Delayline Oscillator

A Novel Circuit for a 1 to 20-Mc Single-Range Oscillator

A novel use for a variable delay line is illustrated in the schematic diagram of Figure 1. The circuit utilizes the delay line as the feed-back element of a triode oscillator. The delay line may be thought of as a phase-shift network having 180° phase shift at a frequency corresponding to twice the delay time and its odd harmonics.

A simpler physical picture of the circuit operation is obtained from a time-domain description. Let us assume that the triode is suddenly biased to cutoff by a negative voltage step at its grid. A positive voltage step will occur at the plate. This positive step travels down the delay line and is coupled back to the grid by the coupling capacitor, turning the triode on. A negative voltage step then occurs at the plate, which travels down the delay line, cutting the triode off, and the process repeats.

With a large value of coupling capacitor, the grid and plate voltage wave-

Figure 1. Schematic of the delay-line oscillator.



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