Joseph Lorenzo Hall, PhD on Nostr: Standard smartphones cannot broadcast a 60 kHz radio wave. But if you play a 20 kHz ...

Standard smartphones cannot broadcast a 60 kHz radio wave. But if you play a 20 kHz square wave at max volume, the physical distortion in the analog amplifier generates a 60 kHz harmonic. The speaker's voice coil acts as a localized magnetic transmitter. 2/4