Voltage to dBuV conversion

What is a decibel (dB)?

The initials "dB", or "decibels", indicates that the measurement is a ratio measured on a logarithmic scale. Every time you add 6 dB, the signal level doubles. Since a decibel only indicates a ratio, you have to specify what the value is measured relative to.

In the case of radio and television field strengths, we effectively measure the voltage across one metre of space. 1uV is one microvolt, which is one millionth of a volt so 1 uV/m indicates a voltage of one millionth of a volt when measured across one metre of space.

"6 dB relative to 1 uV/m", often written as 6 dBuV/m, would be 2 uV/m and 12 dB would be 4 uV/m, remembering that every time you add 6 dB, the voltage doubles. The reason we use the dB ratio is to make the figures easier to handle when you have larger signals. 1000 uV/m is 60 dB uV/m, and 1,000,000 uV/m is 120 dB. It is also very useful when estimating aerial sizes, as the calculations involving aerial gain and feeder losses illustrate.

We always measure field strengths at 10 metres above ground level (a.g.l.), as that is where most outdoor aerials are located, at roof height.