When people think of ‘radio’, the first thing that comes to mind is the the radio that’s in their car, FM stations with music DJ’s or NPR and AM talk radio or religious programming. And while all of that is radio, it’s not even 1% of what radio is currently in use for in our society.
Radio is used just about everywhere nowadays. Your cell phone has transmitter and antenna array that can both receive and transmit Near Field Communications (NCF payments, 13.56 MHz), Bluetooth (2.45 GHz), WiFi (2.4 GHz and 5 GHz), GSM Cell network (often 698-806 MHz), and 5G cell data network (which has thin slices of bands from 400Mhz all the way to 88Ghz). And that’s just radio signals from a single smartphone. We haven’t even mentioned your phones GPS, your car’s key fob, tire pressure sensors, your house’s Smart Gas and Electric Meter, security cameras, or the utilities SCADA data collection systems, and of course the kids walkie-talkies.
But before we get into that, let’s learn what all those numbers mean after the familiar names of radio communications protocols that everyone uses.
Radio is the lowest frequency, least energetic part of the ElectroMagnetic (EM) Spectrum. This means radio waves have the longest wavelengths (up to 100 kilometers) and the lowest frequencies (down to 3 kilohertz). This also means it takes very little energy to produce radio waves, and in fact are created accidentally by many things, including sparks.
The image to the right shows the entire EM spectrum and the relative sizes of the waves each part uses. We traditionally break up the spectrum into 7 parts. The common names we give them are radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays and gamma-rays.
You can see that three things are physically related here: Frequency of the waves, the length of the waves, and the amount of energy those waves have.
When talking about the radio part of the EM spectrum, we often talk about frequency. The radio region of the EM spectrum goes from 3,000 to 3,000,000,000 times a second, or from 3 kHz to 3 Ghz. Microwave go up to 30 Ghz, followed by infrared at 3 × 1013 Hz. At that point, scientists often switch to talking about wavelength, with red being 700 nanometers (nm) and blue being 400nm. Ultraviolet is next at 100 nm, then X-rays from 10 nm to 1nm. Smaller and higher energy than that is Gamma rays, given off when stars go nova.
Yes, stars. All of these waves we have been talking about are just photons. The very same photons that let you see the words on this webpage. Their differing frequency changes their characteristics. We know from experience that window glass is transparent to visible light, and our muscle and skin is transparent in X-rays taken at the doctors office. So, too, are radio waves transparent to many more things, allowing you to get a signal deep in a building. You can also reflect then as if from a mirror, bouncing off things the ground, the ionosphere, or large buildings. Finally, we can capture some of that energy in an antenna to a receiver that amplifies the signal into something a human could sense, giving that receiver a larger ‘eye’ to collect photons.
Radio is also very low energy compared to the rest of the EM spectrum, allowing a relatively low amount of energy to transmit a useful signal further than you could see a search light of the same energy. This is two of the main reasons radio was discovered quickly during the enlightenment, used often by engineers, and enhancing the functionality of millions of devices.
Since the radio spectrum is so large, covering billions of different frequencies, we often talk about subsections of the radio spectrum that we call bands.
You might recognize some of these bands from their initialism that got used in relation to broadcast television, and the yagi antennas people had on their roofs to get better reception. That same UHF/VHF spectrum is now used by recent cell phones, and TV is broadcast digitally on a higher frequency.
For a much more detailed chart of the radio spectrum and its legal uses, see here: United States Frequency Allocation of the Radio Spectrum Chart. That chart lists 30 different radio services, including aeronautical, marine, satellite, radio astronomy, RADAR, and of course amateur.
| Band | Initials | Frequency range | Wavelength range |
|---|---|---|---|
| Extremely Low Frequency | ELF | <3 kHz | >100 km |
| Very Low Frequency | VLF | 3 to 30 kHz | 10 to 100 km |
| Low Frequency | LF | 30 to 300 kHz | 1 m to 10 km |
| Medium Frequency | MF | 300 kHz to 3 Mhz | 100 m to 1 km |
| High Frequency | HF | 3 to 30 Mhz | 10 to 100 m |
| Very High Frequency | VHF | 30 to 300 Mhz | 1 to 10 m |
| Ultra High Frequency | UHF | 300 Mhz to 3 Ghz | 10 cm to 1 m |
| Super High Frequency | SHF | 3 to 30 Ghz | 1 to 1 cm |
| Extremely High Frequency | EHF | 30 to 300 Ghz | 1 mm to 1 cm |
So to recap, photons of various wavelengths have very different effects, and some of those effects make them useful for different people. For example, some parts of the HF bands, when the atmospheric conditions are right for it, get reflected off the ionosphere allowing your signal to ‘bounce’ and go much further than line of sight. This is called Skywave transmission.
This leads to amatuer radio operaters being very interested in solar weather, and why we have band conditions as a link on the top of every page on the site.
The next article in our education in this introduction to radio is called ‘Radio All Around Us’ and explores the ways in which radio is the definitive technology of the information age. There is also an article on the discovery and history of radio. We are also working on several articles about what ham radio operators do, from participating in contests, trying to reach far off places (called “DX” in radio jargon), using computing power to process radio signals with Software Defined Radios (SDR), and all of the new weak signal and digital modes.
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