Editing Single-sideband modulation (section)

===Hartley modulator===
An alternate method of generation known as a '''Hartley modulator''', named after [[Ralph Hartley|R. V. L. Hartley]], uses [[phase (waves)|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.

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<ref>[http://home.earthlink.net/~christrask/pshift.html Earthlink.net], listing numerous articles.</ref> 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 [[Amateur radio homebrew|homebrew]] and [[Digital signal processor|DSP]] fields.  This method, utilizing the [[Hilbert transform]] to phase shift the baseband audio, can be done at low cost with digital circuitry.