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What are units based on dB?
dBW, dBV, dBmW, dBµW, dBmV and dBµV
Let us see some commonly used decibel based representation units in wireless communications. The difference between these entities lies in the type of ratio and the reference levels of the quantities. We can have power ratio, voltage ratio, current ratio, and so on. Reference levels can be 1 W, 1 V, 1 mW (milli-watt), 1 mV (milli-volt), 1 µW (microwatt), 1 µV (microvolt), and so on.
Voltage based dB representation units
The ratio of two voltages will be mapped on to the decibel scale. Often, one of the two quantities of the ratio is a reference and the other is compared with the reference. Some of the commonly used voltage based dB representations are dBV, dBµV, and dBmV
Signal Voltage Levels of Cable Tv
The signal voltage levels of cable TV (terrestrial TV) system are often expressed in dBµV. The signal voltage level is specified with reference to 1 micro-volt.
Numerical Example
A TV signal voltage level is specified as 47 dBµV. What does this indicate?
Soln. The reference voltage level is 1 micro-volt. The signal voltage level is 47dB μV. A positive dBµV indicates that the signal voltage level is greater than the reference voltage level. Let us find how much the signal voltage level greater than the reference voltage level is.
$$47dB\mu\:V=20log_{10}(\frac{V_{OUT}}{1\mu\:V})$$
$$log_{10}(\frac{V_{OUT}}{1\mu\:V})=2.35$$
$$(\frac{V_{OUT}}{1\mu\:V})=10^{2.35}\sim\:224$$
$$V_{OUT}=224\mu\:V$$
Therefore, the output voltage is 224 times the reference voltage of 1 microvolt.
Similarly, we have power based dB representation units. The meanings of some of the most prevalent representations are shown below in the table.
| Representation | Inference |
|---|---|
| dBW | Reference power level is 1 W. A positive dBW indicates the output or received power level is greater than the reference power level. A negative dBW indicates that the output power level is less the than reference power. |
| dBm or dBmW (m for milli) | Reference power level is 1 mW. Commonly used to represent received power levels in mobile and satellite communication systems. We can have positive and negative values of dBmW |
| dBμW (μ for micro) | Reference power level is 1 μW. Both positive and negative values exist for dBμW |
| dBV | Reference voltage level is 1 V. We have positive and negative values of dBV |
| dBmV (m for milli) | Reference voltage level is 1 mV. We have positive and negative values of dBmV |
| dBμV (μ for micro) | Reference voltage level is 1 μV. Both positive and negative values exist for dBμW |
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