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What do Radio Waves and Microwaves Have in Common?
Radio waves and microwaves are bands of energy spanning a range of wavelengths within the electromagnetic spectrum. They are a form of radiation.
Most people have a very negative view of radiation, but we will discuss that below.
Radio waves and microwaves both are used for communication and microwaves are actually considered a subset of radio wave transmissions. Radio waves are specifically used for fixed transmission and mobile communication in AM, FM, television, and microwave frequencies.
Microwave frequencies, which are shorter than most of the radio band, are on one end of the radio frequency spectrum.
Electromagnetic waveforms are described by several characteristics. Waves have amplitude (energy intensity measured in Watts, typically graphed as the height of a wave peak), frequency (how often a pulse of energy is transmitted measured in cycles/second or Hertz, graphed as a wave), and wavelength (distance between pulses of energy measured in meters, graphed as a distance between waves).
What are radio waves??
AM Radio waves (540-1600 kHz) are amplitude modulated, meaning that the transmitter sends out a series of differing intensity pulses in a pattern on top of a fixed radio transmission wave (the carrier wave, corresponding to the frequency of the radio station). These pulse patterns relate to information, such as audio recording.
A receiver built to interpret and convert these signals transduces the pulse patterns back into an audio signal and transmits it to a speaker so that it can be heard.
FM Radio waves (88-108 MHz) are frequency modulated, meaning that the transmitter sends out pulses of energy at constant amplitude on top of a fixed carrier wave, but at different rates (frequencies). These differing compressions of energy are usually audio signals that have been converted.
A receiving station is able to back-convert these intermittent pulses of energy pattern to the original audio signal and send them out to a speaker to be heard.
Television waves send much more complex waveforms due to the audio and visual data being transmitted. They come in two transmission bands: Very High Frequency (VHF) which uses two bandwidths (54-88 MHz and 174-222 MHz, bracketing the radio audio FM band) and Ultra High Frequency (UHF) which uses 470-1000 MHz transmission.
VHF transmissions send video over AM radio bands and audio over FM radio bands.
Microwaves are transmissions in the 300 MHz to 300 GHz band, with wavelengths from one meter down to one millimeter in length. Apart from communication uses, they are also used for navigation (GPS), radar, in radio astronomy, heating (microwave ovens), power transmission, and spectroscopy.
There is a total of 13 registered, application-specific microwave bands; only 12 of them are currently used.
Different electromagnetic waves have different transmission characteristics and are used in various applications to get around obstacles. For example, long waves tend to go around obstacles (diffract) such as mountains and follow the electromagnetic field lines of the earth.
Short waves bounce off the ionosphere, a charged region of the upper atmosphere, and go over the horizon for greater distance transmissions. Very short waves (e.g., microwaves) are line-of-sight only, however there are transmission techniques that can be applied to increase transmission distance, such as tropospheric scatter.
This latter method of transmission requires a receiver, usually over the horizon, that can reconstruct microwave signals that become randomly scattered in the troposphere layer of the atmosphere. This method permits microwave transmissions at distances up to 300 km.
Reception of electromagnetic signals involves use of an omnidirectional antenna, a dipole antenna, or a parabolic dish depending on the signal band received. Signal communications in short wavelengths are very amenable to reception by omnidirectional antennas (think of your typical rabbit-ear antenna or those found on portable radios).
Omnidirectional antennas are also found in microelectronic devices such as cell phones, tablets, laptops, and hand-held GPS receivers. Parabolic dish or other designs (e.g., horn antennas) are used for point-to-point microwave communications (think of a satellite dish).
What is electromagnetic radiation?
Electromagnetic radiation (EMR) is energy transmitted over distance across a broad range of frequencies, ranging from extremely low frequency waves (a type of radio wave starting a 3 Hz) to gamma rays (the shortest EMR wavelength topping at 1.24 x 1020 Hz), with the visual band in between. This also includes heat, which is infrared radiation.
It consists of photons, which are waves of energy that become particles when observed. At the short end of the spectrum, gamma rays always remain waves.
When most people think of radiation, what they usually think of is ionizing radiation, not light coming from a flashlight. Ionizing radiation is in the short end of the electromagnetic spectrum and consists of ultraviolet, x-rays, and gamma rays, things that can burn or cause cancer from differing times of exposure.
Radio waves and microwaves are at the other end of the spectrum. You can think of all electromagnetic radiation (in descending wavelengths), from Extremely Low Frequency (ELF) to Ultra High Frequency (UHF) radio waves, microwaves, infrared light, visible light, X-rays, and gamma rays. They are all essentially light.
Whether radiation is harmful or not is a matter of frequency and energy level (intensity). Extremely intense visible light can burn. Extremely low intensity infrared light will not transmit heat. Just like chemicals, it’s all about dose.
Are radio waves and microwaves safe?
The answer to that question involves energy levels. The only difference between a radio wave and a microwave is frequency.
They are made of the same essential stuff: photons. Most radio wave transmissions are not of sufficient intensity to be dangerous.
However, some radio wave sources are quite intense and can cause soft tissue damage. Standing next to the source of a high-power radio transmitter while it is on would be an extremely bad thing to do.
Soft tissues absorb radio frequencies and convert them to infrared, which causes heating and burns. Most people, though, are not climbing live radio towers and sticking their faces on the transmitter.
Microwaves are a different matter entirely. Microwaves are typically emitted as high-energy bursts and do not have demonstrable biological effects at most emission frequencies.
It has been noted that standing in the directed beam of a microwave emitter can cause neurological effects, producing phantom clicking and popping sounds. This effect is produced by dielectric heating effects on the auditory cortex.
Intense exposure to microwave radiation, from standing in front of a live emitter for example, can result in denaturation of the collagen polymers in the cornea, thus producing cataracts. Exposure to higher energies, such as a broken microwave oven that operates with the door open, can cause soft tissue burns.