Limiting RF signal reception outside of a perimeter boundary to enhance security in a wireless network. A central jamming controller (CJC) communicates with one or more access points within a wireless network to determine if link activity is present within a cell controlled by a specific access point. Link activity comprises transmissions from an authorized communication device (ACD) to the access point and transmissions from the access point to the ACD. When link activity is detected, the CJC directs a jamming antenna system to produce a jamming signal and to transmit the jamming signal outside of the perimeter boundary defined by the WLAN. The jamming signal comprises noise transmitted within the bandwidth of the channel being used by the access point and the ACD to communicate within the cell. An unauthorized communication device (UCD) outside of the perimeter boundary will be prevented from receiving the communication between the access point and the ACD because of the jamming signal.

A process and a device are useful for calibrating measurement sections for measuring noise field strengths of electrical appliances and/or to determine calibration factors for measurements of noise field strengths by means of the frequency spectrum, in particular up to 1 GHz. To this end, fields are generated by the comb generator in a known reference measurement section, preferably a standard measurement section or a free-field test site, and in a measurement section to be measured with a single calibration device or with a single interference emitter having, in particular, the same operating parameters. These fields are measured in the same manner and the calibration factors are calculated in function of the frequency by comparing the measured values.

The object of the call masking system for mobile telephones is to prevent the operation of mobile telephones which are present in a closed environment without interfering with the normal operation of other telephones which are outside the closed environment. To this effect, the system generates interference signals which will prevent the mobile telephones from receiving the signaling channels sent by the base stations (for example, GSM call signaling channel). The system monitors the power with which the carriers of the neighboring base stations are received inside the room and will adjust the interference power radiating in the signaling channels so that the carrier to interference signal ratio will make the operation of the mobile telephones impossible. The system can be applied to closed environments wherein mobile telephones should not ring when receiving a call.

The invention relates to a transmission blocker for mobile telephones as well a method for preventing transmission activities of mobile telephones in the vicinity of safety-relevant electronic devices, comprising a device for transmitting radio signals as interference signals in the frequency range of the relevant mobile radio network in such fashion that synchronization of the mobile telephone with a radio station and/or decoding of the information in the signaling channel and/or recognition of the relevant signals from the mobile radio network can be prevented.

A vehicle control system includes a radio transponder to be carried by a user, and a radio transponder reader at the vehicle for generating control signals to enable at least one vehicle function based upon receiving a desired radio signal from the radio transponder when positioned in proximity to the reader. A jammer radio transmitter at the vehicle selectively prevents the radio transponder reader from receiving the desired radio signal from the radio transponder based upon a controller, such as an alarm controller of a vehicle security system, especially an after-market security system. The controller preferably includes a receiver for receiving remotely generated signals to operate the jammer radio transmitter. The control system may also include a remote transmitter for generating control signals to be received by the receiver. For example, the remote transmitter may be a portable transmitter carried by the user, or may be a satellite, cellular or paging transmitter remote from the vehicle. A vehicle anti-hijack switch may control the transponder jammer. The at least one vehicle function may be operation of a vehicle engine or control of the vehicle door locks.