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: 
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.
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.