An apparatus for determining operating characteristics of radio-frequency (RF) transmitting devices while the devices are in normal operation transmitting over-the-air RF signals. The apparatus comprises at least one signal sensor for receiving the RF signals, each sensor responsive to the RF signals received at a plurality of antennas or received at a directional antenna, an analyzer for determining signal parameters of received RF signals and for determining operating characteristics of the transmitting devices from the signal parameters, wherein each RF signal includes an identifier of the transmitting device, the apparatus using the identifier to link operating characteristics determined from the RF signals to the transmitting device, and a graphical user interface for displaying the operating characteristics for each transmitting device.