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Cellphones: To jam, or not to jam?

Read time 3min 10sec

On Monday, the Independent Communications Authority of SA (ICASA) will open a can of worms as it starts public discussions in Johannesburg on the legality of cellphone signal blocking devices.

With cellphones now very much a feature of everyday life in SA, they have also become an everyday annoyance for many. No space is sacred and people have been imprisoned for contempt of court, performers have interrupted shows to berate audience members and at least one preacher has denounced the devices as demonic.

The technology to block cellphone reception in any given area is available and relatively cheap, essentially broadcasting noise on the same frequency used by cellphones. By blanketing the right frequency, all incoming and outgoing signals are neutralised and phones in the affected area act as if they were outside a base station coverage area.

Although technically illegal in SA, the devices have been used. According to press reports, the car carrying Libyan leader Muammar Gadhafi during the recent racism conference in Durban carried a cellphone-blocking device and it is thought that the protection units of figures such as president Thabo Mbeki also employ them.

In such cases the motivation is to increase security rather than avoid annoyance. Cellphones are cheap, effective and easily obtainable detonators that can be used with most kinds of bomb and there are reported cases of such use in SA by more than one organisation.

That is why the SA Police Service will argue for permission to use blockers in bomb-disposal and possibly other situations.

Their use outside of the control of law enforcement is likely to be far more controversial. Banks ban the use of cellphones on their premises as they can be used to co-ordinate a robbery, but some security systems use the same frequencies, making jamming impractical.

Blocking in venues such as cinemas faces two sets of objectors. Emergency services personnel and other professionals on regular standby duty would argue that blocking can prevent them from leading normal lives and enjoying the amenities available to others.

Cellphone companies - all three will make submissions on Monday - are likely to argue that user education would be more effective than jamming.

The providers will also raise the technical arguments heard against blocking elsewhere in the world. Although jamming is easy, confining the blocked area is not and an overpowered or faulty unit can blanket signals over a far wider area than intended. It could also interfere with nearby base stations, causing signal degradation for users outside of the blocked area.

There are also more philosophical issues around jamming. It could be said to be punishing the polite, who know how to use their silent vibrate function, for the sins of the impolite. Also, the licences granted to cellular operators guarantee them exclusive use of certain frequency blocks and the right to use that spectrum anywhere in the country. Blocking infringes on those rights.

Perhaps the most potent argument against jamming is the freedom to use passive blocking. Many building materials will block or absorb radio signals and there are no restrictions on their use. A team of Japanese engineers recently announced the development of a fairly cheap panelling that can be added to existing buildings; a layer of nickel-zinc ferrite between thin slices of wood. Four-millimetre thick panels of that composition proved sufficient to stop most cellular signals.

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