What does DB and DBM mean ~

DBM
Power Unit and P (Watt) conversion formula:
DBM = 30 + 10lgp (P: Tile)

First, DB is a pure counting unit: DB = 10 logX. The significance of DB is actually a simple one, that is
The number of large (followed by a long string of 0) or small (followed by a long string of 0) is briefly expressed. For example:


X = 1000000000000000 (How many ?) = 10 logX = 150 dB

X = 0.000000000000001 = 10 logX =-150 dB

DBM defines miliwatt. 0 dBm = 10log1 MW;
Dbw defines Watt. 0 dbw = 10log1 W = 10log1000 Mw = 30 dBm.

By default, the DB always defines the power unit, measured in 10 logs. Of course, in some cases, the signal strength (
Mplitude) to describe the power and power. At this time, 20log is used. Both the control field and the signal processing field
This is the case. For example, sometimes you can see the expression of dbmv.

Pay attention to the basic concepts in dB and DBM computing. For example, the preceding 0dbw = 10log1w = 10log1000mw = 3
0 dBm; for example, when one DBM is used to subtract another dBm, the result is dB. For example: 30dbm-0dbm = 30
DB.

In general, there is only addition and subtraction between DB and DB in the project, without multiplication and division. The most commonly used method is subtraction: dBm minus D.
In fact, BM is divided by two power sources. signal power and noise power are divided by signal-to-noise ratio (SNR ). DBM + dBm
It is a multiplication of two power values. This is rare (I only know that this is an Application in Power Spectral convolution ).
What is dBm multiplied by DBM? 1 MW is the power of 1 MW? Except for the old classmates who wrote this to me, it was almost possible to guess about it
I have never seen any engineering field play this role after I have been living for so many years.


DB is the unit of power gain, indicating a relative value. When calculating the number of DB whose power is larger or smaller than that of B, you can press
Formula 10: lg a/B. For example, if a power is twice the power of B, 10 lg a/B = 10 LG 2 = 3 dB. Also
That is to say, a's power is 3 dB higher than B's power. If a's power is 46dbm and B's power is 40dbm, it can be said that
6 dB larger than B. If antenna A is 12dbd and antenna B is 14dbd, A is 2 dB smaller than antenna B.

DBM is a unit that represents the absolute power value. The formula is: 10lg power value/1 MW. For example, if the transmit power is
1 MW, converted in dBm units, the value should be: 10 LG 1 MW/1 MW = 0dbm; for 40 W power, 10 lg (
40 W/1 MW) = 46dbm.



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,
However, 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 represented by DBI.
To be larger than 2. 15.


[Example 3] For an antenna with a gain of 16 DBD, the gain is 18.15dbi when the unit is DBI.
(Generally, decimal places are 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 relative values. When considering the number of DB whose power is larger or smaller than that of B,
The formula is as follows: 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, for example, used to measure interference (same frequency interference, Intermodulation Interference, Intermodulation Interference, out-of-band interference, etc)

And the relative values of coupling and stray.
In principle, database can also be used to replace DBC.



DBm, DBI, DBD, DB, and DBC, which are frequently used for wireless communication.
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. DBI
The reference is a full-direction antenna, and the reference of DBD is a dipole, so the two are slightly different. Table
Shows the same gain, expressed in DBI is greater than expressed in DBD 2. 15.
[Example 3] For an antenna with a gain of 16 DBD, the gain is converted into a unit of DBI, Which is 18.15dbi (
Decimal point, 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 the number of DB whose power is larger or smaller than the power of B, calculate as follows:
Formula: 10lg (A/B)
[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 is 3 dB higher than the power 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. Generally
In contrast to the carrier power, DBC is used to measure the relative power of the carrier in many cases.
Value, for example, used to measure 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.

Empirical algorithms:
There is a simple formula: 0dbm = 0.001 W plus 10 on the Left = 10 on the right
So 0 + 10dBm = 0.001*10 W, that is, 10dBm = 0.01 W
Therefore, 20dbm = 0.1 W 30dbm = 1 W 40dbm = 10 W
Plus 3 = 2 on the left side, for example, 40 + 3dbm = 10*2 w, that is, 43dbm = 20 W. These are empirical formulas that are quite useful.

Therefore,-50dbm = 0dbm-10-10-10-10-10 = 1 MW/10/10/10/10/10 = 0.00001 mW.