The Serrodyne Frequency Translator

A serrodyne frequency translator will translate, or shift, the frequency of a signal in a nearly ideal manner. Linear sawtooth modulation of a transit-time device, such as a traveling-wave tube or klystron, is employed to effect the translation. The power output at the translated frequency is practically equal to the capability of the same device operating as an ordinary amplifier. Furthermore, very little power is produced in undesired intermodulation frequency components. Frequency translations of a microwave signal ranging from subaudio frequencies to 57 megacycles have been accomplished. The translation loss for a translation of about 30 megacycles was less than 1 decibel; moreover, each undesired frequency component was suppressed at least 20 decibels. The serrodyne method can be used at nonmicrowave frequencies and with larger fractional frequency shifts, provided modulable transit-time devices having certain properties can be devised. An analysis is given of serrodyne performance as limited by a number of important practical factors. A general spectrum analysis is included which is in a convenient form for a variety of problems in combined AM and PPM (or combined AM and PM) when arbitrary modulating waveforms are used.