We often encounter signal level units (dBμV, dBmV, dBV, dBm, dBW), and many people are unclear about these units. When I first came across them, I was also confused for a while and had to look up some information to understand. Below, we will briefly discuss the relationships between them.
Unit dB
Let's first understand dB: dB is the national standard symbol, an abbreviation for the English word decibel or decimal Bel, meaning decibel.
dB is a pure counting unit: dB = 10logX. The meaning of dB is quite simple; it is a concise way to express a very large number (followed by a long string of zeros) or a very small number (preceded by a long string of zeros).
For example:
X = 1000000000000000 (how many zeros? 15) = 10logX = 150dB
X = 0.000000000000001 (how many zeros? 15) = 10logX = -150 dB
Decibels (dB) are dimensionless units used to quantify the ratio between two values, such as signal-to-noise ratio.
Unit dBm
dBm is referenced to a power of 1 milliwatt (mW), where 0dBm = 10log1mW.
Since it is referenced in milliwatts, it is an absolute unit used to measure absolute power.
In RF work, dBm is typically referenced to a 50-ohm impedance.
Unit dBw
dBw is referenced to a power of 1 watt (W). 0 dBw = 10 log 1 W = 10 log 1000 mW = 30 dBm.
Since it is referenced in watts, it is an absolute unit used to measure absolute power. It is used because it can express very large and very small power values within a short range; for example, 1 milliwatt = -30 dBW, 1 watt = 0 dBW, 10 watts = 10 dBW, 100 watts = 20 dBW, and 1,000,000 watts = 60 dBW.
Unit dBμV
dBV is referenced to a voltage of 1 microvolt (μV). It is widely used in specifications for televisions and antenna amplifiers. 60 dBμV = 0 dBmV.
Unit: dBmV
dBmV is referenced to a voltage of 1 millivolt (mV). It is widely used in cable television networks, where the nominal strength of a single television signal at the receiver terminal is approximately 0 dBmV. Cable television uses 75Ω coaxial cables, so 0 dBmV corresponds to -78.75 dBW (-48.75 dBm) or about 13 nW.
Unit dBV
dBV is referenced to a voltage of 1 volt (V) regardless of impedance. It is used to measure microphone sensitivity and specifies -10 dBV as the consumer line level, which reduces manufacturing costs compared to devices using a +4 dBu line level signal.