Bell (B)
Bell (B) the ratio of the volume originally used with a power of 10 indicates, Alexander Graham Bell's name. Thus, 1B represents a power ratio of 10: 1, which is a logarithm of base-10,100: 1 = 2B, 1000: 1 = 3B. Mathematical relationship: LG (P2 / P1) , where P2 / P1 represents a power ratio. It can be seen Bell a larger unit, so inconvenient to use, usually with smaller units: decibel (dB), d represents "one (deci -) out", 1B = 10dB, 2B = 20dB,
DB decibel is a pure counting unit , also the power gain of the unit. It is to a large (followed by a long string of 0's) or small (preceded by a long string of 0's) number of relatively brief that out. Such as:
Example: X = 1000000000000000 (total 15 0) → 10lgX = 150dB
Example: X = 0.000000000000001 (total 15 0) → 10lgX = -150 dB
dB, represents a relative value. When calculating A power large or small compared to the number of B dB, according to the formula 10 lg A / B calculation.
For example: A B power twice as large as the power, then 10 lg A / B = 10 lg 2 = 3dB. That is, the ratio of the power A of the high power 3dB B; if A is a power of 46dBm, 40dBm power is B, it can be said, A large 6dB than B; if A is an antenna 12dBd, B antenna 14dBd, it can be said A 2dB less than B. Generally speaking, in engineering, dB and dB is only between addition and subtraction, multiplication and division no.
dB default is always the definition of power units to 10lg the count. Of course, in some cases it may be the signal intensity (Amplitude) to describe and reactive power, this time with the count 20lg. Whether or control signal processing field like this. For example, sometimes you can see the expression dBmV.
dBm is defined miliwatt . with respect to the reference power in dBm 1 milliwatt (mW) of power decibel value.
30dBmW = = = 1000mW 1W 0 dBW 0 dBm = 10lg1mw;
dBm is a unit represented by absolute power, is calculated as: 10lg power value / 1mW.
For example: if the transmit power of 1mW, a value obtained by the conversion performed in dBm should be: 10 lg 1mW / 1mW = 0dBm; 40W for power, then 10 lg 46dBm (40W / 1mW) =.
dBm most used subtraction: dBm reduction is actually two power divided dBm, signal power and noise power is divided signal to noise ratio (SNR).
dBw 定义watt。0 dBw = 10lg1 W = 10lg1000 mw = 30 dBm。
In dB, dBm calculation, pay attention to basic concepts. Such as the previously said 0dBw = 10lg1W = 10lg1000mw = 30dBm;
As another example, when a further reduction by a dBm dBm, the result is dB. Such as: 30dBm - 0dBm = 30dB.
. 1, dBm
dBm is a value intrinsic to test the absolute power, is calculated as: 10lg (power value / 1mw).
[Example 1] If the transmit power P is 1mw, it is converted in dBm after 0dBm.
[Example 2] For power 40W, the value is converted according to dBm units shall: 10lg (40W / 1mw) = 10lg (40000) = 10lg (4 * 10 ^ 4) = 40 + 10 * lg4 = 46dBm.
2, dBi and dBd
dBi and dBd test are intrinsic gain value (power gain), both of which are a relative value, but not the same as the reference datum. Reference dBi omnidirectional antenna for the reference, the reference datum dBd dipole, so the two slightly different. Generally believed that mean the same gain, represented by dBi dBd than that out with a larger 2.15.
[Example 3] For 16dBd side antenna gain, its gain is converted into units of dBi when compared 18.15dBi (generally ignore decimal places, as 18dBi).
[Example 4] 0dBd = 2.15dBi.
[Example 5] GSM900 antenna gain may 13dBd (15dBi), GSM1800 antenna gain may 15dBd (17dBi). . 3, dB
dB is a value characterizing the relative value, when considering the power compared to acetate A power large or small number of dB, is calculated according to the following formula: 10lg (A power / B power)
[Example 6] A power ratio b power doubled, then 10lg (A power / b power) = 10lg2 = 3dB. In other words, A's power than the power of the big B 3 dB.
[Example 7] 100 m feeder GSM900 transmission loss of about 7/8 inch 3.9dB.
[Example 8] A if the power is 46dBm, 40dBm power of the acetate, it can be said, than B A large 6 dB.
[Example 9] A If the antenna is 12dBd, antenna B 14dBd, say A smaller than B 2 dB. 4, dBc
Sometimes see dBc, it is also a representation of the relative value of the power unit, and dB calculated exactly the same.
