BACKGROUND

Radio Waves - Basics

Radio waves contain both electric and magnetic fields, and are a very complex form of energy. Because radio waves contain both electric and magnetic fields, radio waves are also referred to as electromagnetic radiation. These electric and magnetic fields oscillate perpendicular to the direction the waves travel, simultaneously perpendicular to each other. All electromagnetic waves travel with a velocity equal to that of light (3.0 × 10^8 m/s^-1). Radio waves can be measured in frequency and amplitude. Radio waves are used to transport information without the use of wires. Various frequencies of radio waves are used for television, radios, mobile phone, and other communications based on their propagation qualities. Radio waves have the longest wavelengths in the electromagnetic spectrum. Their wavelengths can be as short as a few millimeters or as long as hundreds of miles. Propagation can be described as the movement of a wave through a medium. Although radio waves are used for communications, many things, in nature and others manmade can interfere with radio waves as they are traveling within the Earth’s atmosphere. The atmosphere influences radio waves the way it does because of a lack of the same conditions within and throughout the Earth’s atmosphere. Knowing how the Earth’s atmosphere affects radio waves is very important when dealing with radio propagation. Conditions in the atmosphere vary with changes in height, location, and even the time of the day or year. The sun also affects radio waves as they propagate.

Radio Waves – Application

Radio waves can be applied to the real world in many ways. They can be used to convey information across distances without wired connections. These distances can be relatively small, such as in using a walkie talkie, or very great, such as in communicating with a space vehicle. Radio waves can also be used in locating and measuring devices, such as weather radar (locating rain and other severe weather) and speed measuring radar guns (such as the ones used by law enforcement). Radio waves can even be used in heating devices, such as microwave ovens. In communications, radio waves are encoded with information. Two common types are amplitude modulation or AM and frequency modulation or FM. In amplitude modulation, the strength or amplitude of the wave is varied to encode information. The frequency remains constant. In frequency modulation the frequency of the wave is varied to encode information. The amplitude remains constant. There are many other forms of modulation, or encoding of radio waves, for different applications. Radio waves also have a medical application. It has been discovered that concentrated radio waves can be use to combat abnormal cell growth, such as cancer. Radio waves are also used Magnetic Resonance Imaging (MRI) along with magnetism and a computer.

Sound Waves

Sound is the vibration of molecules that are transferred through a medium, such as a gas, solid, or liquid. This is why there is no sound in space. The sound has no material to travel through. In order for sound to be detected another object must vibrate. When these air molecules push together or vibrate you get what is called a sound wave. Although you hear of air being the most common medium, sound waves will readily travel through water and many other materials that will be tested. Even though sound does travel through some of these materials, sound waves are absorbed by some of these materials also. In fact, some materials prevent the wave from penetrating all together. Sound waves can be more than just absorbed, they can be reflected and refracted (bent) too. When a sound wave is reflected it can result in an echo. This is useful as in medical sonograms, similar to radar, but using sound waves. Sound waves have characteristics such as amplitude, velocity, wavelength, and frequency. Every wave has different characteristics just as a sound wave has its own characteristics. Sound waves travel 1,088 feet per second, but temperature and medium density impact how fast sound travels. For example, sound travels slower when it is cold, but faster when it is hot, due to differences in air density.

Frequency

The frequency of a wave is the rate at which the waves pass a given point. The frequency is also the rate at which the medium vibrates. The pitch is also known as the frequency. Frequency is usually measured in Hertz or Hz. The velocity, wavelength, and frequency are all related because for one, they all are characteristics of radio waves and two, they all are used in this formula: velocity = wavelength x frequency. When you are dealing with the frequency, wavelength, and amplitude, they affect each other. For example, when the wavelength is shorter, the frequency is higher, causing the strength of the wave to be higher. There are many different frequency bands when dealing with radio waves. There is extremely low frequency (ELF), superlow frequency (SLF), ultralow frequency (ULF), very low frequency (VLF), low frequency (LF), medium frequency (MF), high frequency (HF), and so on ending at extremely high frequency (EHF). These different frequency bands are based on the different frequency ranges in Hertz (Hz). In turn, these bands can also be classified by wavelength because of how frequency and wavelength affect each other. Extremely low frequency has a frequency range from 3 Hertz to 30 Hertz and a wavelength range from 100,000 kilometers (km) to 10,000 kilometers. Superlow frequency has a frequency range from 30 Hertz to 300 Hertz and a wavelength range from 10,000 kilometers to 1,000 kilometers. Bands progress from low to high by a multiple of ten. There are a few simple rules to remember when dealing with frequency and radio waves: The lower the frequency, the further the radio wave travels; The lower the frequency, the better the radio wave travels through and around things; The higher the frequency, the more data the radio wave can transport. Higher frequencies can transport more data because the faster the wave swings or beats, the more the wave can carry.

Hertz

Hertz is a unit of frequency measurement. At one time frequency units were expressed in cycles per second or c/s. This unit of measure, cycles per second was redefined as Hertz, in recognition of Heinrich Hertz. Heinrich Hertz is credited with sending and receiving the first radio waves in the mid 1800’s. One cycle per second equals 1 Hertz. Hertz is usually abbreviated as Hz. One thousand Hertz is represented as kilohertz (kHz) and one million Hertz is represented as megahertz (MHz).

