Smith, D.C. 1993. High Frequency Measurement and Noise in Electronic Circuits. Van Nostrand Reinhold, New York. [Pg.40]

About measurements in the presence of a high-frequency noise [Pg.208]

Figure 10.16 Ideal noise spectral density versus frequency. Note the increase at low frequencies, the flat region ( white noise ), and the eventual falloff at very high frequencies. Measured data will not be as smooth, and will have spikes at some frequencies due to external source (60 Hz power, fluorescent lights, etc.). |

The main error sources are noise in the wavefront sensor measurement, imperfect wavefront correction due to the finite number of actuators and bandwidth error due to the finite time required to measure and correct the wavefront error. Other errors include errors in the telescope optics which are not corrected by the AO system (e.g. high frequency vibrations, high spatial frequency errors), scintillation and non-common path errors. The latter are wavefront errors introduced in the corrected beam after light has been extracted to the wavefront sensor. Since the wavefront sensor does not sense these errors they will not be corrected. Since the non-common path errors are usually static, they can be measured off-line and taken into account in the wavefront correction. [Pg.195]

The presentation of the result in the frequency domain offers an additional advantage. The reactor behaviour modelled (Comb. Chamber (,i) can be directly compared with the behaviour calculated (Comb. Chamberc t,). The calculated frequency response of the reactor is the ratio of Che measured output and input spectra. This comparison is not possible in the time domain due to the measurement noise at high frequencies. This noise is amplified by the compensation of the measurement dynamics and thus no useful presentation of data is possible in the time domain. [Pg.580]

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