Editing Spark-gap transmitter (section)

====Induction coil====
An [[induction coil]] (Ruhmkorff coil) was used in low-power transmitters, usually less than 500 watts, often battery-powered.  An induction coil is a type of transformer powered by DC, in which a vibrating arm switch contact on the coil called an [[interrupter]] repeatedly breaks the circuit that provides current to the primary winding, causing the coil to generate pulses of high voltage. When the primary current to the coil is turned on, the primary winding creates a magnetic field in the iron core which pulls the springy interrupter arm away from its contact, opening the switch and cutting off the primary current. Then the magnetic field collapses, creating a pulse of high voltage in the secondary winding, and the interrupter arm springs back to close the contact again, and the cycle repeats. Each pulse of high voltage charged up the capacitor until the spark gap fired, resulting in one spark per pulse. Interrupters were limited to low spark rates of 20–100&nbsp;Hz, sounding like a low buzz in the receiver. In powerful induction coil transmitters, instead of a vibrating interrupter, a [[Induction coil#Mercury and electrolytic interrupters|mercury turbine interrupter]] was used. This could break the current at rates up to several thousand hertz, and the rate could be adjusted to produce the best tone.