In this paper, we propose two procedures for accurate amplitude and phase estimation of multifrequency signals in rotating machinery. The first method reduces the amplitude attenuation and phase shift caused by the "nonflat" top of the main lobe of the window. The second procedure is able to reduce not only the leakage effects due to windowing but also the distortion that appears when the rotation frequency changes slowly. This second method uses an additional sensor, giving one pulse per revolution, to transform the input (asynchronous) signal into a synchronous signal having a fixed number of samples per revolution. The performance and effectiveness of both procedures are illustrated by means of simulation examples.

In this paper we apply subsampling techniques to capture the temporal input-output relationship of RF power amplifiers. This approach avoids the distortion introduced by the upconverter and downconverter stages. We develop polynomial models with memory from the available data and evaluate their performance by estimating device parameters like adjacent channel power ratio (ACPR) and AM-AM curves. The estimated parameters show good agreement with the empirical ones.Index Terms-Adjacent channel power ratio (ACPR), AM-AM curve, nonlinear modeling, power amplifier, subsampling.

Phase correction by digital filtering is a common approach to achieve simultaneous sampling with no additional hardware. In this paper we obtain a bound for the interpolation error as a function of the oversampling ratio of the input signal and the interpolation filter order. This bound can be used to analyze and design simultaneous sampling systems by digital phase correction. The obtained theoretical results are validated through simulation. Finally, a vibration analysis system using this technique is described.

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