An experimental investigation was made of Schottky-barrier diodes of two types (based on InP and GaAs), which were used for frequency conversion in the submillimetre, near-IR, and mid-IR ranges. At wavelengths λ=0.8–10 μm the InP diodes proved to be more efficient frequency converters, whereas in the submillimetre range the GaAs diodes were more efficient. Beat signals with the difference frequency up to ~1.7 THz in the region of λ=10 μm were obtained for the first time from the InP diodes. The GaAs diodes were more efficient as video detectors in the submillimetre and IR ranges. The Schottky diodes were used in an optical clock system.