Question: I've been looking at various RF power detectors for a project I'm working on, but I don't quite understand what the manufacturers mean by "dB range".

For example, the [LT5534](http://cds.linear.com/docs/en/datasheet/5534fc.pdf) Log RF Power Detector has a frequency range of 50 MHz - 3 GHz; the minimum it can detect is -63dB and the maximum is 2 dB. What does that mean?

Answer: 
Here is an extract from the LT5534's data sheet. Note the part enclosed in a red box: -

![enter image description here](https://i.stack.imgur.com/eZ03w.jpg)

What that line is saying is that the input power range is -63dBm to -2dBm i.e. a range of 61dB as indicated in the line below.

If you are still confused then 0(zero)dBm is 1 milli watt and if the circuit impedance is 50 ohm this means: -

\$\sqrt{P R}\$ volts or \$\sqrt{1\times 10^{-3}\times 50}\$ volts = 223.6mV RMS.

If you are still confused -63dBm is a power level of 501.2 pico watts and -2dBm is a power of 631 micro watts. I think you should be able to convert these to voltages by now.
It is actually -63dBm and 2dB , depending on the frequency. It means the range of RF signal to which there is a linearly related output voltage. This detector is equivalent to an anti logarithmic function.