Sailing by

What Radio 4 would look like if you could see it

Most of us can perceive a spectrum of colours ranging from red through to violet, the visible spectrum being just one part of the wider electromagnetic spectrum ranging from radio waves through to gamma rays. As radio waves and light are essentially two different forms of electromagnetic radiation I wanted to consider what it would be like if our eyes were tuned differently to see the waves of Radio 4.

Some insects such as bees see beyond the violet at the end of our visible spectrum to pick up ultraviolet light. Similarly snakes see beyond the red at the other end of our spectrum to pick up infrared. The world is awash with many kinds of electromagnetic radiation sailing by at the speed of light which machines and some creatures can detect but most of which we ignore.

In simplified terms electromagnetic radiation is made up of tiny packets called photons which oscillate in waves to carry energy from one place to another. The difference between each type of radiation is down to the length of the waves and the frequency of the oscillations.

Each colour of the rainbow has a different frequency just as each radio station has a different frequency. In analogue broadcasting each station has a carrier wave which is modified or modulated according to the content being broadcast. The frequency of the carrier wave is the number you use to tune your radio.

With amplitude modulation (AM) the strength of the signal being transmitted is varied by the audio input. When there’s a period of silence the signal stops, and during peaks of speech or music the signal is at its strongest. If you could see the signal from an AM radio mast it would look like a pulsing light, each station’s distinct frequency appearing a different colour.

With frequency modulation (FM) the strength of the signal is constant but the frequency is shifted a tiny amount by the audio input. When there’s a period of silence there’s a fixed signal, and speech or music makes the frequency wobble. If you could see the signal from an FM radio mast it would look like a light with constant brightness with the colour subtly shifting up and down the spectrum.

I sought the help of my brother Richard, an electronics engineer, to demonstrate the changing colours of FM radio in real time. To see FM requires three steps. Firstly the carrier frequency needs to be shifted to one within our visible range; secondly the modulation needs to be increased so the colour changes are clearly perceptible; thirdly the signal needs to be looked at in blocks so it doesn’t appear as a blur.

My brother wrote some software which takes an audio input and modulates a signal in the same way as an FM transmitter although in this case it outputs colour to a screen not a signal to a radio mast. For simplicity we centred the output on green, extended the modulation to include the full colour range of a computer monitor from red to blue, and looked at 0.5 second blocks at a time.

The image for this article shows a fragment of Sailing By which is broadcast every night on Radio 4 at around 0045 UK time immediately before the late shipping forecast. I find it soothing to imagine that while most people are sleeping the UK is being illuminated by the wobbling colours of this classic tune. If only we could see it.

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