An earphone antenna includes an audio signal transmission path formed by
connecting a first shield wire of a coaxial cable to a ground, connecting
a central conductor of the coaxial cable to a pair of first signal lines
of an earphone cable via a capacitor which exhibits high impedance in a
frequency range of audio signals and low impedance in a frequency range
of high frequency signals, and connecting a second signal line and a
grounding wire, respectively, to the pair of first signal lines via a
high frequency choke which exhibits low impedance in the frequency range
of audio signals and high impedance in the frequency range of high
frequency signals. Connecting the second shield wire to the ground causes
formation of a sleeve antenna by the earphone cable and the second shield
wire.
