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HOW RADIO WORKSRadio wavesRadio transmitters work by supplying a rapidly changing electrical currentto an aerial (antenna), to create a changing electromagnetic field. Thespeed at which these currents change controls the speed at which theelectromagnetic field around the aerial changes. This is measured inhertz (Hz).1Hz 1 hertz 1 cycle per second1kHz 1 kilohertz 1 thousand cycles per second1MHz 1 megahertz 1 million cycles per second1GHz 1 gigahertz 1 billion cycles per secondConsider the image of a pebble dropped into a pond, with the pebblerepresenting the transmitter. The radiating ripples represent thefluctuating electromagnetic fields. These fields are called radio waves,and they radiate out from the aerial at the speed of light.Marine VHF radio operates at a frequency of approximately 156MHz,while MF/HF (single sideband or SSB) radios operate at frequencies fromabout 2MHz to 22MHz.Frequency characteristicsThe different frequencies have different characteristics for specificpurposes, and are subdivided into bands:RADIO HANDBOOK7