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Recently, a number of prisons have come together to ask the FCC to permit jamming inside their walls and are awaiting a ruling. There are a number of issues with this way of "fixing" the problem, the greatest of which is that the guards won't be able to use their cell phones

Cell Phone Jammers

Thursday, July 23, 2009

Operating devices that jam cell phone signals is currently illegal in the United States, but that does not stop people from selling them. It is easy to buy devices on the Internet that will jam wireless signals for cell phones, GPS signals, Wi-Fi systems, and more. Jammers work by flooding an area with noise that covers the radio bands to be jammed. Since they are cheap devices that are not approved by the Federal Communications Commission (FCC), they often spew noise out into other bands as well. One U.S. cellular band is adjacent to the 800-MHz band where Nextel, some public safety, government, and business radio systems are deployed, so chances are good that these signals will be jammed along with the target bands.

Many people do not know that jamming is illegal and jammers are being used inside schools, restaurants, and other places where owners want to stop people from placing and receiving phone calls while they are inside. Lately, prisons have begun to look at deploying jammers to keep their inmates from being able to use cell phones from jail. It is illegal to have a cell phone inside a prison, but again, that does not seem to stop inmates from possessing them.

Recently, a number of prisons have come together to ask the FCC to permit jamming inside their walls and are awaiting a ruling. There are a number of issues with this way of "fixing" the problem, the greatest of which is that the guards won't be able to use their cell phones, and if the prison's radio frequency is near one of the cell phone bands, there is a good chance they won't even be able to use their walkie-talkies. If ambulance, police, or fire personnel are called into a prison and their radio system is in the 800-MHz band, there is a strong possibility that once inside the prison gates they will lose their own communications.

The real solution is NOT to authorize jammers. Since most people do not understand the consequences of installing a jammer, that could start a stampede from others who believe that if prisons can use jammers they should be able to use them.

As cell phone system subscriber, I expect to have the right to use my phone almost anywhere. Where it is not welcome in places such as doctors' offices, theaters, and certain restaurants, a sign is usually posted to inform those who enter that cell phones are not to be used inside. Mel Samples, who heads up a wireless consulting firm in Los Angeles and with whom we have worked closely over the years, has a better approach to the problem of cell phone usage in prisons. In a recent posting to the Private Wireless Forum, a Yahoo Special Interest Group, Mel put it this way:

I just can't take it anymore.

I must be missing something.

- In order to provide coverage within a prison, any given cell carrier must
have a (or 2 or 3) nearby cell site.

- The tx power is known and fully controllable for both the site and the
registered subscriber equipment on a real-time basis.

- The carrier probably already knows what site, sector, and power level is
required to process a call from within the prison.

- Add to above: mandated location technology for cellular systems force the
carrier to know, with a fair degree of confidence, which phones are, more or
less, INSIDE the fence line of the prison.

- Prisons probably do not rely on cellular services for their routine
operation so cell service is primarily for the convenience of the "guests"?
(Though the prison could apply for GETS or some other non-public, priority
class of service if needed.)

It would seem like the carriers have it in their direct control to set
system parameters that go something like:

- Do not process (or automatically force-drop) any call that originates
on cell site XXX, sector Y, above power level z, and not class of service 1
or 2.

- This could be further augmented with GPS fence lines already in the

So is anyone talking to CTIA or the carriers themselves?

It would seem like a carrier initiated and managed service area solution
would be more palatable than trying to roll back a rule that has every
marking of delivering unintended consequences.

As Mel has pointed out, there is at least one way technology can be used to prevent the use of cell phones from inside a prison. Of course, the real issue is how cell phones get into the prison to begin with. It seems to me that those responsible for the prison systems are admitting that they cannot do their job and are looking for ways to disable cell phones that have slipped by them, but jamming signals and shutting down portions of the radio spectrum is not the way to cure the problem.

Unfortunately, there are many instances where jammers are deployed, including inside schools, churches, and restaurants. Obviously, the devices are bought on the Internet from companies outside of the United States. They are shipped into the United States and deployed by people who don't understand the radio spectrum, don't know there are laws against their use, or have chosen to ignore the laws.

I hope the wireless industry and the leading wireless associations including the CTIA, APCO, NPSTC, and others will fight the prisons' request to be able to deploy jammers. If not, we could see a proliferation of them and the results could be the loss of life or property due to blocked wireless communications.

The spectrum that is being jammed is licensed to the network operators, and their job is to provide as much wireless coverage as possible. Jamming to keep criminals or impolite wireless users from using their phones is not a satisfactory way to fix either problem. In the first instance, it is the prison's responsibility to make sure there is no contraband in the prison, and in the second case, it should be up to those of us who are polite in the way we use our phones to help educate those who are not.

The push by the prisons was started by the South Carolina Department of Corrections and a copy of the petition to the FCC can be found at It should be noted here that South Carolina has a statewide communications system in the 800-MHz range and it would be rendered useless in and around all of its prisons if this passes.

If you object to jammers becoming legal in the United States as much as I do, keep your eye on this petition and be prepared to file comments against it in the near future.

Andrew M. Seybold

COMMENTS: This is an archived post. Commenting is no longer available.

