el decibel
Post on 01-Nov-2015
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1El decibel
Definicin El dB es la dcima parte de un Bel y
expresa ganancia o prdida de transmisin y niveles de potencias relativas.
dB=10 log (P2/P1)
P2: potencia medida P1: potencia de referencia
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2Escala de ruidos y efectos que producen
Grfica de 10 log (P2/P1)
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3Se observa que (1) Cada vez que la potencia se aumenta al
doble, la ganancia expresada en decibeles es de 3 dB.
Cada vez que la ganancia disminuye (prdida) en un factor de 2, la ganancia de potencia en decibeles disminuye (prdida) en aproximadamente 3 dB.
Se observa que (2) La potencia en decibeles aumenta en 10
dB cada vez que la ganancia de potencia se incrementa por un factor de 10.
Un resultado similar se obtiene cuando las ganancias de potencia son inferiores a la unidad (prdidas).
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4dBm (dBmW), dBW, dBV, dBu ???Valores de referencia
Decibels (dB) = 10 log(P2/P1) dBm P1= 1 miliwatt a 600 ohms * dBW P1= 1 watt
Decibels (dB) = 20 log(V2/V1) dBV V1= 1 volt dBu V1= 0,775 volts * (1 miliwatt , 600 ohms)
Ejercicios Cul es el valor de tensin de una seal
de -15 dBV ? Cul es el valor de tensin de una seal
de 5 dBV ? Cul es el valor de tensin de una seal
de -6 dBu ? Cul es el valor de tensin de una seal
de 4 dBm ?
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5
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6Nivel operativo estandar (SOL)
1,55-1,95 V6-8 dBu (o dBm)
Broadcasting(emisiones de
radio)
1,23 V4 dBu (o dBm)
Profesional (estudio de grabacin)
0,32 V-10 dBVSemi-profesional/Audio
Hogareo
VoltdBContexto de operacin
Absolute measurements
Electric power dBm or dBmW
dB(1 mW) power measurement relative to 1 milliwatt. dBW
dB(1 W) same as dBm, with reference level of 1 watt. Electric voltage
dBu dB(0.775 V) (usually RMS) voltage amplitude referenced to
0.775 volt. Although dBu can be used with any impedance, dBu= dBm when the load is 600 . dBu is preferable, since dBv iseasily confused with dBV. The "u" comes from "unloaded".
dBV dB(1 V) (usually RMS) voltage amplitude of a signal in a
wire, relative to 1 volt, not related to any impedance.
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7 Acoustics dB(SPL)
dB(Sound Pressure Level) relative to 20 micropascals (Pa) = 2105 Pa, the quietest sound a human can hear.[1] This isroughly the sound of a mosquito flying 3 metres away. This isoften abbreviated to just "dB", which gives some the erroneousnotion that "dB" is an absolute unit by itself.
Radio power dBm
dB(mW) power relative to 1 milliwatt. dB or dBu
dB(V/m) electric field strength relative to 1 microvolt permetre.
dBf D B(fW) power relative to 1 femtowatt.
dBW dB(W) power relative to 1 watt.
dBk dB(kW) power relative to 1 kilowatt.
Relative measurements dB(A), dB(B), and dB(C) weighting
These symbols are often used to denote the use of different frequency weightings, usedto approximate the human ear's response to sound, although the measurement is still in dB (SPL). Other variations that may be seen are dBA or dBA. According to ANSI standards, the preferred usage is to write LA = x dB, as dBA implies a reference to an"A" unit, not an A-weighting. They are still used commonly as a shorthand for A-weighted measurements, however.
dBd dB(dipole) the forward gain of an antenna compared to a half-wave dipole antenna.
dBi dB(isotropic) the forward gain of an antenna compared to an idealized isotropic
antenna. dBFS or dBfs
dB(full scale) the amplitude of a signal (usually audio) compared to the maximumwhich a device can handle before clipping occurs. In digital systems, 0 dBFS wouldequal the highest level (number) the processor is capable of representing. This is aninstantaneous (sample) value as compared to the dBm/dBu/dBv which are typicallyRMS.(Measured values are usually negative, since they should be less than themaximum.)
dBr dB(relative) simply a relative difference to something else, which is made apparent in
context. The difference of a filter's response to nominal levels, for instance. dBrn
dB above reference noise See also dBrnC. dBc
dB relative to carrier in telecommunications, this indicates the relative levels of noiseor sideband peak power, compared to the carrier power.
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8Conclusin
Vistas las anteriores relaciones de tensiones en las expresiones de db, se podr realizar mediciones para calibrar nuestros equipos con la ayuda de un voltmetro.
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