In an electronic article surveillance system, a jamming apparatus is provided for establishing a jamming zone in which tags can be situated and not respond to message signals from a surveillance system transmitter and in which the surveillance system receiver can be situated and still respond to tag signals.
In a wireless communication device (106) a method of detecting a narrowband jamming signal (404) includes receiving a wireless communication signal (104) and downconverting the wireless communication signal (104) to an intermediate frequency (IF) signal (525). IF signal (525) is digitized to provide a digital signal (527). Digital signal (527) is despread, demodulated and monitored for the number of phase transitions (562) occurring during a time interval (556). The method further includes comparing the number of phase transitions (562) during the time interval (556) with a threshold value (560) and determining that the wireless communication signal (104) is not the narrowband jamming signal (404) if the number of phase transitions (562) during the time interval (556) exceeds the threshold value (560), or determining that the wireless communication signal (104) is the narrowband jamming signal (404) if the number of phase transitions (562) during the time interval (556) is less than the threshold value (560).
A selective blocker for targeted mobile terminals. A signal monitor determines when a targeted mobile terminal is transmitting a signal to a base station. A signal analyzer identifies characteristics of the terminal signal and a processor produces a blocking response based on one or more characteristics. The blocking response is transmitted to the targeted mobile terminal to block communications between the targeted mobile terminal and the base station using the minimum power needed to effectively block the terminal signal so as to limit interference with non-targeted mobile terminals.
