Calculation of Intermodulation from a Single Carrier Amplitude Characteristic

The intermodulation analysis presented in this paper is based on the important observation that any output component of a memoryless nonlinear device can be expressed as an integral of the product of two functions, one being the single carrier amplitude characteristic of the nonlinear device and the other being a function of the statistical parameters of the input signal. The analysis can also be extended to nonlinear devices with AM-PM conversion by expressing the amplitude characteristic as a complex function. The signal-dependent function is given analytically for two simple but important types of signals, for two sinusoidal carriers of equal level, and for Gaussian noise, and it is demonstrated that good agreement has been obtained when the method has been applied to microwave devices like high powerX-band klystrons and traveling wave tubes. It is also shown that the method is convenient for analysis of intermodulation in cascaded nonlinear elements for which the individual single carrier amplitude characteristics are known.     

Large/small carrier performance of non-linear devices

The intermodulation properties of a memoryless non-linear amplifier with two carriers having large level difference are in the limit determined by the properties of the amplitude characteristic of the amplifier at a single point, i.e. at the operating point determined by the stronger carrier. The paper derives the mathematical expression for the level of the dominating third-order intermodulation product, and also shows how this level can be determined graphically from a given amplitude characteristic.     

Performance and wake of a Savonius vertical‐axis wind turbine under different incoming conditions

In this study, the performance, drag, and horizontal midplane wake characteristics of a vertical‐axis Savonius wind turbine are investigated experimentally. The turbine is drag driven and has a helical configuration, with the top rotated 180° relative to the bottom. Both performance and wake measurements were conducted in four different inflow conditions, using Reynolds numbers of Re_D≈1.6×10⁵ and Re_D≈2.7×10⁵ and turbulence intensities of 0.6% and 5.7%. The efficiency of the turbine was found to be highly dependent on the Reynolds number of the incoming flow. In the high Reynolds number flow case, the efficiency was shown to be considerably higher, compared with the lower Reynolds number case. Increasing the incoming turbulence intensity was found to mitigate the Reynolds number effects. The drag of the turbine was shown to be independent of the turbine's rotational speed over the range tested, and it was slightly lower when the inflow turbulence was increased. The wake was captured for the described inflow conditions in both optimal and suboptimal operating conditions by varying the rotational speed of the turbine. The wake was found to be asymmetrical and deflected to the side where the blade moves opposite to the wind. The largest region of high turbulent kinetic energy was on the side where the blade is moving in the same direction as the wind. Based on the findings from the wake measurements, some recommendations on where to place supplementary turbines are made.     

Intelligible Crosstalk in Nonlinear Amplifiers: Calculation of AM-PM Transfer

This concise paper analyzes the transfer of amplitude modulation from one sinusoidal carrier to phase modulation of other carriers passing through the same memoryless nonlinear device. It gives exact expressions for the AM-PM transfer coefficient, which is one part of the mechanism that leads to intelligible crosstalk, and the expressions are valid for sinusoidal carriers in the presence of Gaussian noise through devices with known amplitude and phase characteristic. Two particular input signal combinations (two carriers with a given level difference, and a large number of small carriers) are considered in more detail, and the expressions are applied to a typical TWT characteristic.