In radio communications, a side-band is a band of frequencies higher than or lower than the carrier frequency, that are the result of the modulation process. The side-bands carry the information transmitted by the radio signal. The message signal is super-positioned on the carrier wave. Thus, side-bands produced have frequencies,$=$carrier frequency$\pm$message frequency $=3 \mathrm{MHz}\pm 20 \mathrm{kHz} =3020 \mathrm{kHz} \& 2980 \mathrm{kHz}$