In general, dBc relative to the carrier (Carrier) in terms of power, in many cases, be used to measure the relative value of the carrier power, such as used to measure interference (co-channel interference, intermodulation interference, crosstalk, with ) and the relative magnitude of the coupling, such as stray outside interference. Where the use of dBc, in principle, you can also use dB instead.
And engage in wireless communication often encountered dBm, dBi, dBd, dB, dBc
empirical algorithms:
There is a simple formula: 0dBm = 0.001W the left to the right by 10 plus 10 =
So 0 + 10dBm = 0.001 * 10W that is 10dBm = 0.01W
it may therefore 20dBm = 0.1W 30dBm = 1W 40dBm = 10W
also left to the right by 2 plus 3 =, such as 40 + 3dBm = 10 * 2W, i.e., 43dBm = 20W, which are empirical formulas, good use.
Therefore -50dBm = 0dBm-10-10-10-10-10 = 1mW / 10/10/10/10/10 = 0.00001mW.
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dBm is calculated: (dBm and mW)
the general printing sold 802.11x wireless network AP of the top, often have specifications, there will always be inside a note to the AP (or wireless card), its transmission power (transmission pOWER) have 20dBm, or some products, is mW (milliWatts) units, such as well-known long-distance card Senao, say they have a card up to 100mW of transmit power.
Gain and Attenuation
We often hear the term gain, such as antenna gain, amplifier gain, cable attenuation and so on. Cable amplifier gain or attenuation of this we see that the meaning it represents, which is a ratio, with a power output than input power:
If n is greater than 1 dB value, which is enlarged; is less than 1 dB is the negative value, that is the loss or the attenuation of.
DBi antenna gain
Commonly referred to as transmitting antenna or the ability to receive signals with reference to a full decibel directional antenna is represented, for example the antenna has a gain 10dBi (10lg (10)) can not say that the signal power of the antenna pair 10 times magnification, but by controlling the angle of the signal transmitted, the power is concentrated to a certain direction.
In the case of equal input power, antenna gain is the actual antenna and the omnidirectional antenna at a specific power density of the same point of the spatial extent, describes concentrated radiation power of the antenna, so the antenna is closely related to the direction of FIG. Generally, the narrower main lobe antenna pattern, the smaller the side lobe, the higher the gain.
dBc: typically this is relative to the carrier power is to measure the relative values of power and carrier, for example, the same frequency / IM / cross strip / band spurious interference or the like outside the relative magnitude. 10lg (.) And 20lg (.)
Characteristics of the logarithmic decibel representation is very easy to power and power ratio. We know that the power is proportional to the square of the voltage or current, the voltage or current when converted 20lg needed, for example, (.): 1mV 1000uV = = (* 20 is LG (1000)) dBuV = 60dBuV
However, it should be noted that this is the absolute value of voltage expressed in decibels, but if the voltage ratio expressed in dB is expressed in dB and consistent power.
power:
- Watt power unit can be used Watts or dBm representation
- dB is 2 ratio of two powers :
- dB = 10 log (P1/P2)
- dBm using mW compare
- 2W = 10 log (2/0.001) = 33dBm
- = Left to the right by 10 plus 10 plus the right to the left by 2 = 3
Antenna gain:
- With linearly polarized antenna gain dBi
- Relative to the amount of the antenna gain point circle
- A circularly polarized antenna gain of dBiC
- dBiC = dBi + 3dB
- Dipole antenna with a gain dBd
- dBd= dBi - 2.15
Communication principle
1, symbol transmission rate (Symbol transmission rate) for short transmission rate, also known as the symbol rate and the like. It represents the number of symbols transmitted per second, the unit is Porter ( Baud) , referred to as B . In honor of the inventor telegraph code baud Frenchman (Baudot), it is also referred to as a symbol transmission rate is the baud rate . If the one second transmission element 2400 yards, the transmission rate is 2400B. When the symbols there are two discrete states is greater than (e.g., greater than 2 N), this time the symbol for the M-ary symbols.
2, information rate ( ): refers to the amount of information transferred per second. Units "bit / s".
3, the relationship between the two: the symbol rate: the number per unit time (1 sec) of the transmitted symbol. Information Rate: number of transmission per unit time or entropy bits.
For example: when a = 2 N,
=
; when N = 8,
4, delay: transmission delay, propagation delay, processing delay and the like.
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Periodic power signal spectrum
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