1.
Frequency
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Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as frequency, which emphasizes the contrast to spatial frequency. The period is the duration of time of one cycle in a repeating event, for example, if a newborn babys heart beats at a frequency of 120 times a minute, its period—the time interval between beats—is half a second. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as vibrations, audio signals, radio waves. For cyclical processes, such as rotation, oscillations, or waves, in physics and engineering disciplines, such as optics, acoustics, and radio, frequency is usually denoted by a Latin letter f or by the Greek letter ν or ν. For a simple motion, the relation between the frequency and the period T is given by f =1 T. The SI unit of frequency is the hertz, named after the German physicist Heinrich Hertz, a previous name for this unit was cycles per second. The SI unit for period is the second, a traditional unit of measure used with rotating mechanical devices is revolutions per minute, abbreviated r/min or rpm. As a matter of convenience, longer and slower waves, such as ocean surface waves, short and fast waves, like audio and radio, are usually described by their frequency instead of period. Spatial frequency is analogous to temporal frequency, but the axis is replaced by one or more spatial displacement axes. Y = sin = sin d θ d x = k Wavenumber, in the case of more than one spatial dimension, wavenumber is a vector quantity. For periodic waves in nondispersive media, frequency has a relationship to the wavelength. Even in dispersive media, the frequency f of a wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave. In the special case of electromagnetic waves moving through a vacuum, then v = c, where c is the speed of light in a vacuum, and this expression becomes, f = c λ. When waves from a monochrome source travel from one medium to another, their remains the same—only their wavelength. For example, if 71 events occur within 15 seconds the frequency is, the latter method introduces a random error into the count of between zero and one count, so on average half a count. This is called gating error and causes an error in the calculated frequency of Δf = 1/, or a fractional error of Δf / f = 1/ where Tm is the timing interval. This error decreases with frequency, so it is a problem at low frequencies where the number of counts N is small, an older method of measuring the frequency of rotating or vibrating objects is to use a stroboscope

2.
Effective radiated power
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Effective radiated power, synonymous with equivalent radiated power, is an IEEE standardized definition of directional radio frequency power transmitted from a theoretical half-wave dipole antenna. It is differentiated from effective isotropic radiated power mainly by use of antenna gain instead of absolute gain in the calculation. The term antenna gain is assumed to be absolute unless specifically stated to be relative, the gain is then multiplied by the power actually accepted by the antenna to result in the actual ERP value. Power losses which occur prior to the antenna, e. g. in the line or from inefficiency in the generator itself are therefore not included in the calculation of ERP or EIRP. Antenna gain is closely related to directivity and often used interchangeably. However, gain is less than directivity by a factor called radiation efficiency. Whereas directivity is entirely a function of wavelength and the geometry and type of antenna, specifically, accelerating charge causes electromagnetic radiation per Maxwells equations. Therefore, antennas use a current distribution on radiating elements to generate electromagnetic energy that propagates away from the antenna and this coupling is never 100% efficient, and therefore antenna gain will always be less than directivity by this efficiency factor. The receiver would not be able to determine a difference, maximum directivity of an ideal half-wave dipole is a constant, i. e.0 dBd =2.15 dBi. Therefore, ERP is always 2.15 dB less than EIRP, the ideal dipole antenna could be further replaced by an isotropic radiator, and the receiver cannot know the difference so long as the input power is increased by 2.15 dB. Unfortunately, the distinction between dBd and dBi is often left unstated and the reader is forced to infer which was used. For example, a Yagi-Uda antenna is constructed from several dipoles arranged at intervals to create better energy focusing than a simple dipole. Since it is constructed from dipoles, often its antenna gain is expressed in dBd, obviously this ambiguity is undesirable with respect to engineering specifications. A Yagi-Uda antennas maximum directivity is 8.77 dBd =10.92 dBi and its gain necessarily must be less than this by the factor η, which must be negative in units of dB. Neither ERP nor EIRP can be calculated without knowledge of the power accepted by the antenna, let us assume a 100 Watt transmitter with losses of 6 dB prior to the antenna. ERP <22. 77dBW and EIRP <24. 92dBW, polarization has not been taken into account so far, but properly it must be. When considering the dipole radiator previously we assumed that it was aligned with the receiver. Now assume, however, that the antenna is circularly polarized