jam signal
Jamming stands for jamming. A radio jammer is a jammer that impairs or prevents the reception of radio signals. The jamming technique is not only used in radio technology and mobile communications, but also in classic Ethernet and WLANs, where it causes communication to be interrupted. In addition, such jammers can be used to interfere with radio security measures.
- A cell phone jammer is a jammer against cell phones and smartphones. Such a jammer creates interference that affects transmission and reception on cell phones in such a way that the user cannot use the mobile device in the immediate vicinity of the jammer. Such devices are used by police and emergency services to prevent communication by strangers in critical situations and during an operation. They are also used to prevent calls in churches, theaters or operating rooms.
- Radio jammers can be used to interfere with remote keyless entry( RKE) radio controls so that they can no longer be used to lock a motor vehicle. The vehicle would remain open and thieves could steal items from the car.
- With Ethernet, the jam signal is part of the CSMA/ CD access method. If a station accesses the transmission medium and detects a collision, the transmission is immediately aborted and a jam signal is placed on the transmission channel. After the jam signal is sent out, a certain time is waited before a new transmission attempt is made. The immediate abort in case of a collision and the sending of the jam signal shortens the time span to the time of collision detection. This is particularly advantageous for long messages. With Ethernet, the first station to detect a collision sends a 4 to 6 byte long bit pattern consisting of 16 1-0 bit combinations (jam signal). The length of this jam signal is thus well below the shortest allowed Ethernet packet length of 64 bytes.
- With the GPS system, there is also the concept of jamming. A GPS jammer is a GPS jammer that prevents GPS reception within a certain regional radius. Jammers with a transmitting power of a few watts can interfere with or prevent reception within a radius of a hundred kilometers or more. There are hybrid devices that interfere with the frequencies of the various mobile networks, such as the GSM network and the UMTS network and WiFi, as well as with the GPS frequencies.
