We see the relevant technical information, it often encounters the concept of dB and dBm. dB, is the decibel, is a ten logarithm of the number concept. Note that the decibel is used only to evaluate a physical quantity and another proportional relationship between the physical quantities, which itself has no physical dimension. The ratio between the amount of each of two 10fold increase, their difference can be expressed as 10 decibels.
For example: A = "100", B = "10", C = "5", D = "1" is
A / D = 20dB; B / D = "10dB"; C / D = "7dB"; B / C = 3dB.
In other words, two poor 10 db is the difference between the amount of 10 times, bad 20 db is 100 times worse, and so on. Usually also need to remember the amount of difference between the two 3 db is twice as bad.
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dBm is a decibel milliwatts meaning. That is, a fixed 1 mW of power of 0dBm, used to determine the system's power. For example, our common reader and the data power mostly 27dBm 30dBm. 27dBm is 500 mW; 30dBm is 1000 mW (1 W). Although only a thin 3dBm, twice as bad as the actual power!
What is the dBi, dBd, dB, dBm, dBc
Q: dBi, dBd, dB, dBm, dBc difference between.
A: They are the power gain of the unit, the difference is as follows:
dBi and dBd is the power gain of the unit, both of which are relative values, but the reference point is not the same. a reference to dBi omnidirectional antenna; dBd reference point for the dipole. DBi and dBd is generally believed that the same gain, the value represented by dBi dBd than that of the larger 2.15 dBi. For example: for a gain of 16 dBd antenna, which converted into units of dBi gain when compared 18.15dBi, generally ignore the decimal places, as 18dBi.
dB power gain of the unit is that a relative value. A calculation of the power when compared to large or small number of B dB, according to the formula 10 lg A / B calculation. For example: A power doubled power than B, then 10 lg A / B = 10 lg 2 = 3dB. In other words, A's power over B, high power 3dB; if the A's power is 46dBm, B's power of 40dBm, you can say, A over B6dB; if A antenna 12dBd, B antenna 14dBd, it can be said A smaller than B 2dB.
dBm is an absolute value of said power unit, is calculated as: 10lg power value / 1mW. For example: If the transmit power of 1mW, according to dBm units after the conversion value should be: 10 lg 1mW/1mW = 0dBm; for 40W of power, then 10 lg (40W/1mW) = 46dBm.
dBc is a relative value of said power unit, and dB is calculated exactly the same. In general, dBc relative to the carrier (Carrier) in terms of power. In many cases, used to measure the relative value of carrier power, as measured interference (cochannel interference, intermodulation interference, crosstalk, with outside interference, etc.) as well as coupling, stray and so the relative value. Place in the use of dBc, in principle, can also use dB instead.
Useful Information  Considerations on the antenna gain and
Practical applications in wireless communications, in order to effectively improve communication effectiveness and reduce the antenna input power, the antenna will be made with the radiation of the structure to focus directional radiated power, which would come out of "antenna gain" concept. Simply put, refers to an antenna gain of the antenna input of RF power to the degree of concentration of radiation, apparently, the antenna gain pattern of relationships with large, the narrower the main lobe, the smaller the antenna side lobe, the higher the gain, and different structures of the antenna, its pattern is a big difference.
In communications technology, power and other considerations, the parameter value equal the same power, antenna gain and also the use of relatively simplified logarithmic law to represent the specific calculation method: a location in a certain direction to produce the same radiation field strength, the loss of nonideal reference antenna input power and antenna input power to be considering taking the logarithm of the ratio multiplied by 10 (G = 10lg (Reference Pin / considerations Pin)), which is called the antenna in the point the direction of the gain. Unit of measure commonly used is dBi antenna gain and dBd. For the dBi, the benchmark for the ideal point source antenna, that is, a true sense of the "point" for the antenna gain compared to baseline. Ideal point source of radiation is omnidirectional antenna, and its pattern is the perfect ball, all point the same sphere of electromagnetic radiation are the same; for dBd, the benchmark was the ideal dipole antenna. Is due to dipole antenna with a directional, so both have a constant difference of 2.15 is fixed 0dBd = "2" .15 dBi.
It should be noted that, commonly referred to as "omnidirectional antenna" is not strictly to say, omnidirectional antenna should refer to the full threedimensional space, but the engineering is often the picture of a plane direction of the circumference of the antenna as omnidirectional antenna, such as whip antennas, it is the main lobe in the radial circle, but there is still axial sidelobes.
Common antenna gain: whip antenna 69dBi, GSM base station with a Yagi antenna 1517dBi, directional parabolic antenna is very easy to do 24dBi.
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