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The limitations of the usual types of standard-signal generators are discussed and alternative generating schemes applicable to frequency measurements in the microwave region are analyzed. A secondary frequency standard is described which nakes use of a multiplier chain based on a stabilized quartz-crystal oscillator. The voltages at different frequencies are summed and applied to a silicon-crystal harmonic generator. It is pointed out that the silicon crystal is an excellent nonlinear element for the generation of harmonics in the microwave range. The result is an extremely wide output-frequency spectrum. In the particular frequency standard described, frequencies are generated to at least 10,000 megacycles. Identification of the harmonic frequencies is by means of a coaxial-line-type wavemeter, and detection is by means of a super-heterodyne detector. The standard has been successfully employed in the microwave range, being no more difficult to use than the conventional secondary standards used for frequencies below 50 megacycles.