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This paper describes the phase-noise characteristics and the analysis model of an SC-cut dual-mode oscillator. The C mode phase-noise sideband levels of -124 dBc at 10 Hz and -154 dBc at 10 kHz have been demonstrated using a dual-mode oscillator that simultaneously excited the C and B mode of a 10-MHz, third overtone, SC-cut crystal resonator. Based on Leeson's model, a phase-noise analysis model for dual-mode oscillators has been proposed also. Actual phase-noise levels of the C mode in dual-mode oscillation corresponded well to results calculated from the proposed model.

In this study, the subspace stochastic realization theories (SSR model I and SSR model II) have been applied to a real bridge for estimating its dynamic characteristics (natural frequencies, damping constants, and vibration modes) under ambient vibration. A numerical simulation is carried out for an arch-type steel truss bridge using a white noise excitation. The estimates obtained from this simulation are compared with those obtained from the Finite Element (FE) analysis, demonstrating good agreement and clarifying the excellent performance of this method in estimating the structural dynamic characteristics. Subsequently, these methods are applied to the vibration induced by both strong and weak winds as obtained by remote monitoring of the Kabashima bridge (an arch-type steel truss bridge of length 136 m, and situated in Nagasaki city). The results obtained with this experimental data reveal that more accurate estimates are obtained when strong wind vibration data is used. In contrast, the vibration data obtained from weak wind provides accurate estimates at lower frequencies, and inaccurate accuracy for higher modes of vibration that do not get excited by the wind of lower intensity. On the basis of the identified results obtained using both simulated data and monitored data from a real bridge, it is determined that the SSR model II realizes more accurate results than the SSR model I. In general, the approach investigated in this study is found to provide acceptable estimates of the dynamic characteristics of highway bridges as well as for the vibration monitoring of bridges.

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