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DB is the abbreviation of decibel, in which the prefix "deci" is the meaning of 1/10. Bel is the inventor of the telephone, the United States surgeon Graham Bell Alexander name in the Bel to remove the last L.

DB that is 1/10 Baer (BEL) - db. DB (DB) is the international unified use of the telecommunications transmission unit, it is not the number of dimensions of the number of units.

DB is equal to 10 times the ratio of the two signal power, which is also equal to 20 times the ratio of the same voltage (assuming two signals to drive the same impedance). Its formula is:

1, 10 LG (a power / B power)

2, 20 LG (a voltage / b)

For example, when a power =2x B power, 10 LG 2 = 3dB, that is, a power greater than B power 3dB.

In the field of telecommunications technology, in order to accurately measure signal in the circuit of the power, voltage and current changes in the transmission case, generally do not directly with watt (W), V (V) and ANN (a) as a unit of measurement, and the use of "level" of such a concept.

The magnitude of a signal is expressed as a power ratio of a reference value, the logarithm of the ratio of the voltage or the current ratio, and is referred to as the "transmission level" ". DB is the transmission level of the unit, known as the "transmission unit". The formula can be expressed as:

D=10lgP1/Po=20lgU1/U0=20lgl1/lo (dB)

DB is also used to describe the signal with respect to a reference level, the reference level is usually defined as 0dB, while the dB value of the signal is 10 times the value of the signal relative to the reference power. Sometimes also added a letter to indicate the reference value, such as the use of 0dBm, dBm = 1mW.

DBm is a value that represents the absolute value of the power (and also can be considered as a ratio of 1mW power), the formula is: 10log (power value /1mw).

[example] if the power P for 1MW, converted to 0dBm after dBm.

For 40W power, according to the value of the dBm unit should be converted to:

10log (40W/1mw) =10log (40000) =10log4+10log10000=46dBm.

DBi and dBd are the amount of antenna power gain, both of which are a relative value, but the reference is not the same. DBi reference for the full directional antenna, dBd reference for the dipole, so a slight difference between the two. It is generally believed that the same gain, expressed with dBd than with dBi said to be large

For an antenna with a gain of 16dBd, the gain is converted to a unit of dBi, while the 18.15dBi (generally ignores small digits, 18dBi).

[example] 0dBd=2.15dBi.

DBc is also a unit of the relative value of the power, which is exactly the same as the calculation method of dB. Generally speaking, DBC is relative to the carrier (carrier) power, in many cases, used to measure and carrier power relative value, used, for example, a measure of the relative amount of interference (co channel interference, intermodulation interference, intermodulation interference, out of band interference) and coupling, spurs. In the use of dBc place, in principle, can also be used as a substitute for dB.

Like dBm and dBw, dBw is a unit (which can also be considered as a reference to 1W power). The formula is: 10log (power value /1w). The conversion between dBw and dBm is: 0 dBw = W = 10log1000 = MW 10log1 = 30 dBm.

[example] if the power P for 1W, converted to 0dBw after dBw.

In short, DB, the DBI and DBD, DBC is the ratio between the two quantities, the relative size between the two quantities, and DB is the ratio between the two quantities, the relative size between the two quantities, said the DBM is expressed as the value of the absolute size of power; DBM, dBw is expressed as the value of the absolute size of power. In dB, dBm, dBw calculation, it is essential to pay attention to the basic concept, with a dBm (or dBw) minus another dBm (dBw), the results obtained are dB, such as: 0dBm - 30dBm = 30dB.

Generally speaking, in engineering, dBm (or dBw) and dBm (or dBw) not only between the addition and subtraction, multiplication and division. And the most used is the subtraction: DBM DBM subtraction is actually dividing two power, signal power and noise power dividing is the signal to noise ratio (SNR). DBm plus dBm is actually the two power multiplication.

Teach you how to distinguish between dBm, dB, dBi, dBd, dBm or dbm.

Power unit and P (Watt) conversion formula:

(10*P) dBm= (10*P) dB-30dB (P: w)

First, DB is a pure counting unit: for power, dB = 10*lg (A/B). For the voltage or current, DB = 20*lg (A / b).DB actually again simple but the, is to a great (followed by a long string of 0), or very small (in front of a bunch of zeros) the number of relatively briefly expressed. Such as:

X=1000000000000000 (how many?)

