Jamming devices, signals, bombs, and the President of Pakistan

[KarlGauss]

“Jamming devices” are said to have saved Pakistani President Musharraf’s life last week by delaying the detonation of a bomb until his car had passed. A bit of detail is provided here, from which I quote:

The equipment in Musharraf’s car jammed the timer for about a minute, and also jammed the remote control, the officials said.

The jammers usually work by emitting a magnetic impulse to block frequencies used to trigger explosive devices - including the electronic signals from precision timers.

Can anyone elaborate on this? Any more details on how such devices work would be appreciated. Wouldn’t this type of equipment "jam’ a lot of other stuff? More importantly, if you were/are a terrorist, why not use a timing device where the signals use a different frequency (are all frequencies jammed?)

[Q.E.D]

The description is rather vague, but it sounds like some version of an EMP (ElectroMagnetic Pulse) generator. These emit powerful electromagnetic pulses which can cause malfunctions and permanent failure in nearby electronics. One such device is available to police departments in the US and other countries. When a suspect’s vehicle passes over the device, it is triggered, emitting a strong EMP to burn out the vehicle electronics and bring it to a stop. This works because of a phenomenon called induction. Induction is caused when magnetic fields move through a conductor (or vice versa), and the conductor, in response, generates a proportional voltage across it. If the voltage is high enough, it can drive very large currents–large enough to burn out circuitry. Voltages too small to drive damaging curents can still have an effect on the operation of electronics, causing them to malfunction temporarily. My guess is that it’s something like this. Electronics can be fairly easily shielded from this phenomenon by a Faraday cage, a completely enclosed conductive box, which keeps out electromagnetic energy.

[KarlGauss]

Many thanks for your helpful answer.

I guess his limo must be a Faraday cage (in order not to jam his own stuff)?

[Squink]

Rather than a full blown EMP generator, which would cause problems for any electronics operating in the vicinity of Musharraf’s motorcade, it’s likely we’re talking about something more akin to a cell phone jammer:[[URL=http://www.intelmessages.org/Messages/National_Security/wwwboard/messages_03/6174.html]here](after a cell phone had been used to detonate a bomb which had been magnetically attached to a fuel tanker that had entered an Israeli fuel depot.
[/quote).
With homebuilt radio bombs, there are a limited number of frequencies, Transceiver/receiver pairs, and communication protocols from which to choose. Cell phones, CBs, walkie talkies, and wireless networks are all subject to jamming without resorting to EMP blasts.

At one of our early meetings Ahmed is irritable. He has just spent the day meeting colleagues to nut out a new problem: the Americans have started jamming the radio frequencies the resistance uses to detonate its bombs. He laughs when I ask if his group found a solution, but makes it clear he is not going to answer.

War On Iraq

[Squink]

Here’s my first link again:
here