	72
5	76	76.31	77.25	79.142857	81.75	82
6	82	82.31	83.25	85.142857	87.75	88

I cannot validate any of the columns other than “Channel,” “Lower edge,” “Video carrier,” and “Upper edge.” But from my testing, the 12MHz crystal, when resonating at its 7th harmonic (12MHz * 7 = 84MHz), falls just over the “Video carrier” frequency in Channel 6, making it easier for my TV to tune to the frequency of 84MHz. The crystal can resonate on its 5th harmonic, broadcasting on Channel 3, but I found the signal in my testing unreliable. Unfortunately, tuning into such a high harmonic frequency made the signal weaker across longer distances because of the reduced Voltage. Remember that Amplitude represents the maximum field strength of the electric and magnetic fields propagating through the wave.

Careers

There are many careers related to the knowledge of radio waves.

Radio Frequency Engineering

Radio Frequency Engineers specialize in designing, developing, and manufacturing electrical equipment and software for devices that use radio waves. Phones, cellular towers, Wi-Fi-enabled devices, and radios all have to do with radio frequency engineering.
Radio Frequency Engineers use engineering and computer knowledge to program and create devices for radio communications. They may also do extensive fieldwork to determine precisely where equipment should be placed and how it should be set up for optimal use. A bachelor’s degree in engineering or a related field like a computer or electrical engineering is needed to become a radio frequency engineer.

Meteorological Science

Experts in meteorological science use radio waves to observe and forecast weather conditions. For example, a Doppler radar is a tool that uses radio waves to provide information about precipitation and storms.
A deep understanding of the properties of radio waves is essential to make accurate predictions about weather conditions. Usually, a bachelor’s degree in atmospheric science is needed.

Contributions

Reginald Fessenden – Canadian

Reginald Fessenden, born on the 6th of October 1866 in “Canada East,” present day Quebec is seen as a pioneer in radio communication.
Fessenden was the first to make a voice transmission over radio waves and laid out the foundations of Amplitude Modulation by inventing and patenting components used in wireless transmission of voice over radio. Fessenden created the superheterodyne principle. A principle used in electronic oscillators to shift signals between frequency ranges. It is also used in modulating and demodulating signals transmitted over the air.

Heinrich Hertz

Heinrich Hertz, born on the 22nd of February 1857 in Germany, was the first to observe electromagnetic radiation. In 1887, Hertz conducted an experiment of transmitting radio waves induced by current over the air. This experiment mentioned earlier in History was the first discovery of radio waves.

James Clerk Maxwell

Born in 1831 in Scotland, Maxwell revolutionized the understanding of electromagnetic radiation. As electromagnetic waves were a new principle at the time, the ideas of electromagnetic radiation were not coherent. Maxwell took the ideas of Micheal Faraday and set to work trying to represent his ideas in mathematical form. Maxwell derived the following equations.

The equations presented mathematically describe how electric and magnetic charges, currents, and field changes generate fields. These equations can also demonstrate how fluctuations in electromagnetic fields propagate at a constant speed in a vacuum. Maxwell originated the idea of electromagnetic radiation from his field equations.

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