10lgX=150dB

X=0.000000000000001

DB 10lgX=-150

DBm is defined as miliwatt. 0 dBm=10lg1mw;

DBw definition watt. 0 dBw = W 10lg1000 = MW 10lg1 = 30 dBm.

DB always defines the power unit in the default case, and the 10lg is the. Of course, in some cases, the signal intensity (Amplitude) can be used to describe the work and power, this time with the 20lg as a meter. Whether it is in the field of control or signal processing is the way. For example, sometimes we can see the expression of dBmV.

In dBm, dB calculation, to pay attention to the basic concept. For example, said in front of 0dBw = 10lg1W = 10lg1000mw = 30dBm; and, for example, with a dBm minus another dBm, the results obtained are dB. Such as: 0dBm - 30dBm = 30dB.

Generally speaking, in engineering, between dB and dB not only addition and subtraction, multiplication and division. And the most used is the subtraction: DBM DBM subtraction is actually dividing two power, signal power and noise power dividing is the signal to noise ratio (SNR). DBm plus dBm is actually the two power multiplication, this is not much (I only know that in the power spectrum convolution calculation has such an application). DBm by dBm is what, 1mW 1mW Times Square? In addition to the classmates old wrote me such almost and Goldbach conjecture to keep pace with the expression, I live for so many years did not seen any engineering field to play this.

DB is the unit of the power gain, representing a relative value. When calculating the power of A compared to B large or small number of dB, can be calculated by the formula 10 A/B lg. For example: A power than B power twice, then 10 A/B LG = 10 LG 2 = 3dB. That is, the power of A than B power big 3dB; if the power of 46dBm for B, A power of 40dBm, you can say, A than B big 6dB; if the A antenna for B, antenna for 14dBd, can say A than B small 2dB 12dBd.

DBm is a unit that represents the absolute value of the power, and the formula is: 10lg power value /1mW. For example: if the transmission power is 1mW, according to the dBm unit after the conversion value should be: 10 1mW/1mW LG = 0dBm; for the power of 40W, then 10 =46dBm (40W/1mW) lg.

1, dBm

DBm is an absolute value of the absolute value of the test power, the formula is: 10lg (power value /1mw).

[example 1] if the transmission power of P is 1MW, converted to 0dBm after dBm.

2] for the 40W power, according to the value of dBm units should be converted to:

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

2, dBi and dBd

DBi and dBd are the values of the test intrinsic gain (power gain), both of which are a relative value,

But the reference is not the same. DBi reference for the full directional antenna, dBd reference for the dipole,

So they are slightly different. It is generally believed that the same gain, expressed by dBi than with dBd

Come to big 2.15.

[example of 3] for a gain of 16dBd antenna, the gain is converted into a unit of dBi, the 18.15dBi

(generally ignore small digits, 18dBi).

[example 0dBd=2.15dBi 4].

[example GSM900 5] antenna gain can be 13dBd (15dBi), GSM1800 antenna gain can be

15dBd (17dBi).

3, dB

DB is a characterization of the relative value of the value, when considering the power of a B power compared to the number of large or small dB,

According to the following formula: 10lg (a power / B power)

A 6] a power is twice larger than B power, then 10lg (a power / B power) =10lg2=3dB.

That is to say, the power of a power is greater than the power of 3 dB.

Example 7/8 7] inch GSM900 feeder 100 meters transmission loss is about 3.9dB.

8] if a power of 46dBm, B power of 40dBm, it can be said that a greater than 6 dB.

If a 9] antenna for 12dBd, B antenna for 14dBd, can be said a smaller than 2 dB.

4, dBc

Sometimes it will also see the dBc, it is also a value of the relative value of the unit, and dB calculation method is exactly the same.

Generally speaking, dBc is relative to the carrier (Carrier) power, in many cases, used to measure the

The relative value of carrier power, such as the measure of interference (same frequency interference, intermodulation interference, intermodulation interference, band interference etc.)

And the relative value of the coupling and the stray.

In the use of dBc place, in principle, can also be used as a substitute for dB.

Empirical algorithm:

There is a simple formula: 0dBm=0.001W plus 10= on the left side of the by 10

So 0+10dBM=0.001*10W is 10DBM=0.01W

So get 30DBM=1W 40dBM=10W 20DBM=0.1W

The left and right by 2 plus 3=, such as 40+3dBM=10*2W, 43dBm=20W, which is just fine with the experience formula.

So -50dBm=0dBm-10-10-10-10-10=1mW/10/10/10/10/10=0.00001mW.

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