<P> which is the classic model of suppressed - carrier double sideband AM . </P> <P> One method of producing an SSB signal is to remove one of the sidebands via filtering, leaving only either the upper sideband (USB), the sideband with the higher frequency, or less commonly the lower sideband (LSB), the sideband with the lower frequency . Most often, the carrier is reduced or removed entirely (suppressed), being referred to in full as single sideband suppressed carrier (SSBSC). Assuming both sidebands are symmetric, which is the case for a normal AM signal, no information is lost in the process . Since the final RF amplification is now concentrated in a single sideband, the effective power output is greater than in normal AM (the carrier and redundant sideband account for well over half of the power output of an AM transmitter). Though SSB uses substantially less bandwidth and power, it cannot be demodulated by a simple envelope detector like standard AM . </P> <P> An alternate method of generation known as a Hartley modulator, named after R.V.L. Hartley, uses phasing to suppress the unwanted sideband . To generate an SSB signal with this method, two versions of the original signal are generated, mutually 90 ° out of phase for any single frequency within the operating bandwidth . Each one of these signals then modulates carrier waves (of one frequency) that are also 90 ° out of phase with each other . By either adding or subtracting the resulting signals, a lower or upper sideband signal results . A benefit of this approach is to allow an analytical expression for SSB signals, which can be used to understand effects such as synchronous detection of SSB . </P> <P> Shifting the baseband signal 90 ° out of phase cannot be done simply by delaying it, as it contains a large range of frequencies . In analog circuits, a wideband 90 - degree phase - difference network is used . The method was popular in the days of vacuum tube radios, but later gained a bad reputation due to poorly adjusted commercial implementations . Modulation using this method is again gaining popularity in the homebrew and DSP fields . This method, utilizing the Hilbert transform to phase shift the baseband audio, can be done at low cost with digital circuitry . </P>

The typical bandwidth of a dsb am voice signal is