I started writing a quick primer on radio waves within an article on how to get into Amateur Radio (upcoming), but it quickly expanded to the point where I decided it deserved its own article. So, want a little refresher on the basics of radio waves? Read on!
The Electromagnetic Spectrum
Electromagnetic (EM) radiation is all around us. Radio waves, microwaves, visible light, x-rays, gamma rays and more are all examples of EM radiation, they all have their place in the EM Spectrum (shown below), and they are all waves. The only difference between them is their frequency and wavelength.
The frequency of a wave is the rate at which the wave repeats itself (or cycles). One wave cycle per second is one Hertz.
We’ve developed technology that allows us to convert radio waves of a specific frequency to sound that we can hear. These are the radios we have in our homes and our cars!
When we set our dial to 98.8 Mhz FM to listen to BBC Radio 1, we’re telling our radios to focus on the FM radio waves that are cycling at 98,800,000 Hertz! (1 Mhz or Megahertz = 1,000,000 Hertz). Okay, FM it’s a bit more complex than that, but that’s all we need to know!
Amplitude the measurement of the strength of the wave.
- If the wave were a sound wave, a higher amplitude would give us a louder noise
- If the wave were a radio wave, a higher amplitude puts more power behind the wave, allowing it to travel further, and be received better over background noise or other transmissions
- Your electrical appliances are also rated in amps (short for amplitude). Some of them use more power than others, and thus have a higher amp rating!
The higher the amplitude, the more energy the wave has.
Amplitude is measured as half the height of the wave. Look at the below diagram. Both waves have the same frequency, but different amplitudes. The wave at the top of the diagram has a higher amplitude, and so it is “taller”. If you’d like a more dictionary-like definition of amplitude, look no further than….right here!
“Amplitude is the objective measurement of the degree of change in the power output of a wave”
Wavelength! The length of a wave
The physical length of a wave (quite handily called the wavelength) is the distance between the start and end of one cycle of the wave (see below diagram). Some low frequency waves are more than 100 miles long, some higher frequency waves are less than 1 millimeter long!
Bands and Channels
(Not actually to do with the basics of radio waves, but Band and Channel are terms used often in the world of radio transmission and reception.)
A band is a specific slice of the EM Spectrum. For example, CB Radio users transmit at around 27 Mhz. This is part of the 11 Meter Band of frequencies, because a 27 Mhz wave is about 11 meters long (it’s actually about 11.11111…. meters long).
Channels (E.g TV channels) are specifically designated frequencies within a band that people can tune their sets to. There’s usually a gap between channels to avoid accidental cross over.
Modulation. It’s not as difficult to wrap your head around as it first sounds! Let’s look at two very well known methods of radio modulation. Frequency Modulation (FM) and Amplitude Modulation (AM). Put simply, these are two different methods of formatting a piece of information in order to transmit it. The piece of information we want to send is represented in the below diagram as the “Signal”. Let’s say that signal is somebody’s voice speaking into a microphone.
In Amplitude Modulation (AM), the transmitted wave’s frequency does not change relative to the source “Signal”, but the amplitude does.
In Frequency Modulation (FM), the transmitted wave’s amplitude does not change relative to the source “Signal”, but the frequency does.
A radio set that can only demodulate (restore the original “Signal” so it can be played out of the speakers) AM transmissions would be unable to retrieve the information from an FM transmission, and vice versa. For example, in the UK, CB Radio uses FM. In America, CB Radio uses AM. Even if you had favourable weather conditions and an excellent antenna, you would never hear a normal American CB user on the same frequency using a UK FM set.
Interested in where Amateur (HAM) Radio & CB Radio sit in the EM Spectrum? Take a closer look at that diagram!
Now you know the basics of radio waves you guys! Don’t forget to check out my upcoming article on How to get into Amateur Radio, because you know, it could be pretty rad.