| 1. Conversion of power unit mW and DBM The RF signal output by the radio transmitter is transmitted to the antenna through a feeder (Cable), which emits electromagnetic waves. After the electromagnetic wave arrives at the receiving location, it is received by the antenna (only a small portion of the power is received) and sent to the radio receiver through a feeder. Therefore, in the wireless network project, it is very important to calculate the transmit power of the transmitter and the radiation capability of the antenna. TX is short for transmitting (transmits. The transmit power of radio waves refers to the energy in a given frequency range. there are usually two measurements: 1. Power (W): a linear level relative to Watts. For example, the transmit power of a Wi-Fi network card is usually 0.036, or 36 mW.
2. Gain (DBM): proportional level relative to 1 milliwatt (milliwatt. For example, the transmit gain of a Wi-Fi network adapter is 15.56dbm. The two expressions can be converted to each other:
1. DBM = 10 x log [Power MW]
2. Mw = 10 [gain DBM/10 dBm] in a wireless system, an antenna is used to convert current waves into electromagnetic waves. During the conversion process, it can also "zoom in" The transmitted and received signals ", the measurement of this type of energy amplification is "gain (GAIN )". The antenna gain is measured in DBI ". Because the electromagnetic wave energy in the wireless system is produced by the emission energy of the transmitting device and the amplification and superposition of the antenna, it is best to measure the emission energy with the same measurement-gain (DB), for example, the transmit device power is 100 MW or 20 dBm. If the antenna gain is 10dbi, then:
total emission energy = transmit power (DBM) + antenna gain (DBI)
= 20dbm + 10dbi = 30dbm
or: = 1000 MW = 1 W
in a" low-power "system (such as a wireless local area network device), each database is very important, remember the "3 dB rule ". Each increase or decrease of 3 dB means doubling or reducing the power by half:
-3 dB = 1/2 power
-6 dB = 1/4 power
+ 3 dB = 2x power
+ 6 dB = 4x power
example, 100 MW wireless transmit power is 20 dBm, 50 MW wireless transmit power is 17dbm, and 200 MW transmit power is 23dbm.
power/level (DBM): the output capacity of the amplifier, generally measured in W, MW, and DBM. DBM is the absolute power level expressed in decibels with 1 MW as the reference value. Conversion formula:
Level (DBM) = 10lgw
5 W → 10lg5000 = 37dbm
10 W → 10lg10000 = 40dbm
20 W → 10lg20000 = 43dbm It is not difficult to see that each time the power is doubled, the level value increases by 3 dBm.
2. What are the meanings and differences between dBm, DBI, DBD, DB, and DBC? Computation may occur in many examples of Professional Books, and the significance of many computation results may confuse us. I have encountered such a problem and wonder if the Taoist School is influenced by DBM, DBI, DBD, DB, I am confused about the meaning of these terms of DBC. I would like to give a brief introduction to my understanding here. 1. DBM
DBM is a volume that represents the absolute power value. 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 represent the amount of gain (power gain), both of which are relative values, but the reference benchmark is 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 represented by DBI, Which is 2.15 larger than that expressed by 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 volume that represents relative values. When considering the number of DB whose power is larger or smaller than that of B, 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, if the power of a is 3 dB higher than that of B, the power is doubled.
[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. |