Wavelength

Wavelength is the physical distance a wave travels in one cycle (or from one peak to the next). The mathematical relationship between wavelength, wave speed, and frequency is represented by the formula λ = c/f , where λ = wavelength, c = speed of light, and f = frequency in Hertz or Hz. Though the wave speed is influenced by the medium the wave is traveling through, radio wave speed is usually represented by c, the speed of light in a vacuum. (Light is of a shorter wavelength than radio waves.) There are a few simple rules to remember when dealing with wavelength and radio waves: The longer the wavelength, the further the radio wave travels; The longer the wavelength, the better the radio wave travels through and around things; The shorter the wavelength, the more data the radio wave can transport. Longer wavelengths can transport more data because the faster the wave swings or beats, the more the wave can carry.

Amplitude

The amplitude is the height of a wave or the depth of its trough. The amplitude of a wave also represents the wave strength at any particular frequency. Amplitude determines the intensity or brightness of a wave. Radio wave amplitude or strength, of a transmitted and received radio wave, can be affected by many factors. These factors can be environmental, such as blockages or reflectors in the path of the transmitted wave, interference, from other similar radio waves (manmade or natural) or design elements, such as transmitting and receiving antenna efficiency and directivity.

Decibels

Decibels or dB is an expression of the logarithmic ratio of two measurements. Since it expresses a ratio of two quantities with the same unit, it is a dimensionless unit or quantity. A dimensionless quantity is a quantity of measure that does not have any physical units. A decibel is one tenth of a bel (B). In working with radio waves, dB is often used to express the ratio between power levels of two radio waves. The symbol dBm, is a ratio referenced to a standard power level of one milliwatt.

Spectrum Analyzer

A spectrum analyzer is a piece of electronic test equipment that allows the user to view dBm or the decibel output of different frequencies. This is an important tool in measuring waves because the dBm of a wave varies based on the frequency and type of wave. A simple voltmeter does not allow the user to view the wave itself. There are many different settings and parts on a spectrum analyzer. Some of the settings may include dB per division, reference level, center frequency, and many other options to choose from. The different parts may include the display or the frequency selection. A lot of times a spectrum analyzer is used for troubleshooting malfunctioning electronic equipment. A spectrum analyzer is able to do this by presenting a display of the waves at any point within the equipment.

Voltage

Voltage is measured in joules per coulomb, otherwise known as volts, and is the difference of electrical potential between two points of an electrical circuit. Voltage can be measured with a voltmeter, a potentiometer, or an oscilloscope. A volt is a unit of measurement of force, or pressure, in an electrical circuit. The symbol used for volt is V.

Signal Generator

Signal generators are pieces of equipment that are used to generate radio waves. Settings on a signal generator include the frequency of the generated wave and the amplitude of the generated wave. Signal generators also give you the option to use amplitude modulation or frequency modulation.

Transmitters

Transmitters process some sort of signal providing link for the processed radio wave to an antenna. The transmitter converts signals to a specific frequency and, using some type of modulation technique, in parts information to the radio wave.

Receivers

Receivers are an important element in the use of radio waves for communications. Receivers provide the link between an antenna and end use device, such as a speaker for sound or a screen as in a television receiver. Receivers process a radio wave and convert that wave to the desirable usable signal.

Antennas

Antennas are important in working with radio waves, as they are the points at which the waves transition to and from free space. There are many types of antennas, usually selected for their specific properties. Directional antennas are used to focus radio waves (like a flashlight) in a specific direction, such as in a satellite TV antenna. Nondirectional antennas do not focus radio waves and are used where directivity is not desirable, such as in cell phones.

Huygens’s Principle

This principle was proposed by the physicist Christiaan Huygens. This principle of wave analysis basically states that:
Every point on a wave-front may be considered a source of secondary spherical wavelets which spread out in the forward direction at the speed of light. The new wave-front is the tangential surface to all of these secondary wavelets.
This means that each point of an advancing wave front is the center of a fresh disturbance and the source of a new train of waves. This view of wave propagation helps better understand a variety of wave phenomena, such as diffraction.

Fourier Series

The Fourier Transform operates by analyzing an input waveform into a series of sinusoidal waves of various frequencies and amplitudes. This is called a Fourier Series. Any waveform can be built from only sine and cosine waves of various amplitudes, and therefore any waveform can be broken down or analyzed into these same components. The classic example of sine wave synthesis is a square wave, built from a sine wave at the fundamental frequency, plus another at 3 times that frequency, but 1/3 the amplitude, plus a 5th harmonic at 1/5 the amplitude, and so on for all odd harmonics.

History

Radio waves are as old as the universe. Natural radio waves are generated by many types of large disturbances, such as lightning. Stars and the sun emit radio waves as a by-product of their ongoing reactions. Manmade radio waves are a much more recent invention. The first manmade radio wave transmission and reception occurred in the mid 1800’s. In 1856, James Clark Maxwell proposed that light and other forms of radiant energy propagate themselves in the form of waves, through space. Only in the early 1920’s did radio wave use become widespread, with the inception of the first radio broadcast stations. Today, radio waves are used in many applications for communications, medical, military, and other fields. As technology has progressed it is now possible to package sophisticated radio transmitters and receivers, in very small packages, as in the typical cell phone.

Wave Interaction

When waves interact, they superimpose on each other, and the amplitude at any point of interaction is the sum of the amplitudes of the two individual waves. This is not true for the other properties of waves. To explain, the frequency of the resultant wave will remain the same as the frequency of the two input waves. This only true if the two input waves have the same frequency. The phase of a resultant wave is the average of the two input waves. Wave interaction can be used to form or create other types of waveforms. Every type of waveform can be created through the interaction of multiple sine waves. For example, a square wave can be created by mixing a number of different sine waves.