Probably because while the signal is carried at 19 kHz, its bandwidth is wider. Assuming it's 6 kHz wide would make it 16-22 kHz. You can't send data that is ju

Probably because while the signal is carried at 19 kHz, its bandwidth is wider. Assuming it's 6 kHz wide would make it 16-22 kHz. You can't send data that is just 19 kHz because it's just a static sine wave.