# Fermilab

## Inquiring Minds

Can an audio wave be combined with a radio wave?

You Wrote:
What is the wave called when you combine an audio wave with a radio wave?

Bruce

Dear Bruce,

It is not quite clear to me what definitions you may use for your "audio wave" and "radio wave." So let me state how I interpret your question.

Audio wave: I assume you refer to a sound wave, a wave that is being transmitted through the air at the speed of sound. This wave is being transmitted through gas/liquid/matter by the oscillation of molecules. The sound creates differences in pressure, which triggers the oscillation of the molecules, and one molecule passes the wave onto its neighboring molecules. If there are no molecules (vacuum), there is no wave. Sound cannot be transmitted through a vacuum.

Radio wave: I assume you refer to an electromagnetic wave, which is traveling at the speed of light. The waves transmitted by radio stations are exactly this, and depending on the band (short,long,etc) the waves have different frequencies (radio frequency refers to the range from 10 kilohertz (kHz) to 300,000 megahertz (MHz)) and "encoding methods" (AM vs. FM) to transport the signal. These electromagnetic waves can travel even through a vacuum. They don't need a medium - in contrast to the sound waves. Light is also an electromagnetic wave. It just has a different frequency than the radio waves.

Now to your question: I am not aware that there is a special name for mixing these two different types of waves. As a matter of fact, these two types of waves don't mix. To a very good first approximation, they don't influence each other at all. They pass through each other without disturbing each other. Otherwise every time you speak (sound wave), the reception of your radio (electromagnetic wave) would be affected.

If you mix waves of the same type (sound with sound, electromagnetic with electromagnetic), then you will observe a mixing pattern called an interference pattern. If the frequencies of the two mixed waves are very similar but not identical, you can create something called a beat: the volume (amplitude) of the resulting wave goes up and down and up and down... And if you overlap simple oscillating electromagnetic waves in two dimensions, you can get Lissajou figures.

I hope this helps.

Best wishes,

Kurt Riesselmann
Fermilab

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