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Cell Phone Jammers


5 Aug 2011
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Technological advancements and their implementations are either perceived as a blessing or a curse. CHIP gives you the lowdown on cell phone jammers and weighs whether they are a boon or bane.

How dependent are you on your cell phone? We guessed right if your answer is ‘very dependent’. It is a fact that cell phones have become a necessity today—we’d gather a crowd of cynics if we said that cell phones will stop working in the future. But on second thoughts, there might be some truth to it. Let’s marinate on that and go back to the inception of mobile technology.

The cell phone fad hit the Indian market like lightning on a vulnerable night. The best part—for most of us—is that, it stayed, it grew and it has now engulfed us like a bush fire. Today cell phones are arguably a style statement but undoubtedly a necessity for convenient communication. But there are times when it becomes important not to be able to use a cell phone. Before delving into this situation, let’s go through a primer on cell phone technology.

‘E.T. phone home’
Did you know that the cell phones use the same principles as a radio? Well partially they do. We’re not talking about the internal FM radio in your phone that you use to hear music. Cell phones work roughly like walkie-talkies that you must have used in your adolescent years—the major difference being their need to communicate with a ‘base station’ instead of directly with each other. Also, walkie-talkies are half-duplex devices that transmit and receive at one particular frequency, while cell phones are full-duplex devices that use two separate frequencies simultaneously. Cell phones, better known as mobile phones, are 2-way radios that interchange radio signals with the base stations of the network provider (for example, Hutch or Airtel in Mumbai). The radios we use for listening to music also operate using radio waves, but those frequencies are very low, for example 98.3 MHz. In some phones, if you open the back panel (battery compartment) you’ll notice the frequencies (eg, 900 MHz) at which the phone can be operated. These frequencies are clearly much higher than our radio sets. Lower frequencies are used in several other applications such as aircraft communications and higher frequencies in microwave ovens. So this explains why we are refrained from using cell phones and electronic devices on a flight.

No brain-chewing
Picture yourself in a restaurant or in a library or any of those quiet places. There is this person next to you who is engrossed in a high-decibel conversation right in your face. This can be painfully brain-chewing. So what do you do? In a dire situation like this, using a device known as a cell phone jammer could bring you immediate salvation. Besides the fact that it’s illegal, using one can get you in trouble especially if you’re trying to play a prank. Although illegal in many countries like the United States, there are people who use hand-held cell phone jammers in other parts of the world. So before buying or using one, it is strongly recommended to check on it on the legal front. More on how this device works later on.

‘Let’s JAM it’
Shockingly, cell phones are being used to do a lot more than just make or receive calls and text messages (SMS etc). If you have seen the movie ‘The Jackal’, you’ll know exactly what we’re talking about. Here, Bruce Willis (the jackal) uses a cell phone to control his radio controlled sniper gun hidden in a vehicle yards away.
On a serious note: Assuming that you’ve been watching the news lately, the Mumbai train blasts are alleged to have involved cell phone triggers to set off the explosives. Check out the ‘In The News’ box to know more. But guess what—if a cell phone was the cause, then a jammer could have saved the day.
Jammers are powerful and intricate devices, but unfortunately not too many people might know much about them. So let’s dive deeper and resurrect this potential savior.

Jammers! Say what?
Jammers are radio frequency transmitters that block radio communication between devices—in this case a cell phone. They simply disable the cell phone from making or receiving voice or data calls and messaging by preventing cellular signals from reaching it. There are different types and sizes of jammers depending on their power and coverage range. Most hand held jammers look like normal cell phones and they use cell phone batteries. Larger jammers can be as big as a briefcase and can be used with a normal power outlet.
Jammers were mainly intended for military operations to track terrorist activities by disrupting their radio communication. Although they were introduced for law enforcement, they are increasingly being incorporated in other civilian areas of use.

How does it work?
A cell phone uses two separate frequencies; one is used for transmitting (talking) and the other for receiving (hearing). The signal originating from one phone is sent to the base station and from where it is relayed to the recipient. When a cell phone comes into the range of an active jammer, the signals originating from the cell phone collide with the signals of the jammer. This effectively cancels out the phone signals. Most jammers cancel one frequency of the cell phone which does the trick. Since one signal gets cancelled, the phone interprets that there is no network and hence stops functioning. In the case of rather sophisticated jammers, all the signals that the phone can receive get cancelled. This ensures that the phone does not receive an open signal to work with.

Jammers & Jargon
Since the last century, people have been using FM radios to listen to music and news. We all know that they work on radio waves that travel through air at different frequencies. Similarly, cell phones use radio waves to transmit and receive signals at very high frequencies as discussed earlier—but in this case they carry digital information instead of the analog format used in radios. Other government services like local fire departments, police department, conservation parks and emergency rescue departments also use radio transceivers to communicate. These radio frequencies can be scanned and heard on other radios if they are tuned to the same frequency. Scanning is prohibited by law in many countries, so one must know and adhere to the respective laws applicable to them.

As opposed to scanners, jammers can transmit radio signals at different frequencies. Small hand held jammers are comparatively weaker and have a range of about 30 feet, whereas larger ones might spread across foot ball fields. Jammers comprise of three main components—the Antenna, the main circuit and the power source. Cell phone jammers transmit signals at almost all frequencies and they can transmit at similar frequencies as those used by cell phones. For instance, 900 MHz, 1800 MHz and 1900 MHz (in United States) are frequencies used by GSM networks. They work well with all the other types of networks as well, such as AMPS, CDMA, TDMA, GSM and many more.

The Paint
In the near future, if you’d like to stop the usage of cellular phones at your office or your home, you’d need to simply paint it. A company called NaturalNano Inc, is in the process and development of a special type of paint that uses halloysite nanotubes coated with copper. This special paint, when applied to the exterior of a room or an enclosure might be able to block radio waves at particular frequencies, and this inlcudes cell phone signals. Other variants of this technology would also enable it to hamper the reception of WiFi communications and other electronic devices dependant on radio communication.

Halloysite Nanotubes
These nanotubes are formed naturally over millions of years by surface weathering of aluminosilicate minerals, halloysite nanotubes comprise silicon, hydrogen and oxygen. They are microscopically tiny, measuring less than 100 nanometres. Simply put, a bunch of halloysite nanotubes would show as a dot on a human hair—if you could see one. The scientists at NaturalNano are developing methods to incorporate them in electronic components for domestic and commercial applications.

Source : Chip magazine.
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