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Rough Science 4 Death Valley: Jonathan Hare's diary: Communication

Updated Tuesday 29th August 2006

Jonathan Hare's diary about the challenge for the Communication programme, from the BBC/OU series Rough Science 4

Jonathan and Kathy make some light convarsation Copyrighted image Icon Copyright: Production team

Day One

Kathy and I are set a particularly tricky challenge today: to find a way of transmitting a voice without using sound waves. We decide to use light instead, by making a light beam transmitter! The idea being that using some basic equipment you can encode (modulate) your voice onto a light beam, send it over a distance and pick up the beam and its voice message using some other equipment and turn it back into sound. And there you have a light beam communicator (very handy in space where there is plenty of light but no air for sound to travel through).

Kathy makes up a few transmitters – a tube with one end covered in aluminium foil. When you speak into the other end it vibrates the foil and modulates the light that happens to bounce of it. So if you reflect sunlight from the foil and talk into the tube you encode the sound of your voice onto the Sun light.

She makes up a batch of beautiful tubes and has a go at polishing the foil to get a better reflectance and therefore greater efficiency. We need to try a few different designs (tube dimensions, foil area size etc) to see which will work best.

I play around with making the detector – the light beam receiver. This uses the radios that we have been given as an amplifier but crucially we need a modified transistor to pick up the light in the first place. All transistor technology is sensitive to light which (apart from the mechanical advantage) is why the devices are encapsulated in plastic or contained in a tiny metal can. If we cut off the top of the can and use the transistor in a standard amplifier circuit, the small variations in the transistor's behaviour as the light shines on it will cause tiny additional currents to flow in the circuit. With amplification these currents are exact electrical copies of the sound. When these are fed to a loudspeaker it converts the electricity into the sound which you can hear!

I played around getting the transistors out of the radios and, in particular, looking for metal canned, instead of plastic, versions. Then the tops of the transistors were carefully filed off and wired up to a meter. By taking them outside into the bright desert sunshine you could easily see the change in conductivity across the transistor wires between when the device was shaded and then put into the sunshine. This was a very exciting and rewarding moment. Its this sort of moment where I can relax a bit because I know that the fundamentals are all okay. Even though we may have to work really hard to get it to work well, I now know at this point that it is possible and that’s a massive Rough Science moment !

I am often asked if I enjoy working on my own or in a group best. The answer is - both. When I am working in my workshop at home I am very happy to be on my own and work at my own pace, following up whatever idea comes along – I am completely happy. However I have worked in some very successful groups and have also enjoyed that enormously. The thing is, when you work on your own you have the enjoyment of the single-minded focus and absorption. When you work in a group you have the added dimension of other people’s energy and creativity. In all honesty much greater things are possible in a group than are possible while working on your own – the old saying ‘two heads are definitely better than one’ is true - but it is a different experience.

Working with Kathy is often a mixture of feelings. On the one hand she is a very fast thinker and sometimes this makes me feel a little stressed as I am not sure if I ‘feel’ I can keep up. I sometimes want to think really slowly, and it’s almost like I want to savour the ideas and that’s hard to do in a group. On the other hand its always fun to have her high energy and enthusiasm around and, of course, that other viewpoint that a good scientist might have.

Jonathan and Kathy make some light convarsation Copyrighted image Icon Copyright: Production team

Day Two

‘What is the recipe for gypsum?’

Kathy and I go into the mine to test out the mirrors and the receiver. We were told that there are more than 40 miles of mine tunnels in this area! As the door is opened to the shaft a very cool breeze blows out from the mountain side – it’s almost cold in there!

We play around with a small laser pointer and Kathy discovers that the fine spot of the beam is very good at showing which transmitters (tubes) produces the greatest deviation in the beam when you speak into it – i.e. which tube should be the best transmitter. The small diameter tubes produce the best modulation; but they have the least reflective surface to send back the modulated light!

I play around with trying out a better pre-amplifier to boost the signals and also trying to use more than one detector (transistor with the top removed). The tests in the mine shaft showed the principle but the quality of the transmission was poor. Kathy and I go outside to use the bright sunlight and find that not only does it work but the quality is great. I guess we need light coming from all the surface of the foil rather than one spot of it. So we have a working system but in true RS fashion the range is very limited and the clouds are building up – just what we need!

On the way back from the mine shaft we see the most spectacular rain storm over the valley – at times almost blocking out the view of the mountains in the distance. Swirls of misty clouds with sunbeams coming through like the spokes from the glorious wheel of the desert Sun.

On the way back tonight Mike B, Iain and I discuss what should be on the plaque. There's all sorts of good ideas and I suggest that it should contain the letters H, E , L and P running down the middle but Mike B's suggestion was funny - he said the message to the alien life should read "What is the recipe for gypsum?" (because Iain had problems making gypsum.)

Jonathan and Kathy make some light convarsation Copyrighted image Icon Copyright: Production team

Day Three

Kathy and I make up a couple of tripods for the equipment, she also makes up a corner reflector out of three bits of mirrors she cut as well as a rubber covered tube with a piece of glass mirror attached. This might prove to be the best transmitter yet as the mirror works really well.

I set up the receiver on the tripod and also arrange for a magnifying glass to be supported in front of the detectors (transistor) to help collect and focus the precious modulated sun light. This worked really well and a weak signal could be pulled out of the noise using the magnifying glass – it was really spectacular to hear.

We sit out in the blazing heat testing out the range of the equipment. Little by little Kathy and I managed to tweak the system so that we got further and further distances with our light beam communicator. We were still having problems with the weather and clouds blocked the direct sunlight some of the time - light we desperately needed to get the experiment to work.

Then it’s time for the big test: We set everything up and all the crew and Roughies are geared up for the ending of the show. Iain shows us his plaque of Kate’s face. Kathy reads out her secret message talking into the tube and bright sunlight bounces off the mirror that vibrates with her voice. The beam passes the 50 metres to the receiver faster than can be imagined; the magnifying glass collects some of this light and concentrates it on to the transistor. A small changing current is set up amplified by the radio parts and fed to the loudspeaker – we hear, a little noisy but distinctly,

‘Rough Science mission accomplished’!

Mike B accurately transcribes the message onto the paper, upside down using his zero gravity pen using ink Ellen made. A great ending to the Second Challenge.



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