USS Clueless CDMA FAQ -- Is it possible to jam CDMA?

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Is it possible to jam CDMA?

Short answer: It's possible, but it's impractical.

Long answer: People who ask this question tend to divide into two groups. The first group are those who are concerned about people who are stupid enough to use their cell phones in environments where the radio frequency emissions (RF) could cause problems, like near operating jets, or in hospitals where people are wired to pacemakers. The second group are those who are fed up with listening to phones ringing in theaters and restaurants.

RF jamming divides into active and passive. Passive jamming means shielding; the ultimate form of this is known as a "Faraday cage" and it means you are surrounded by conductive metal or fine screen on all sides, including top and bottom. Active jamming means to broadcast meaningless RF at the frequencies in question at sufficient power level to disrupt the behavior of the device -- in this case, the CDMA cell phone.

Active jamming is a lost cause. Not only would it be a violation of FCC regulations (or those of comparable authorities in other countries) but CDMA uses spread spectrum. Spread spectrum was developed during World War 2 precisely because it is exceedingly difficult to jam with active jamming. And in many cases (the hospital heart ward) the cure would be worse than the disease because the transmit power levels required would cause more harm than the phones could.

Passive jamming would require that metallic shielding be built into the walls of the structure as it was being constructed. While this might work for a theater, it's impossible for any structure which has windows unless you put grounded screens over every single one of them. (Which might actually be possible for the heart ward, but is probably impractical for a restaurant or an airport.) And it certainly wouldn't be cheap in any case.

Captured by MemoWeb from on 9/16/2004