A High-Level Single-Sideband Transmitter

Double-sideband suppressed-carrier signals can be generated with relatively high efficiency at high power levels in grid-modulated balanced modulators so biased that very little plate current flows in the absence of audio input. When tubes having a constant-current characteristic are used, and the necessary quadrature phase shift between pairs of audio- and radio-frequency excitation voltages exists, two high-power balanced modulators of this type may be connected to a common output circuit to produce suppressed-carrier single-sideband signals. The peak efficiency of the combination for sinusoidal modulation is π/4 times or 78 per cent that obtainable when the same tubes are used as linear amplifiers. Operating adjustments are shown to be straightforward. The simplicity and power economy of this circuit make it attractive for those applications where moderately low distortion and reasonably good rejection of the undesired sideband are satisfactory.