Single-Sideband Modulation

a method of controlling electrical waves by transmitting an information signal on only one sideband of frequencies. This process is used mainly in single-sideband communication, radio-telemetry, radio control, and television.

With amplitude modulation, information is ordinarily contained in each of two sidebands:

ω^c – (Ω_l/Ω_u) and ω_c + (Ω_l/Ω_u)

With single-sideband modulation, however, the carrier frequency (carrier wave) and the frequencies of one sideband are usually suppressed (see Figure 1). As a result, the frequency band filled by the signal is cut to approximately half its original width, and twice the number of communication channels can be allocated to the same frequency range.

Single-sideband modulation can be achieved by suppressing the carrier wave with a balanced modulator and then isolating either the upper or the lower sideband with a band-pass filter. A second method is the phase-compensation method, in which

Figure 1. Spectral composition of electrical waves transmitted by a single-sideband modulation: (U) wave voltage, (Ω_i) lower-sideband frequency, (Ω_u) upper-sideband frequency, (ω_c) carrier frequency. The suppressed waves are indicated by broken lines.

corresponding waves of the modulated (high-frequency) spectrum are balanced out in a nonlinear conversion of the spectrum. The phase-filter method, a combination of these two principles, is also used.