Usage of the 5Ghz Wi-Fi band is increasing. The 5Ghz band was used for 802.11a, introduced in 1999 but 802.11a wasn't widely adopted - later systems such as 802.11b through to 802.11n used the 2.4Ghz band. More recently, the 5Ghz band has been used for 802.11ac and again now for the latest 802.11ax standard. In this article, I'll explain the benefits and downsides of the 5Ghz band compared to the more commonly used 2.4Ghz band.
First, a little basic physics recap. Radio signals exist as waves and can be drawn as a waveform. Wavelength (measured in cm or metres) is the distance from one point on a waveform to its next occurrence - literally the 'length of the wave' for example from one peak to the next.
Frequency (measured in Hertz) is the number of times (or cycles) that a wavelength cycles per second. If you have more waves per second, the distance between each peak is shorter, therefore wavelength and frequency are inversely proportional - increase one and the other reduces, and vice versa.
Waveforms are generally drawn as above - as a graph of amplitude over time but you could also draw it as a circle because a wave (more specifically, a sine wave) rotates from 0 to 360 degrees each cycle. A 1Hz signal would rotate 0-360 ° once a second.
We draw waves as graphs as we can show frequency variations and time but it's still just a stretched out circle. When the waveform crosses the X axis, it's at 0 °, it rises to the peak (90 °), back down to the X axis (now 180 °), down to the bottom of the trough (270 °) and then back to the X-axis (360 or 0 °).
Lower radio frequencies have longer range than higher frequencies. So, a 900Mhz signal would travel further than a 2.4Mhz signal, everything else being equal.
'Short Wave' radio is used by amateur radio (ham) operators, maritime users and long-distance radio stations (world services etc) and international propaganda broadcast. Short wave uses much lower frequencies compared to Wi-Fi, down to around 0.003Ghz (2 MHz) so the longer range is ideal for those applications and can travel thousands of Kilometres. Short wave can increase range further by tropospheric propagation (bouncing the signal off the Earth's troposphere).
Wi-Fi, on the other hand, uses the much higher frequencies, with 5Ghz having lower range than 2.4Ghz, assuming the same power input. There are several reasons why higher frequency has lower range:
This works with sound too. A high-pitched sound will travel less far than a lower pitch sound because higher pitched sounds (a faster oscillation) will excite air molecules more as they travel, losing more energy as heat. So, if you're stuck up a snowy mountain, scream in a low pitch for a better chance of being heard. You won't cause an avalanche (citation).
Those wavelengths (12.5cm, 6cm) are real measurements - that's what you'd measure on a ruler if you could see the microwave signals from your Wi-Fi device. If you want to block radio waves you can build a Faraday Cage (or Faraday shield). A Faraday shield blocks electromagnetic waves. It may be built into the walls and doors of a room and is commonly used for testing wireless equipment, operating MRI scanners or other sensitive measurements where external interference needs to be eliminated.
When you step into a Faraday Cage (room), instantly your mobile phone, your laptop, your pocket radio etc. will lose their wireless signal - dead. This works because as radio or other electromagnetic radiation hits the cage, the charge is distributed around the conductive surface of the shield or cage, but does not penetrate inside; effectively it's a hollow conductor. In the case of a cage, the construction mesh needs to have holes only smaller than the smallest wavelength that you want to keep out. So if you want to block WiFi from your kids bedrooms, you could embed the walls with a metal mesh with holes less than 6cm in size.
You may be familiar with Faraday pouches which are used with keyless card entry fobs. To prevent vehicle theft, the key/fob is placed into a pouch to block its signal from opening the car. Some concert promoters are also insisting that audiences place their phones into faraday pouches, supposedly to engage people more into the moment and prevent recording/photos.
So, given that higher frequencies have lower range, why would we want to use them?
5Ghz still normally has sufficient range for a single office or modest house but if it is insufficient you can mitigate or allow for by having more bases or a mesh system, which can also reduce local congestion.
Higher frequencies have the main advantage of providing higher traffic capacity which in a data environment means higher throughput:
Hopefully you can see that each band offers advantages. If you want the highest speed, the 5Ghz protocols will provide those. If you want the best range or area coverage, 2.4Ghz would be better. You will find that many devices such as home doorbells or security cameras will use 2.4Ghz - in those applications the link speed at 2.4Ghz is sufficient for the application so using 2.4Ghz is going to give the best coverage. Most Wi-Fi routers and access points are now dual-band so if 5Ghz doesn't quite reach the furthest areas, you can switch to 2.4Ghz - which, if the signal is good, is still normally adequate for an HD video streaming service.
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