Analysis of DBM and DB concepts

1. DBM

DBM is the absolute value of power. The formula is: 10lgp (power value/1 MW ).

[Example 1] If the transmit power P is 1 MW, it is converted to dBm and then 0dbm.

[Example 2] for 40 W power, the converted value in dBm unit should be:

10lg (40 W/1 MW) = 10lg (40000) = 10lg4 + 10lg10 + 10lg1000 = 46dbm.

2. DBI and DBD

DBI and DBD are the obtained Gain values (power gain). Both are relative values, but the reference standards are different. The reference of DBI is a full-direction antenna, and the reference of DBD is a dipole, so the two are slightly different. It is generally considered that the same gain is expressed in DBI, which is 2. 15 larger than that expressed in DBD.

[Example 3] For an antenna with a gain of 16 DBD, the gain is converted to 18.15dbi (decimal places are generally ignored, which is 18dbi ).

[Example 4] 0dbd = 2.15dbi.

[Example 5] the gain of the GSM900 antenna can be 13dbd (15dbi), and the gain of the GSM1800 antenna can be 15dbd (17dbi ).

3. DB

DB is a value that represents the relative value. When considering how many DBs with a power greater or smaller than B's power, the following formula is used: 10lg (a power/B power)

[Example 6] If the power of a is twice the power of B, then 10lg (the power of a/B) = 10lg2 = 3 dB. That is to say, the power of a is 3 dB higher than that of B.

[Example 7] 8 inch M transmission loss of the 100/GSM 900 feeder is about dB.

[Example 8] If the power of a is 46dbm and that of B is 40dbm, it can be said that a is 6 dB larger than that of B.

[Example 9] If antenna A is 12dbd and antenna B is 14dbd, it can be said that antenna A is 2 dB less than antenna B.

4. DBC

Sometimes we can see that DBC, which is also a unit that represents the relative power value, is exactly the same as the DB calculation method. In general, DBC is used to measure the relative value of the carrier power in many cases relative to the carrier power, for example, it is used to measure the relative values of Interference (same-frequency interference, Intermodulation Interference, Intermodulation Interference, out-of-band interference, etc.) and coupling and stray. In principle, database can also be used to replace DBC.