Radio jamming has become a real threat to the security industry worldwide and is becoming a common crime trend. End-users and technicians need to be aware of the telltale signs of jamming and counteract them accordingly. Once detected, it is relatively simple to reduce the threat or remove it altogether.

 

 

What is jamming?

Radio jamming is the transmission of radio signals that disrupt communications by decreasing the signal-to-noise ratio.

A transmitter, tuned to the same frequency as the opponents’ receiving equipment and with the same type of modulation, can, with enough power, override any signal at the receiver. Jamming is a common occurrence worldwide and not something new.

 

 

How the Security Industry is affected by the use of jammers?

Jamming can interfere with various types of wireless equipment including the alarm panel, detectors and the radio or GSM equipment reporting to the control room. It can prevent a wireless detector from transmitting a signal to the control panel or prevent an alarm panel from transmitting a detected signal to the control room.

It is used increasingly during hi-jackings to block the GPS positioning signals and GSM tracking and is commonly used by criminals to prevent vehicle remote locking systems from activating, allowing undetected and unforced entry into a vehicle.

Wireless video systems can also be at risk due to Wi-fi links being blocked during criminal activity.

 

 

Which frequencies are mostly at risk?

When jamming occurs in wireless alarm systems, it mostly affects systems using the 433MHz “open” band equipment. These frequencies are legal unlicenced short-range open frequencies and may be used by anyone. This is the most populated and overcrowded frequency worldwide and is commonly used in gate and garage door automation, panic transmitters, geyser limiting, baby monitors, remote-controlled toys and many wireless alarm systems.

Due to the 100% duty cycle allowed and no limits on channel spacing, it will allow jamming without interruption of the signal.

Jamming of GSM transmitters is more complex and there are many custom-built jammers available that will jam multiple cellular frequencies.

It should be noted that no equipment is totally immune from jamming. With the right equipment and power levels, any radio-based system can be jammed. The question is, what type of equipment is generally available (although illegal) to the general public or criminals to carry out such an act?

 

 

Industry Solutions and SAIDSA recommendations:

1. The most effective solution to jamming in GSM equipment is the use of Dual Monitoring. This has been part of SAIDSA’s installation bylaws for many years. Dual monitoring employs the use of two different transmission technologies in two separate units.
2. Where wireless alarm systems are installed, always use a combination of hard-wired and wireless devices. Jammers cannot affect the hard-wired part of the system. All control devices and repeaters should always be protected by hard-wired devices.
3. The preferred frequency for wireless alarm systems is the 868MHz band. It is a much cleaner band and to date, no incidences of jamming on this frequency have been detected. It is the CE standard also used in SA and specifically allocated to “Alarms in general”. It is recommended by the CE standard for exclusive use by alarms and not shared by other services and devices. Alarm equipment in this sub-band may use a maximum of 10mW power with <1% duty cycle and must follow a 25kHz channel spacing. The use of anti-jamming techniques is not available in the 433MHz band, but in the 868MHz band, manufacturers have access to two versions of improving data transfer, frequency-hopping spread-spectrum (FHSS) and direct-sequence spread-spectrum (DSSS). Some alarm equipment manufacturers already make use of these technologies for wireless equipment in their range of products. FHHS and DSSS have been proven to be highly immune to jamming.
4. The use of unique licenced frequencies is also less susceptible to jamming.
5. The use of 2-way communications between the control panel and peripherals will allow a successful transmission to be acknowledged.
6. Device networking forming mini repeaters such as mesh technology in industrial systems may also ensure more successful signal transmission.
7. Where the control panel allows, jamming detection should always be switched on