This system used an entirely different principle-using independently modulated upper and lower sidebands.

Normally the beat frequency is associated with the lower sideband, the difference between the two.

The lower sideband of HD Radio signals on 88.1 also overlap slightly from 87.9 to 88.0.

The signal is amplitude modulated, with the lower sideband suppressed (emission type H3E).

In 1933 Robert Moore, W6DEI, begins single-sideband voice experiments on 75 meter lower sideband.

This can be used to demodulate a type of single sideband signal called lower sideband or inverted sideband.

This can be done by amplitude modulating the speech signal with the carrier, then applying a low-pass filter to select the lower sideband.

Another reason is when the SSB signal is actually a lower sideband, instead of an upper sideband.

The pairing of transmitters offset equally high and low of the isotropic carrier frequency produce the upper and lower sidebands.

Thus the upper and lower sidebands are summed.