Taking to the airwaves: Amateur radio
Marconi’s trans-Atlantic transmission was a massive hit, and it wasn’t long before a radio was something the soldiers in the trenches of WW1 could make with a pencil and a razor blade. And as the costs came down, a hobbyist scene of skilled people also embraced radio and took to the airwaves, using it to communicate around the world. One of the people who does this is Mike Zero Delta Charlie Victor, aka Peter Howell, Who told Chris Smith the next key part of the story, which is how radio signals are produced in the first place and information like speech is added to them...
Peter - Oh, it goes back about 25 years, when my eldest son came home from school and said he wanted a counterbalance to schoolwork, and I'd always been interested in radio. I had a friend who was in the Cambridgeshire District Amateur Radio Club. So we joined, did the courses, took our exams, got our call signs. And the rest, as they say is history.
Chris - But that club can trace its origins back a very long way, can't it? I mean, I mentioned World War One there, and the Cambridge club is about a hundred years old.
Peter - Yes, indeed. We've got documents taking us back to roundabout 1919, 1920. So we're one of the oldest in the country.
Chris - I bet your gear's a bit better than theirs though?
Peter - Uh, yeah, it's improved a bit since the old spark transmitter days.
Chris - Well, who have you spoken to? And do you literally do this in your back bedroom? Is this the sort of hobby that it is?
Peter - I have a shack in an outbuilding, they're always called shacks, and you speak to people all over the world. And I guess the ones that are most memorable, the first one I ever contacted once I got my license was a guy in Devon, and the other, there's two others that stand out. One was around Christmas time with a guy in Finland who was snowed in for three weeks. He's a farmer in the summer and a forester in the winter. And when he's snowed in, he just goes on the radio and had a very long chat. And the second one I remember was talking to a guy in Florida who had a HF radio in his truck, and he just arrived at work in the morning, had sort of five minutes to spare and had a chat with him while he was sitting in the car park at his place of work in Florida. But that sort of, kind of typical, I guess.
Chris - You mentioned that you had to do various exams and certifications in order to be able to do this. What's involved?
Peter - There's three levels of license, if you like. The first one is the foundation license. And that allows you to transmit with about 10 Watts of RF power. And that's enough to get you all over Europe, into Russia. And when the propagation is good, into North America, and when the propagation is really good, worldwide. The next stage is the intermediate license. And that gives you access to 50 Watts of RF power and a few more frequencies. And with an intermediate license, you can then build your own equipment as well. And then the top level one is the full license and you can transmit with up to 400 Watts, build your own equipment and use all the amateur frequencies.
Chris - Can you talk to the space station? Because I'm sure I've spoken to someone before who said that they had booked a time and they were having a chat with people on the international space station.
Peter - Yes, indeed. Some of the astronauts have a radio license and in the two metre band, you can book a slot and talk to them as they come over and it's a very popular demonstration in schools. I've not done it personally, but I know people who have.
Chris - You mentioned the propagation, you said when the propagation is good, what did you mean by that?
Peter - It's linked to the sunspot cycle, which is the 11 year cycle of activity on the Sun, and we're just going into cycle 26. I think it is. And as the number of solar flares build up, and the amount of ultraviolet light coming off the Sun increases, the ionosphere, which is used to refract radio signals round the curvature of the Earth becomes more active, more refractive, and you can get some amazing distances on very minimum amounts of power.
Chris - So you basically bounce your signal from your antenna on the Earth's surface, up onto that notional layer of charged particles out in space, and then it reflects it, and refracts it more accurately, down to another space on the Earth's surface.
Peter - Absolutely right. So it refracts off the ionosphere, and then 70% of the Earth's surface is covered with water, which is a good reflector, bounces off the ocean back up to the ionosphere, and in three or four hops, that's how you get round to Australia.
Chris - Goodness me. Now let's sort of bite the bullet now then, because you have to answer the crucial question, because so far we've learned about making radio waves. We've learned how they did it back in the early days, and set people's eyes popping out of their heads with those demos, which would have been almost like magic, I would think, to the audiences in those lecture theaters, when Lodge and his colleagues were doing this, but when we want to apply voice to radio, like we're talking now, how is that done? Because how do you take just a signal, an electrical signal, and actually make it so that you can apply information to it that can be received.
Peter - I suppose the easiest way is by CW or carrier wave, where you turn your transmitter on and off to generate the CW characters, just like sending Morse with a lamp, which is what it is. Second way is by means of amplitude modulation, where you blend your voice, or you impose your voice pattern onto the radio frequency carrier wave. And it varies the height, or the amplitude of that wave in sympathy with the audio pattern of your voice. So the envelope, it gives you an analog. The varying envelope gives you an analog of your audio signal, and a third way of doing it is by frequency modulation. And here you keep the amplitude constant, but you vary the frequency as an analog of your voice signal. It's a bit like the bellows on an accordion. As the accordion plays, they stretch and contract. So the frequency increases and decreases in sympathy with your voice. So you sort of wobbled the frequency and then you can demodulate it at the far end in your receiver.