5/15/12

Random Loot: Jamming Devices

Designed for: Modern and most Near-Future or Sci-Fi settings.

Summary: Great for surprise attacks, ambushing convoys, and foiling terrorists.

Description:
In a modern setting, jammers work by broadcasting a radio signal on the same frequency as the target signal, effectively preventing data from being transmitted at that frequency. Jammers broadcast simultaneously across a large-ish frequency range, so it is rare that one can circumvent them by simply changing the channel on a walkie-talkie.

My knowledge of the physics and engineering principles involved is pretty limited, so what follows are oversimplifications at best. Also, I've assumed a modern setting, but everything here could be easily transferred to other types of games. Extrapolating to a future game would likely mean smaller jamming devices with greater range (especially for space-ship based jammers). 

Jamming Frequencies:
In game terms, a given jammer can jam a set number of device types at a given time ('cell phones' for example). For cheap models, this is set and cannot be altered. More expensive and/or larger models will have the ability to block multiple device types, and the user will be able to set the jamming frequencies on the fly. For example, a small cell-phone jammer might block all of the useable cell phone frequencies, but would not be able to broadcast outside of this range. On the other hand, a suitcase sized tactical jamming system might be able to simultaneously block 3 of any of the following: Cell phones, CB radio, wireless computer data, Radio controllers (civilian), Radio controllers (military), and GPS. If the GM doesn't want to get into a detailed frequency allocation map (and when I'm GMing, they don't), this sort of arbitrary device-based system works fine.

Jamming Types:
Overt jamming - The usual assumption in-game is that the jammer works by broadcasting some kind of white noise over the top of any existing transmissions, drowning them out. Of course, it doesn't have to be white-noise. If the PCs want to blast AC/DC or Rob Zombie over every receiver in the enemy outpost when they kick in the door, they can do that too. Overt jamming doesn't really require much skill on the part of the jammer - they just choose the frequencies (if applicable) and flip a switch. If a receiver or a transmitter wants to get through the jamming, they roll against the strength of the jamming device.

Covert jamming - I'm not entirely clear on the details, but it is possible to jam some signals in such a way that the signal 'disappears.' By doing it this way, it would be possible to jam communications without the target knowing that they were being jammed. My understanding is that this usually takes advantage of a 'feature' in the receiver - for example, if the receiver requires a particular signal to indicate the beginning of a transmission, then jamming that can cause the receiver not to pick up the transmission at all. My inclination for something like this is to make a character roll some dice - this is a good chance for the party gearhead to use all those XP they put into raising their tech skills. This would probably be some kind of contested roll between the jammer and the receiver. The particular skills will depend on what system you use. As will any modifiers for equipment quality.

Mechanics:
Jamming devices have 3 basic stats: Range (the area of effect), Strength (how hard it is for someone to transmit through the jamming), and Jamming Frequencies (see above).
Also, given enough skill and equipment, it is possible to track the source of the jamming. In this case, contested rolls are probably in order..

Example Devices:

Handheld Cell-phone Jammer
This device is actually designed to look just like a functioning cell phone, so that the user can operate it without drawing attention. 
Range: 10 meters
Strength: Modest (a skilled operator or someone with good equipment can get through it)
Jamming Frequency: 1, non-switchable, set at time of manufacture. Usually these are designed to jam cell-phones, but the concept is the same for something that jams Wi-Fi signals, or R/C controllers, or whatever.
Cost: $100 and a license (they are illegal for private citizens to own or use) or about $20 for parts if a techie wants to make one. 

Tactical Jammer
A reinforced suitcase-sized device (about 40lbs) that can be carried as a backpack or on a cart.
Range: 100 meters
Strength: Strong (getting through it is difficult, even for a skilled operator with good equipment)
Jamming Frequency: 3, switchable. GM determines options on a per model basis. 
Cost: $5000 and a license. Can be built for ~$1000 in parts.

Area Jammer
A vehicle-towed transmitter and antenna. These are very powerful jammers, generally used by the military or repressive governments.
Range: 5 miles
Strength: Very Strong (getting through it is nearly impossible without an equally strong transmitter)
Jamming Frequency: 5, switchable. GM determines options on a per model basis. 
Cost: Not for sale to civilians (unit price $30K for military acquisitions). Can be built for ~$6K in parts, but the trailer and antenna are not easily concealed.

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