A radio frequency identification (RFID) reader, comprising: a transmitter for transmitting a carrier signal to an RFID device; a receiver for receiving electromagnetic signals present in an environment in which the reader is operating, wherein the receiver is operative to receive a reflected carrier signal imposing information on the carrier signal; a processor operative to collect signal data providing information relating to the signals received by the receiver, the processor being operative to identify signal data representing a return signal from an RFID device and process the data to identify the RFID device, the processor being further operative to collect signal data representing the return signal and other signal data providing information relating to additional signals and electromagnetic phenomena present in the environment experienced by the reader, the processor being further operative to make the collected signal data available for analysis in order to show characteristics of signals present in the environment experienced by the reader; a downconversion unit to downconvert the signals so as to generate a lower frequency signal representing modulated information imposed on the carrier signal in order to generate the reflected carrier signal; an analog to digital converter for receiving signal information from the downconversion unit and converting the signal data to a downconverted digital signal for use by the processor; characterised in that the processor is operative to direct the transmitter to transmit the carrier signal so that the carrier signal sweeps through frequencies in a frequency range specified so as to produce reflected carrier signals providing desired information relating to passive interference experienced by the reader. a transmitter for transmitting a carrier signal to an RFID device; a receiver for receiving electromagnetic signals present in an environment in which the reader is operating, wherein the receiver is operative to receive a reflected carrier signal imposing information on the carrier signal; a processor operative to collect signal data providing information relating to the signals received by the receiver, the processor being operative to identify signal data representing a return signal from an RFID device and process the data to identify the RFID device, the processor being further operative to collect signal data representing the return signal and other signal data providing information relating to additional signals and electromagnetic phenomena present in the environment experienced by the reader, the processor being further operative to make the collected signal data available for analysis in order to show characteristics of signals present in the environment experienced by the reader; a downconversion unit to downconvert the signals so as to generate a lower frequency signal representing modulated information imposed on the carrier signal in order to generate the reflected carrier signal; an analog to digital converter for receiving signal information from the downconversion unit and converting the signal data to a downconverted digital signal for use by the processor; characterised in that the processor is operative to direct the transmitter to transmit the carrier signal so that the carrier signal sweeps through frequencies in a frequency range specified so as to produce reflected carrier signals providing desired information relating to passive interference experienced by the reader.