The speaker coil in a dynamic speaker in a mobile computing device can be used to generate radio frequency (RF) signals having a frequency of about 100 kHz or greater. A speaker amplifier drives the dynamic speaker to produce sound and RF circuitry drives the speaker amplifier to generate the RF signals having a frequency of about 100 kHz or greater. The speaker coil can comprise a tap at an appropriate point between the ends of the coil to cause the coil to operate at resonance over a desired RF frequency band. A low-pass filter can be positioned at the speaker amplifier output to protect the speaker amplifier from RF energy generated by the RF circuitry and a high-pass filter can be positioned at the output of the RF circuitry to protect the RF circuitry from audio energy generated by the speaker amplifier.