Frequency Jamming

Suppose one desired a noisy emitter of electromagnetic waves at all frequencies simultaneously. Such a device might be useful to jam undesired cell phone signals, for example. How could you do this simply?

Answer

A spark gap usually is a wonderful noisy source of electromagnetic waves at all frequencies simultaneously. The greater the current across the gap, the more intense will be the total radiation emitted at each frequency. There will be a distribution of intensity versus frequency that can be “tuned” a little by adjusting the gap spacing.

A simple spark gap would be a small battery, such as a D cell, and two wires in the process of making contact. Held near a radio, the small spark across the gap can be heard through the radio, indicating that many frequencies are being emitted. As an additional demonstration, one can even move a radio near a small electric motor of the kind that has brushes to hear its rotation frequency because the brushes make and break contact each revolution.

Of course, if one desires to have a higher-current spark gap, a car battery or a transformer can be used with proper safety precautions to provide a healthy current that can be operated in an intermittent mode or in a continuous mode. Nearby radios, televisions, and so on will be affected by this larger-current spark gap device. Even GPS transmissions between 1,000 MHz and 2,000 MHz may be affected, so some care must be taken not to violate federal transmission limitations.