One manifestation of the classic dipole antenna has a gain factor of about 1.64 (or 10*log(1.64/1) = 2.15 dB) over an isotropic radiator. The nature of the decibel is such that instead of multiplying linear values of gain you can, instead, add logarithmic values of gain. One tenth was deemed a handy value in the 1930s so decibel has been the go to unit for logarithmic voltage and power gain representation since. making decibel, centibel, millibel, microbel, etc. SI fractional prefixes include deci, centi, milli, micro, etc. The bel is rather large in scope prompting the popularity of adding an SI prefix to create a smaller, more pragmatic unit. The bel and neper have the following relationship… The shorthand identifier for bel and neper are B and Np respectively. There is a similar unit called the neper where one neper is the change in the level of a field quantity when the field quantity changes by a factor of e, that is 1 Np = ln(e) = 1. In honor of Alexander Graham Bell, the unit bel represents the base 10 logarithm of a ratio between two power quantities of 10:1. …or about twice the power radiated towards the horizon. Gain of Diamond CP22E over dipole = 3.16 / 1.64 = 1.93 If you want to know the gain of the CP22E over a dipole you can simply divide one by the other… The Diamond CP22E of figure 1b has a gain factor of about 3.16 over an isotropic radiator. For example the classic dipole has a gain factor of about 1.64 over an isotropic radiator with is gain factor of exactly 1.00. One can easily get by handling antenna gain using only multiplication. Figure 1b shows a Diamond CP22E antenna revealing how the power intensity is taken from some directions and added towards the waistline. This is impossible to achieve with any practical antenna, but because it is based on a solid definition, it is unwavering as a reference. Looking at figure 1a above we see radiation of power equally in all directions. Isotropic referenceĪ key feature of the professional antenna community is the reliance on the isotropic radiator, itself based on the very definition of directivity, as the rock solid reference from which we measure all antennas. There is a difference between Directivity and Gain, but for the remainder of this article I will assume antenna efficiency is perfect and assume they are the same. 1 – Learn about antenna directivity and gain here ![]() I’ve gathered together some details discussing the definitions of Directivity and Gain and placed it in a new technical topic portion of this web site always available on the right sidebar… Fig. Let’s step our way though the topic and see what we can learn from the pros. Fortunately the established antenna community has things well in hand. The problem centers around the notion of what reference to use so that everyone is on the same channel. Everyone understands the general idea, but when decibels enter the picture we have trouble. A relatively simple concept, antenna gain has proven to be problematic in certain circles of the radio world with a few distinct groups: antenna professionals, antenna aficionados and most everyone else.
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