A doubler is an electronic device that doubles the frequency of an input signal. Doublers are occasionally used in wireless communications to obtain transmission frequencies higher than those normally possible for a given circuit design. A doubler works by introducing nonlinearity into the input signal; that is, the waveform is deliberately distorted. This results in the generation of signals at harmonic frequencies, which are whole-number multiples of the input, or fundamental, frequency. In a doubler, a tuned circuit in the output is adjusted for resonance at the second harmonic of the input frequency (twice the fundamental). The term doubler is occasionally confused with the term splitter. A splitter is a device that allows two signal lines to merge into one line, or one line to be split into two lines, while maintaining a proper impedance match for all the input and output lines. The term doubler is sometimes used in place of the term line doubler, a device that allows TV signals to be displayed on a computer monitor