The Power Spectrum of a Narrow Band Noise Passed through a Nonlinear Impedance Element

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Abstract
The power spectrum of the current flowing through a nonlinear impedance element excited by a narrow band of noise centered at 1.6 mc has been measured experimentally from the audio range through the sixth harmonic band. A noise having the spectral shape of an error function with a standard deviation of 3.8 kc was generated by passing the current from a photomultiplier tube through several tuned amplifier stages. The noise was applied through an attenuator of 50 ohms characteristic impedance to a type 1N34 crystal diode. The current flowing in the diode passed through attenuators of 50 ohms characteristic impedance to the spectrum analyzer. In the audio range, a conventional wave analyzer was used, and in the remaining ranges, a calibrated radio receiver was used to measure the spectral distribution of output power. The results are in qualitative agreement with the theory of Middleton. A possible reason for the poor agreement is the difficulty of expressing the diode characteristic in a simple form for the computations.

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