![]() When the unit was first devised, it was mainly used to measure 600 ohm telephone line. This unit of measurement was an industry standard in the 1940’s. This means that 0 dBm = 1 milliwatt, and it has no direct correlation to voltage or impedance. The term dBm expresses an electrical power level, which has the reference at 1 milliwatt. Regarding these 2 categories, there are several types of decibels which we will enumerate and explain in the following part of this article. We’ve talked about decibels and how they relate to volts and watts, but where is the loudness I’m used to talk about when I mention decibels ? That’s because decibels relate to 2 things : electrical signals and acoustical signals. When you double the voltage, you get 4 times the power. P = Power in watts E = voltage in volts and R = resistance in ohms.Īs you can see power is proportional to voltage squared. Why is it that when we double the power, we get a 3 db increase, but when we double the voltage we get a 6 db increase ? This is because of the relationship between power and voltage. If it is 1/10 the voltage, it is 20 dB less (-20 dB). Whenever one voltage is 10 times the other, it is 20 dB greater.If the voltage is a half the other, we are talking about 6 dB less (-6 dB). 4 times would be 12 dB, 8 times would be 18 dB an so on. Whenever one voltage is double the other, it is 6 dB greater.įor voltages we can draw the following conclusions : What is the ratio in dB of 100 volts to 10 volts ?. ![]()
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