Turn on, tune in
Ask any GCSE student of science what the effect is of cutting an electric circuit with a pair of scissors if it is carrying a current. Stock answer: the current stops. True, with direct and low frequency alternating currents. But at radio frequencies the current doesn't stop: it oscillates backwards and forwards between the broken ends radiating energy that we can use to carry our voice vast distances across the ocean.
In spite of its ubiquity, the huge majority of people have no understanding of what radio is, how it works, or what it can do. The educational charity STELAR (Science and Technology Through Educational Links with Amateur Radio) has been working steadily for 10 years to educate teachers, and through them their pupils, to enjoy radio as an activity in school. While the science of radio is for GCSE and above (with a unit in communications in the piloting science for the 21st century GCSE), all secondary pupils can thrill to radio communication.
People wrongly think that the aim of amateur radio is to speak to people.
What really gives the buzz is taking charge of the science and technology allowing communication with others at the furthest reaches of the planet (and space). Like astronomy, radio science is one of those rare areas in science where the interested amateur can make a real contribution. It is not by chance that about 80 per cent of Nokia's development staff are radio amateurs. Globally, communications are worth somewhere in the region of $200 billion (pound;103 billion) and growing daily.
But what is the science involved in radio? Briefly, one has to generate a high frequency electric current, process it to make it carry an intelligent signal, launch it into the air and capture it at the far end, recovering the intelligence.
Generating such a high frequency current is a technical challenge as it has to be absolutely stable in terms of its frequency. The physics of this involves feedback and the use of a crystal to make a highly stable "clock" that can produce millions of changes in a small electric current each second. The action of the crystal is similar to that of the pendulum in a grandfather clock; it acts as a stable reference for the master oscillator of the radio.
Impressing the intelligence onto this rapidly changing current is called modulation. Students of A-level mathematics and physics may be familiar with the process of adding sine waves together and the products generated as a result. Radio modulation is an excellent practical example. This is one way in which speech can be placed onto a radio wave.
The speech waveform is added to that of high frequency current in a modulator circuit and it "changes its shape". It is these subtle changes in shape of the waveform that can be recovered and turned back into sound.
Coils, resistors, and capacitors are all bread-and-butter devices studied in A-level physics, yet unfortunately dealt with in such a way that pupils think they have little to do with the "real world". They seem simply the plaything of the examiner. Put these components into a communications circuit, though, and they become something capable of sending our thoughts and words across the world. It seems such a pity that most A-level students have little chance to experience the sheer wonder of it. Here is where your radio club can literally turn people on. For primary pupils, the thrill of contacting far-off places has many cross-curricular benefits, from enhancing history and geography to building self-confidence. And it shows them science in action.
Standing waves are studied in most A-level courses. Reflecting a wave back onto itself can make it radiate energy as sound, as in a brass instrument, or a radio wave will radiate electromagnetic energy. This is how many types of radio antennas work.
To illustrate the practical application of standing radio waves, I show the class a dipole antenna which I use as a portable antenna when working away from home. I get up at 4am to catch the sunrise. At that hour I can hook on to some distant radio station using a maximum of five watts of power since as the sun comes over the horizon, the ionosphere above the surface of the Earth behaves as an occasionally perfect mirror for radio waves, reflecting them to distant lands.
The radio antenna used to launch tiny amounts of energy into a maelstrom of energetic particles 150km above my head has to support a standing radio wave along its length. It isn't merely a piece of wire, it is an energy-transferring device that has taken hours to make and hone to perfection. I cut tiny pieces from each end to secure perfect symmetry, the exact length depending on the frequency I decide to operate on. A particular favourite is the 20-metre band, so the antenna is 10 metres long.
I spent time on the internet looking up the velocity factor of this particular type of cable, making a near perfect match with my radio to hurl my signal at the speed of light into space. I start the potential contact:
"CQ CQ CQ CQ. This is golf zero whisky foxtrot golf portable standing by."
"Yes." It's Australian voices, two of them! After hiss and more hiss: "Did you hear something? It's very weak but it sounded like a G station. Hang on, I'll turn the beam antenna towards the UK." I try again, putting the suffix QRP station to my call sign. Immediately comes the reply. "QRP station golf zero whisky foxtrot golf this is victor kilo... " Communication has been established over a link thousands of miles long using less power than that from a torch bulb. Physics, coils, capacitors, resistors, standing waves, modulation, resonance, sinusoidal oscillations, Ohm's law, Maxwell's equations, current, potential difference, resistance, inductance, capacitance, phasors, vectors, standing wave ratios, SinA + SinB, have done their bit to allow two people to interact for 10 minutes.
One stood on a lonely sandhill in Northumberland. The other from his room in Melbourne.
As the sun rises, the ionospheric mirror cracks. The sun's ultraviolet radiation penetrates more deeply into the ionosphere disturbing the delicate balance of electric charges that reflect the signal. The friendly voice in Melbourne fades to nothing. My lonely sandhill seems very distant from the physics lab at school, but just think what physics has made possible.
Further information:STELAR funding includes Ofcom, the Office of Communications, and the Radio Society of Great Britain. The next STELAR course, sponsored by Ofcom, The Radio Society of Great Britain, will be held at Rishworth school, West Yorkshire, on March 29 at 2pm until April 2 at noon. To book, tel: 01422 822636 (evenings); email tony@ gowfg.demon.co.uk; or attend the ASE Annual Meeting. The course is residential and free to teachers, including meals, tuition and accommodation. A pound;30 deposit is returned on arrival and registration.
To learn morse, email firstname.lastname@example.org.
Anthony Vinters (call sign gowfg) teaches science at Rishworth school in West Yorkshire
* Buy the cheapest headset and microphone to plug into your school PC soundcard. Cost, less than a tenner. A radio transmitting licence. Cost, zero. All you need is a training course for the Foundation Radio Licence Exam. Cost, zero.
* Come to Rishworth school in West Yorkshire for the next course.
* Download the program called Echolink, free. Fill in your call sign when requested; the United States server activates any one of about 2,000 radio transmitters dotted across the world. Use these to talk to local radio amateurs. You may be radio-linked to a device called a repeater, a small radio transmitter and receiver located in some prominent location such as a mountain top. The repeater broadcasts your voice so that it can be picked up by a local radio amateur who in turn communicates with you through the repeater linked to the internet. This process allows effective communication over thousands of miles irrespective of radio conditions.
Some argue it is not "real radio" but voice quality is excellent as is reception: in our school we talk to enthusiasts around the globe.
MAKE YOUR OWN RADIO
For all abilities, key stage 4
In the new 21st century GCSE science syllabus, a teacher pack includes a couple of simple crystal radios to be built in school. The basic materials are a piece of wood and drawing pins. The electronic gizmos that make it all work cost about pound;4 and can be put together in a practical session of about 90 minutes. The kits work very well and illustrate important radio principles. The kits can be used with pupils with special needs or key stage 2 as well as GCSE students.
You need a cheap transistor radio with a short wave band. Carefully tune it between 7.0MegaHertz and 7.1MegaHertz. You will hear lots of Morse code at one end and as you go further up the band towards 7.1MHz you will hear voices, sounding a bit like Donald Duck. The reason for the funny voice is that they are using Single Side Band (SSB) which allows many people to talk simultaneously. With a special SSB receiver you can hear each one very clearly. Make a simple buzzer and get pupils to send messages to their friends.