dBm, dBi, dBd, dB, dBc Interpretation

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1, dBm
dBm is a power of absolute value sign test is calculated as: 10lgP (power value / 1mw).
[Example 1] If the transmission power P is 1mw, converted into dBm after 0dBm.
[Example 2] for 40W of power, according to the dBm value of units after conversion should be:
10lg (40W/1mw) = 10lg (40000) = 10lg4 +10 lg10 +10 lg1000 = 46dBm.
2, dBi and dBd
dBi and dBd is the gain value of test characteristics (power gain), both of which are a relative value, but not the same reference point. a reference to dBi omni-directional antenna, dBd reference point for the dipole, so the two are slightly different. Generally believed that the same gain, represented by dBi dBd than that out to a large 2.15.
[Example 3] For the side of the antenna gain of 16dBd its converted into units of dBi gain when compared 18.15dBi (generally ignore decimal places, as 18dBi).
[Example 4] 0dBd = 2.15dBi.
[Example 5] GSM900 antenna gain can 13dBd (15dBi), GSM1800 antenna gain can 15dBd (17dBi).
3, dB
dB is a characterization of the relative value of the value, when considering the power compared to a B or a small number of large power dB, according to the following formula: 10lg (A power / B power)
[Example 6] A B power than double the power, then 10lg (A power / B power) = 10lg2 = 3dB. In other words, a power larger than the B power 3 dB.
[Example 7] 7 / 8 inches GSM900 feeder transmission loss of about 100 meters of 3.9dB.
[Example 8] If a power is 46dBm, B's power of 40dBm, it can be said that a large B than 6 dB.
[Example 9] If a antenna 12dBd, B antenna 14dBd, B can be a little more than 2 dB.
4, dBc
Sometimes see dBc, it is also 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 the carrier power, such as used to measure interference (co-channel 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.

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Experience algorithm:
There is a simple formula: 0dbm = 0.001w to the left of the right by 10 = 10
Therefore, 0 +10 DBM = 0.001 * 10W that 10DBM = 0.01W
It may therefore 20DBM = 0.1W 30DBM = 1W 40DBM = 10W
There to the left of the right by 3 = 2, such as 40 +3 DBM = 10 * 2W, which 43DBM = 20W, which is the empirical formula, fine used.
So-50DBM = 0DBM-10-10-10-10-10 = 1mw/10/10/10/10/10 = 0.00001mw.

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