Vibration-Induced Phase Noise: It Isn't Just About the Oscillator

Very often, actual, measured levels of vibration-induced phase noise in signal generation equipment are significantly higher than predicted. In many cases, this is because the frequency sensitivity of the oscillator or oscillator resonator to vibration was assumed to be the sole source of the degradation. As improvements in oscillator output signal static phase noise and vibration sensitivity have been realized, the effects of vibration in non-oscillator components and assemblies have become more dominant and cannot be ignored. Primary contributors to vibration-induced signal phase modulation include coaxial cables and cable connectors, narrowband filters, and enclosure mechanical resonances and non-linearities. Accurate measurement of vibration-induced, signal spectral degradation is often difficult due to the influence of both the measurement environment and test apparatus. In addition, isolating and eliminating the cause of out-of-spec hardware performance is time consuming and expensive. This paper will describe potential sources of vibration-induced signal spectral degradation and methods for obtaining and verifying adequately low vibration sensitivity in non-oscillator hardware.