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dBm or dB mW (decibel-milliwatts) is a unit of power level expressed using a logarithmic decibel (dB) scale respective to one milliwatt (mW). It is commonly used by radio, microwave and fiber-optical communication technicians & engineers to measure the power of system transmissions on a log scale , which can express both very large and very ...
A power level of 0 dBm corresponds to one milliwatt, and 1 dBm is one decibel greater (about 1.259 mW). In professional audio specifications, a popular unit is the dBu. This is relative to the root mean square voltage which delivers 1 mW (0 dBm) into a 600-ohm resistor, or √ 1 mW × 600 Ω ≈ 0.775 V RMS.
When the test impedance is 600 Ω resistive, 0 dBm can be referred to a voltage of 775 mV, which results in a reference active power of 1 mW. Then 0 dBm0 corresponds to an overload level of approximately 3 dBm in the analog-to-digital conversion. Given a sinusoid signal of 0.775 V RMS, the power at a zero transmission level point is:
A field level (or root-power level) is a logarithmic quantity used to measure quantities of which the square is typically proportional to power (for instance, the square of voltage is proportional to power by the inverse of the conductor's resistance), etc., with commonly used units neper (Np) or decibel (dB).
The decibel watt (dBW or dB W) is a unit for the measurement of the strength of a signal expressed in decibels relative to one watt.It is used because of its capability to express both very large and very small values of power in a short range of number; e.g., 1 milliwatt = −30 dBW, 1 watt = 0 dBW, 10 watts = 10 dBW, 100 watts = 20 dBW, and 1,000,000 W = 60 dBW.
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For very low-power systems, such as mobile phones, signal strength is usually expressed in dB-microvolts per metre (dBμV/m) or in decibels above a reference level of one milliwatt . In broadcasting terminology, 1 mV/m is 1000 μV/m or 60 dBμ (often written dBu). Examples. 100 dBμ or 100 mV/m: blanketing interference may occur on some receivers
−30 dBm tech: approximate consumption of a quartz or mechanical wristwatch: 3 × 10 −6: −25 dBm astro: cosmic microwave background radiation per square meter 10 −5: 5 × 10 −5: −13 dBm biomed: sound power incident on a human eardrum at the threshold intensity for pain (500 mW/m 2). 10 −3: milli-(mW) 1.55 × 10 −3: −4.7 dBm