RF Wavelength (Guest Blog)

RF Wavelength (Guest Blog)

By Michael Miller On 01/18/2022

My name is Michael Miller and while studying for the CWNA exam I came across some difficulties trying to understand RF wavelengths. The reason for writing this post is to share some of the things I found that helped me understand. Hopefully, this information will reach those who need it and can help them the same way it did for me.

What Is Radio Frequency
Radio Frequency is a range of frequencies in the electromagnetic spectrum. According to WatElectronics "Wireless Radio frequency is any of the electromagnetic wave frequencies around 3 kHz-300 GHz". Radio waves are just a small part of the electromagnetic spectrum. Microwaves are part of the electromagnetic spectrum and part of the RF range, and they also interfere with wireless devices and signals. Microwave ovens are just one example of an appliance interfering with wireless transmissions. It is important to take these appliances into consideration when implementing a WLAN.

Calculating RF Wavelengths

Figure 2 wavelength formula triangle

When calculating the wavelength, you will always have the speed of light (3.0x10^8ms^-1) to put into the formula. The next thing you will need is the frequency of the wave in kilohertz (kHz) or gigahertz (GHz) you may have to convert one to the other in order to cancel them out when dividing. Now that you have two of the numbers you can find the third one (the wavelength) by dividing the speed of light by the frequency to find the wavelength. Looking at the formula triangle makes it easy to remember where to put the numbers and what to do with them. If you were looking for the speed of light you would multiply frequency and wavelength to get it. If you are in a situation where you need answers fast and don't have time to waste doing pen and paper calculations, I would recommend using an online calculator.

Frequency vs Wavelength

Figure 3 Radio waves, television waves and microwaves have different wavelengths.

As the frequency of a wave increases the wavelength decreases. NASA defines a wavelength as "The distance between one peak or crest of a wave of light, heat, or other energy and the next peak or crest". It is important to know that a full wavelength is measured from crest to crest or two identical points on the wave. This means that a 360° rotation is a full wavelength from crest to crest and a half wavelength would be a 180° rotation measured from crest to trough.

The Relationship Between Frequency and Amplitude

It is important to know the difference between amplitude and frequency of a wave when talking about wireless communications. Amplitude is the energy or intensity of a single wave and frequency is the regularity of the wave repetition. If we have two waves with the same amplitude but one has a lower frequency than the other the lower frequency wave can be received farther than the higher frequency wave because antenna design for higher frequencies is more challenging the higher the frequency. Additionally, the higher frequency wave will attenuate faster because it is typically absorbed more easily by elements in the atmosphere and physical objects through which it must pass. A rough analogy is bouncing a basketball. If you let the ball bounce freely it will bounce for longer than if you put your hand over it making it bounce faster. The ball bouncing with a higher frequency loses energy every time it hits the ground and your hand. This is the same with radio waves the higher frequency will lose energy faster when interacting with the environment. While low frequencies can travel longer distances the downside is that they can't carry as much data as the higher frequencies. It is finding the sweet spot between power and frequency that makes the most efficient wireless networks possible.

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Tagged with: rf, wavelength, radio frequency, formula
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