Amplitude-modulated mechanism

To reduce spurious signals due to drifts of the EPR line setting arising from mechanical and thermal instabilities, double coding of the ENDOR information is often employed23). Normally a low-frequency Zeeman modulation (30-300 Hz) is applied while the rf field is frequency or amplitude modulated at frequencies of about 1-30 kHz. This modulation scheme, however, has two major disadvantages ... 

A widely used practice is to apply a sinusoidal frequency modulation (FM) to the MMW source. This too produces an amplitude modulation of the transmitted signal. Any fi equency dependent component in the MMW transmission line, whether it be a sample, a cavity or a reflecting component, will show similar behaviour. It is important to minimise those spurii by careful construction and attention to mechanical matching of components such as coaxial connectors and waveguide flanges. 

Modulators are needed to convert electrical signals into optical amplitudes or phase modulations. Polymeric waveguides may be more compatible with integrated optics owing to processing considerations, and will be much cheaper to manufacture. Routing switches, electrooptic shutters, and amplitude modulators are imponant components for optical communications networks. Directional couplers, mode sorters, and Mach-Zender interferometers (Figure 2) are representative of the specific device mechanisms. These devices can op-... 

The LOAS instrument consists of the following main units A tunable laser, a sample cell with an acoustic transducer (sometimes called a spec-trophone or SP), an amplifier, and a recording system. The acoustic response of the medium can be stimulated by amplitude or frequency modulation of the laser light or by Stark or Zeeman modulation of the absoiption line of the analyte. Both pulsed and cw lasers with mechanical or electro-optical amplitude modulation are often employed in LOAS analytical applications. 

The generator works by producing a sequence of dampened sinewave bursts. A single note contains a number of these bursts. Each burst has its own local envelope with either a steep or a smooth attack, and an exponential decay curve. The formant is the result of this local envelope. As the duration of each FOF burst lasts for only a few milliseconds, the envelope produces sidebands around the sinewave, as in amplitude modulation. Note that this mechanism resembles the granular synthesis technique, with the difference that the envelope of the FOF grain was especially designed to facilitate the production of formants. 

The significance of instrument band width and modulation transfer function was discussed in connection with Equation (3) to characterize the roughness of nominally smooth surfaces. The mechanical (stylus) profilometer has a nonlinear response, and, strictly speaking, has no modulation transfer function because of this. The smallest spatial wavelength which the instrument can resolve, 4nin> given in terms of the stylus radius rand the amplitude aoi the structure as... 

The audio signal resulting from rf amplification and detection is amplified and detected in a phase sensitive manner by using the original modulation phase as a reference. Both mixer vacuum tubes 6S) and mechanical choppers are used. The resulting DC voltage is fed into a recorder. For sufficiently small audio modulation amplitudes the first derivative of the resonance absorption or dispersion results from the narrow-banding technique. 

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