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Some spectrum analyzers (such as "real-time spectrum analyzers") use a hybrid technique where the incoming signal is first down-converted to a lower frequency using superheterodyne techniques and then analyzed using fast fourier transformation (FFT) techniques. Spectrum Analyzer http://en.wikipedia.org/wiki/Spectrum_analyzer
The Ando AQ6317 is an advanced optical spectrum analyzer for a wide range of applications, including light source evaluation, measurement of loss wavelength characteristics in optical devices, and waveform analysis of WDM (Wavelength Division Multiplexing) systems. Especially at 1550 nm band, the unit achieves high wavelength accuracy and wavelength linearity, and can evaluate optical devices for WDM. Teknet Electronics Test Equipment Connection
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