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.
The minimum and maximum levels are determined by the linearity and noise floor of the amplifier. Anything under -63 dBm in this case isn't reliably detectable because the amplifier generates noise on its output that looks like -63 dBm on its input. Anything over -2 dBm gets clipped or distorted, so it can't be measured reliably. Say, if you put a -80 dBm signal in, the output will look like you put in a -63 dBm signal. Or if you put in a +2 dBm signal, the output might say you are putting in a -1 dBm signal. 

The frequency range is the range of RF frequencies that it can detect. Generally there are filters and what not to limit the range of detectable frequencies. It also depends on the design of the power detector itself. Anything under 50 MHz or over 3 GHz will either not be detected at all, or they will be detected at a lower sensitivity than signals within the range. For example, if you put a 4 GHz signal in at -10 dBm, the chip might read it at -20 dBm.