must double the audio frequency used

In AM the amplitude of the audio frequency (AF) modifies the amplitude of the radio frequency (RF)

The process of combining a radio frequency with a current at audio frequencies is known as heterodyning. Looking in more detail at the process; the heterodyning process combines the two frequencies, leaving the RF unchanged but producing new frequencies at the sum and difference of the RF and AF.

When using sky wave propagation for communication, the differing refraction occurring at different frequencies leads to an increase in distortion if the bandwidth is too large. The ionosphere comprises electrically charged particles which cause high levels of static interference on radio waves, the use of SSB significantly reduces the effect of this interference. The MF & HF frequencies used for long range communication are in great demand, hence the use of SSB transmissions increases the number of channels available. The use of SSB also reduces the amount of power required. Thus the main advantages of SSB are:

Double the number of channels available with double side band

Better signal/noise ratio (less interference)

Less power required hence lighter equipment

The frequency deviation is primarily dependent on the amplitude of the AF; the greater the amplitude the greater the frequency deviation. The frequency of the AF determines the rate of change of frequency within the modulated RF.