Showing posts from May 2018
Radio waves form part of the electromagnetic spectrum, just like microwaves, infra red and light.They all travel at the same speed, but their frequency, and therefore wavelength, vary.
Radio waves have the lowest frequency and the longest wavelength of the different parts that form the electromagnetic spectrum. We are talking in the order of kilo hertz (like the long wave radio) up to Giga hertz (like parts of the mobile networks or satellite communications).
Radio waves towards the very bottom end of the spectrum tend to have a longer range, but because of that they there’s normally more interference, and you need a bigger antenna. Remember the big aerials we used to have on our cars, or perhaps the even bigger ones truckers had for CB..?
If, like me, you like to listen to the cricket on the radio then the only option used to be radio 4 on long wave – a very low frequency at just 198 kilo Hertz. The coverage was amazing, with holiday makers in France being able to tune in, though the sound quality not always great.
If you wanted to listen to radio 1 or 2 or whatever, then you need FM, so around 100 MHz….The downside of lower frequencies is that you can’t send as much data. The sound quality on Long wave is nowhere near as good as FM.The faster the frequency the more waves there are every second, so you can fit more information in…. So you have more bandwidth.
Most people associate broadband with home internet so high speed data, but normally arriving at your doorstep via cable or fibre. Narrow band radio waves have a longer range, but lower data rates, and achieve that using less power. Broadband is the opposite, but why? With narrow band we are taking all the energy and squeezing it into a narrow band of frequencies, but because there’s only a narrow band then we can only squeeze so much data through it. To get more data throughput we need to increase the bandwidth -> broadband but this means the energy is spread out.
We want lower power firstly because it’s great when you can run from a battery and not have to connect to the mains, but also so we can comply with the regulations as each frequency band has a maximum power output. Sigfox and LoRA are both narrow band technologies – so we see excellent range but pretty slow data rates. For sensor readings we rarely need fast data rates.These technologies compliment other wireless sensor communication options. The following table gives a quick summary of the main differences.