The principle of 'Jamming' is to disrupt radio signals being transmitted to a receiver that has been wired into a bomb 

The effectiveness of Jamming varies with the following factors;

The terrain, buildings, the weather, atmospheric pressure, frequency of the target, and, if the Jammer is carried or Vehicle mounted, and last but by no means least the power level of the command transmitter. 

A broadband ‘Jammer’ only has a limited amount of power it can spread over the band of operation. This limits the range of the Jammer. 

To produce high levels of radio frequency power is not only expensive but dangerous for health and could also detonate a device when least expected. 

So a compromise has to be reached.  

This is the broadband barrage type Jammer that covers all frequencies in the selected band simultaneously using a highly disruptive noise type signal. 

What must be remembered in all of this is that it is the Terrorist that controls the following;

The location of the device to be detonated, frequency, power level, type of trigger (instant /delayed).  These are things we do not know. 

If we did, things would be a lot easier. 

We have to rely on ‘intelligence’ on devices previously found and try to form a pattern for what type of device is likely to be used in the country in which we are working. 

There have been many attempts at producing the best signal for this over the years. At the height of the Northern Ireland conflict Jammers were developed that listened and recorded signals and then played them back via a radio transmitter in an effort to pre-detonate any device that was using this code. 

This was very ineffective as the Jammer also recorded other background transmissions as well, so the operators always used full active mode, which meant the system would be used without the recording side switched on. This worked as well as it could, which in reality, is all you could expect. 

A reactive Jamming system does work for RCIEDs but is very intricate to set up and only effective over selected bands. If this is used it is very effective, however the main problem with this type of Jammer is you need to know what frequency band the terrorist is using to detonate the bomb and in reality this is sometimes not possible unless there has been a regular track record of the particular bands used.

It must be pointed out the Jammer is only one tool in a whole box of tools that the Explosive Ordnance Disposal (EOD) operators have at their disposal and it will not stop all devices from detonating.

 The Jammer, for instance, will not stop a timer or a wire controlled device, it will only have an effect on Radio Controlled Devices

Radio transmitters vary from, model toy transmitters, mobile phones, pagers, to remote garage door openers, and so on.  These devices transmit on different frequencies within the radio spectrum. Our skill is to jam these wavebands very fast over set part of the wave band...such as 10 MHz to 500MHz. and 500 to 1000 MHz then we can select just the mobile phone bands 900 1800 1900 MHz etc.

Government Security Agencies through their Intelligence network usually will have knowledge of what to expect and they would then task equipment to counter these radio signals where the risk is anticipated.

Usually a Jammer will have an effective range up to120metres from the vehicle carrying it, depending on terrain.  Military experience will tell you a vehicle would have a reasonable survival chance from an explosion initiated from that distance.

Sometimes this means that the vehicle carrying the jammer gets through the kill zone untouched and the unfortunate follow up teams end up being targeted if they have no jammer protection themselves. Escort vehicles should also carry a Jammer.