How does Bluetooth work?

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Welcome to Crowd Science from the BBC World Service, the show that answers your science questions. I'm Caroline Steele and I'm standing in a barn in Switzerland, watching two scientists scientists run up a rickety ladder to gather some very precious cargo.

So we have the four juvenile owls now here in our close bags and we will now start to measure them and take them. Oh my gosh, so in that space of time, like a minute, you caught four owls. Baby owls.

And you are carrying three dead rodents? Yeah, exactly. So that's their food reserve. So we will now determine the species, measure them, weight them, so we just have a rough

idea of what they eat. We're here thanks to a question from one of you, which you're probably going to think has nothing to do with owls. But stick with me, all will become clear later in the show.

This week's listener happens to live quite close to home, so we jumped on a train to meet her in person. My name is Rachel, I live in Cambridge in the UK. My question for crowd science is how does Bluetooth work?

Is there any particular moment where you thought of this question? Yeah, so on my commute to work, as I call through the fields in Cambridge, I listen to a podcast or some music along my journey. And I was just wondering how does my phone connect to a device like my headphones and

transmit such a clear signal? We're often in a room with multiple people that they've connected to their headphones, and how do the devices not get their metaphorical wires crossed? Yes, you know that accidentally sort of tune into someone else's music, do you?

Well, I think we need to ask an expert. I agree. Which we conveniently happen to be sat in the living room of an expert because unusually for crowd science, we've managed to get everyone together in one space. So could you introduce

yourself please? I'm William Webb. I'm a telecoms expert and I've been working for 35 years now in the the world of mobile communications. So I've actually lived through the whole process of the invention of Bluetooth. I can certainly remember a time when people thought it was

just a crazy idea and would never catch on and never be used. So it's great to be sat here talking about it now. My first memory of Bluetooth is sending ringtones to my friends at school, which at the time felt incredibly futuristic. Now today ringtones have obviously gone out of fashion, but

Bluetooth certainly hasn't. I use it to send photos, to type on my wireless keyboard and like listener Rachel to listen to podcasts. And all of that without a single wire. So how does Bluetooth actually work? So if we take the example that you mentioned of Bluetooth working with your headset playing some music or a podcast whilst just cycling along. What's actually happening here

is first of all the phone itself is getting that content. It's then transmitting a radio signal from a Bluetooth chip, a special Bluetooth chip on the phone, and that radio signal travels in all directions including towards your headphones. And that radio signal is being what's called modulated, it's being changed by the phone in a way that reflects the music. So the music will be digitally

stored, it will be a sequence of ones and zeros. And what in essence happens is that radio signal will be made slightly louder for a one, slightly weaker for a zero. This signal will travel to your headphones, they have a little antenna, and then they'll be able to notice it getting louder and weaker, and they'll turn that back into ones and

zeros. And then they need to turn that into actual music, and then you hear it in your ears. So that in a nutshell is how it all works, but of course there's a lot more to it than that.

Okay, so let's go through that step by step. So you said that Bluetooth uses radio waves to send information. Can you explain how it does that exactly? Yeah.

So radio waves are actually something that's called electromagnetic waves. And in fact, light is part of the electromagnetic spectrum. So radio waves are in fact just a lower frequency version of light. And frequency, it's how many waves you see in a particular period of time.

So if you imagine waves crashing on a beach, if you had one every 10 seconds, that might be a low frequency of waves. But if you had 10 every second, that would be a much higher frequency of waves. And you get the same thing in radio waves.

There's a wide range of different frequencies. Why, if they're transmitting radio waves, why do you never sort of accidentally pick up some Bluetooth when you're tuning a radio to a certain frequency? So every single use of radio, and there are thousands of them, television and radio

and cellular and so on, is allocated its own little bit of the radio spectrum. And therefore they don't need to fear with each other. If you go back to the old days of tuning a radio with a dial, that tuning range would be well below as it turns out it's a much lower frequency than is used by Bluetooth.

So that radio would never get up to the Bluetooth frequency, which is 2.45 GHz, which is 2.4 billion waveforms per second. So Bluetooth sends information using radio waves of a specific frequency. But why did the engineers behind it choose 2.4 billion waves per second?

There's a lot of history to that, which is actually quite interesting. And in fact, we'll head through to the kitchen where we can pick up on some of that because