Wireless signal jammer

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Wireless signal jammers are devices used to interrupt radio signals. The low cost of manufacture of wireless signal jammers and their damaging effects have added to their popularity and frequent use.

Use for denial of service[edit]

Wireless signal jammers are most often used to interfere with wireless local area networks (WLAN), a type of denial of service (DoS) attack. Advanced and more expensive versions are used to jam satellite communications.[1]

Wireless signal jamming is a form of radio jamming. Conventionally, radio jamming was based on brute force; transmit on the same frequencies expected by the opponents' receiving equipment and with enough power to override any signal at the receiver. The original signal is lost under noise; in frequency modulation a sufficiently-strong signal can actually capture the receiver, replacing the legitimate signal entirely as a form of broadcast signal intrusion.

In warfare, intentional communications jamming is usually aimed at electrical signals to disrupt control of a battle with a transmitter, tuned to the same frequency. The most common types of this form of signal jamming are random noise, random pulse, stepped tones, warbler, random keyed modulated CW, tone, rotary, pulse, spark, recorded sounds, gulls, and sweep-through. These can be divided into two groups – obvious and subtle.

Obvious jamming is easy to detect because it can be heard on the receiving equipment. It usually is some type of noise such as:[2]

  • Random noise. This is synthetic radio noise. It is random in amplitude and frequency. It is similar to normal background noise and can be used to degrade all types of signals. Operators often mistake it for receiver or atmospheric noise and fail to take appropriate ECCM actions.
  • Stepped tones. These are tones transmitted in increasing and decreasing pitch. They resemble the sound of bagpipes. Stepped tones are normally used against single-channel AM or FM voice circuits.
  • Spark. The spark signal is easily produced and is one of the most effective for jamming. Bursts are of short duration and high intensity. They are repeated at a rapid rate. This signal is effective in disrupting all types of radio communications.
  • Gulls. The gull signal is generated by a quick rise and slow fall of a variable radio frequency and is similar to the cry of a sea gull. It produces a nuisance effect and is very effective against voice radio communications.
  • Random pulse. In this type of interference, pulses of varying amplitude, duration, and rate are generated and transmitted. They are used to disrupt teletypewriter, radar, and all types of data transmission systems.
  • Wobbler. The wobbler signal is a single frequency which is modulated by a low and slowly varying tone. The result is a howling sound that causes a nuisance effect on voice radio communications.
  • Recorded sounds. Any audible sound, especially of a variable nature, can be used to distract radio operators and disrupt communications. Music, screams, applause, whistles, machinery noise, and laughter are examples.
  • Preamble jamming. This type of jamming occurs when a tone resembling the synchronization preamble of the speech security equipment is broadcast over the operating frequency of secure radio sets. Preamble jamming results in all radios being locked in the receive mode. It is especially effective when employed against radio nets using speech security devices.

Various combinations of these methods may be used often accompanied by regular morse identification signal to enable individual transmitters to be identified in order to assess their effectiveness.

The purpose of this type of jamming is to block out reception of transmitted signals and to cause a nuisance to the receiving operator.

Subtle jamming is not obvious, which no sound is heard on the receiving equipment. The unit does not receive incoming signals yet everything seems superficially normal to the operator. These are often technical attacks on modern equipment, such as "squelch capture".

Digital networks (such as Wi-fi) may be disrupted by sending bogus control information, such as forged de-authentication packets which would dissociate the victim's devices from the targeted wireless access point.[3] Another variant is the deployment of a bogus base station to capture mobile telephone handsets; 2G networks are particularly vulnerable as, while the network authenticates the handsets, the handset has limited ability to determine if the network is legit.

In many cases, the use of jamming equipment is unlawful under national laws.[4]

Use to enhance security[edit]

Wireless signal jammers are also used to enhance the security of wireless LANs by jamming the wireless signals in a restricted geographical area.[citation needed]

See also[edit]