We describe an Impulse-Radio Ultra-Wide Band (IR-UWB) receiver with I/Q demodulation made of commercial off-the-shelf discrete components. It is designed to be used in a UWB testbed for measurement and algorithm validation purposes. The central frequency of the UWB signals is 4.25 GHz with a bandwidth of 500 MHz. We have achieved a data-rate of 10 Mb/s. We experimentally validate the use of the I/Q demodulation in UWB localization. This paper can also be used as a starting point for implementing a custom IR-UWB I/Q receiver.