Bluetooth 1.x uses a variation of frequency shift keying (FSK)
This variation is called two-level Gaussian frequency shift keying (2-GFSK)
Uses two different frequencies
To indicate whether a 1 or a 0 is being transmitted
The modulated signal is filtered using a filter with a Gaussian response curve
To ensure the sidebands do not extend too far either side of the main carrier
Modulation index
Amount that the frequency varies between high and low
Between 280 KHz and 350 KHz