Hello!
This post refers to an introduction to dB/dBm/dBi/dBd/EIRP. Please see more details below.
DB
DB: decibel. It is a pure unit of counting and its formula is:
DB = 10lg (A/B), where A and B represent power.
DB = 20lg (A/B), where A and B represent voltage or current.
DB represents the relative value of two powers, voltages or currents.
For example, if the power of A is 10000W and that of B is 1000W, then 10lg (10000/1000) = 1dB means that A is 1dB larger than B.
DBm
DBm is decibel milliwatt, which represents the absolute value of power. It can be converted to power unit W. The formula is: 10lg (power value / 1mW).
For example, the maximum transmitting power of AP6610DN 2.4 RF is 1W. The converted value in dBm units should be 10lg (1W/1mW)= 10lg1000 = 30dBm.
DB
DB is the ratio between two quantities, representing the relative size between two quantities, while dBm is the absolute value of power. In the calculation of dB and dBm, dBm minus dBm is actually the division of two powers, and the result is dB.
For example, if the power of A is 30 dBm and that of B is 0 dBm, then A is 30 dBm - 0 dBm larger than B = 10 lg1000 mW - 10 LG1 mW = 30 dB.
DBi/dBd
Both dBi and dBd are units representing power gain, both of which are relative values, but their reference benchmarks are different.
dBi: The radiation in all directions is uniform relative to the power gain of the point source antenna.
dBd: Power gain relative to the array antenna.
It is generally believed that dBi represents the same gain, which is 2.15 larger than dBd. For example, for an antenna with a gain of 16 dBd, when the gain is converted to dBi, it is 18.15 dBi.
In wireless LAN, dB is mainly used as the unit of signal-to-noise ratio and loss; dBm is mainly used as the unit of radio frequency transmission, receiving power and radio frequency noise; dBi and dBd are mainly used as the unit of antenna gain.
EIRP
Effective Isotropic Radiated Power (EIRP) is the product of the antenna power PT supplied to the radio transmitter and the antenna absolute gain GT in a given direction.
The formula for calculating EIRP is:
EIRP = P - Loss + G
P: The output power of the transmitter is dBm.
Loss: Feed loss between transmitter output and antenna feed in dB.
G: The transmission gain of the antenna in dBi.
In WLAN, EIRP is usually used to measure the intensity of interference and the ability of transmitter to transmit strong signals. Therefore, EIRP calculation is often used, which involves the above units.
For example, the output power of a device is 20 dBm, the antenna gain is 30 dBi, and the feed loss is 2 dB. Then, EIRP = 20dBm + 30dBi) - 2dB = 48dBm.
That's all for this post about an introduction to dB / dBm / dBi / dBd / EIRP. If you have questions about this, kindly let us know! Thanks!
