Half-power point

Maximum continuous speed, 105 percent = Initial (lesser) speed at. 707 x peak amplitude (critical) Wg = Final (greater) speed at.707 x peak amplitude (critical) W2-/v,= Peak width at the half-power" point... 

As illustrated in Figure 44.42, a resonance peak represents a large amount of energy. This energy is the result of both the amplitude of the peak and the broad area under the peak. This combination of high peak amplitude and broad-based energy content is typical of most resonance problems. The damping system associated with a resonance frequency is indicated by the sharpness or width of the response curve, ci) , when measured at the half-power point. i MAX is the maximum resonance and Rmax/V is the half-power point for a typical resonance-response curve. 

For optical depth t 1 the observed interstellar molecular lines usually have a gaussian shape. This is to be expected, since collisional broadening, which causes the Lorentzian line profile, should be negligible and become important only at gas densities 1012 — 1014 cm- 3. If thermal motions of the molecules were the only source of line broadening the line half power width (i.e. the width between half power points) would be given by... 

Pulse amplifiers with gain greater than 6 decibels and with a baseband bandwidth greater than 500 megahertz (having the low frequency half-power point at less than... 

MHz and the high frequency half-power point at less than 1 MHz and the high frequency half-power point greater than 500 MHz) and output voltage greater than... 

The quality factor of an oscillation is defined by Q = yntlk with y being the damping coefficient. If the damping is small the Q factor equals the quotient of the eigenfrequency of the free cantilever and the width of the resonance maximum at the so-called half power point (HPP) (where the amplitude has decayed to Ahpp = A max /v ) G = ci>Q /AtwHPP- In air the Q factors are typically between 100 and 1000. In UHV they are approximately 1(X) times larger. 

The output waveform of a stable, single-frequency laser far above the threshold of oscillation may be approximated by an almost perfect sine wave with nearly constant amplitude and frequency. For a laser operating in an ideal environment, the spectral purity is measured by a linewidth which is determined by frequency fluctuations caused by random walk of the oscillation phase under the Influence of spontaneous emission (quantum) noise. In their fundamental 1958 paper, Schawlow and Townes predicted that the quantum phase noise limited line profile will be a Lorentzian with a full width between the half power points (FVIHM) that may be approximated by ... 

Strictly speaking, antenna bandwidth is the difference in frequency between two points at which the power output of the transmitter drops to one-half the midrange value. The points are called half-power points. A half-power point is equal to a VSWR of 5.83 1, or the point at which the voltage response drops... 

The points on the pattern where the field strength is 70% of the maximum are known as the half-power points, and the angular separation of these points is the beam width. The gain of the antenna is increased by narrowing the beam width to concentrate the radiated power in the desired directions, and the product of the gain and beam width tends to be constant... 

Antenna beamwidth The angle between the half-power points (3 dB points) of the main lobe of the antenna pattern when referenced to the peak power point of the antenna pattern. Antenna beamwidth is measured in degrees and normally refers to the horizontal radiation pattern. 

Half-power point, 122 Half-wave rectifier, 155 Harmonics, 142, 182 Haywire circuits, 62 footnote Hearing, human, 44, 121 Heat, 61, 101, 212, 236 effect onR, 147, 150 sink, 160, 174 Henry, 113 hfe, 172... 

Frequently the cutoff or half-power points are described in terms of decibel (db) units rather than voltage units. The conversion is... 

Thus the half-power points are called 3-db points, that is, signal level is 3 db down from the maximum level. The bandwidth defined by the halfpower points is then the 3-db BW. 

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