All modulators and SSB upconverters require that at least one of the input frequency bands (carrier or modulation) has sufficient power to turn on the semiconductors. All modulators yield a frequency spectrum that utilizes both sidebands on either side of the output suppressed carrier. SSB upconverters, however, employ an internal IF 90° hybrid to yield only one RF sideband output. This is offset above or below the input LO by the IF frequency.
Schottky diode (standard) modulators have the greatest speed and bandwidths, but yield RF output powers of typically less than 0 dBm. Greater output power can be achieved by using higher level diodes with proportional increases in carrier power. Some carrier driven units are used
when the modulation input to RF output must be linear (low harmonics). A typical application is for digital QPSK with cosine shaped pulses (for minimum bandwidth). Many SSB upconverters also require input-to-output signal linearity, thus requiring LO drive. | 