Rico Camus - 07/23/2009 17:46:37

As you point out there are less invasive technological solutions to address the problems in prisons. And what really has to happen is that the prison systems finds a better way of keeping cellphones away from the inmates.

On the issue of jamming there are two ways to address this: education and enforcement. 1. Educate the public of the evils of using jammers (along with proper cellphone etiquette!) 2. The FCC has the mandate and the jurisdiction to enforce laws against illegal jammers. I remember back in the days of when I was an amateur radio operator, there were incidences of the FCC clamping down on illegal operators (unlicensed, out of band, etc). It wasn't that difficult to track them down 20 years ago and the technology must have gotten better. Just shut down the illegal jammers where ever they may be.

Andrew Seybold - 07/23/2009 17:50:12

Rico--thanks for your comments and you are correct--but what you are missing is that 20 years ago there were five or six (at least) field enforcement people in each FCC office--today that number is either zero or 1--another issue that needs to be delt with as more of us go wireless

James Norman - 07/23/2009 19:15:27

Andy, if the cell strength inside the prison fence were 'not good,' to 'useless;' then the pressure to have the contraband inside the fence would lessen. The cash-strapped prison system would benefit and cell service (and other services in the future) would be maintained elsewhere. This would be a 'service' that the cell providers would be required to provide in order to keep their license. Now let's see who screams? jim

Nick Ruark - 07/23/2009 20:44:19

Andy - One little fact that seems to be overlooked with respect to signal jammers is that while technology in the area of wireless communications has advanced by leaps and bounds in recent years, no one has yet been able to successfully circumvent the laws of physics that apply to the use of these devices. Therefore, the reasons for the technical laws, rules, and regulations currently in place that prohibit the use of signal jammers must still be valid. Thus, IMHO at least, it would seem appropriate that some type of effective educational effort coupled with rules enforcement against those who import, sell, and use such devices should be aggressively implemented and pursued. Otherwise, sit back and prepare for the potential "spectrum chaos" that most certainly will result should the corrections and prison industry (and others sure to follow) gain approval to deploy this type of disruptive technology.

William Brownlow - 07/24/2009 06:08:40

The discussion over jamming equipment has raged for at least a year with the latest incarnation being derived from CellAntenna that has developed some very sophisticated equipment and successfully deployed the systems in other countries.

At IWCE, Mr. Melamed the President and CEO was making the rounds of many booths to speak with people that had lined up against earlier requests for waivers to allow demonstration of his system in various venues around the country. The technical presentation shown me using PowerPoint was impressive and the claim was made it could be tuned to operate only on the cellular interleaved frequencies leaving the public safety frequencies unhindered - well at least that is the claim.

I remain opposed to the deployment of commercial jamming equipment simply for the reason the technology, like using cell phones inappropriately, can be abused. Deployment of a jammer requires it to operate on licensed spectrum, and the operator of the jamming equipment is not licensed for the very frequencies they are jamming.

Widespread commercial deployment of jamming equipment would require constant maintenance to insure it remained on its unlicensed frequencies and did not cause "harmful interference" to adjacent or co-channel operations.

The deployment of a jammer in correctional institutions is very similar to the deployment of a DAS in that it uses an array of antennae distributed throughout the facility with all the inherent cabling necessary to feed the unlicensed signal to the emitting antennae.

This same distribution system could be used in reverse, not to block, but to triangulate and locate a transmitting device which is entirely permissible under regulation, but the prisons don't want to do that as it puts their officer at risk when they have to enter the cell blocks on a search mission. Perhaps the state PUC which has regulatory power can set operating rules making the reception of a cellular signal greater than a -95 in or on the open grounds of a correctional facility subject to sanction.

Just some thoughts.

Wayne Longman - 07/24/2009 07:04:21

Gelocate the phone and deny service within prison boundaries. May need a multi-band fempto-cell on the grounds for more accuracy.

Joe Blaschka Jr. PE - 07/24/2009 07:43:54

Think also of the increased maintenance and engineering costs to the cell carriers. Customers will complain (not prison "customers" but other customers) that their cell phones used to work in this resturant, office, location, etc. and now don't. The cell carrier will need to send a technician or engineer out to the area to see what is going on only to find a jammer. Cell technicians have already reported this problem with the illegal jammers, legalizing them will make the problem worse. Look at the problems with the illegal BDA's that get installed all over the place. There are many other options ranging from tacking the calls to denying the calls. I hope the cell carriers are listening, assuming they aren't being jammed, and come up with an alternative before Congress does.

Christopher Guttman-McCabe - 07/24/2009 12:43:22

As the head of regulatory affairs at CTIA, I wanted to weigh in responding to both Andy's article, as well as the postings. I wanted to share some of our efforts to date. First, the wireless industry has reached out to the corrections community to educate them on alternative (and non-interfering) solutions. We also convened an all-day meeting here at CTIA of alternative technology vendors. In that meeting we identified two types of viable technology solutions, one involving cell detection (the ability to identify and confiscate, through sensors and triangulation, a wireless phone when it is turned on in a prison), and a second solution we call "managed access," which basically does exactly what one of the postings proposes -- it identifies a call from inside the prison and "manages" whether that call will have access to the carriers' networks. We have made representatives in Congress, at the FCC, and in the corrections community aware of these solutions. We have set up a demonstration with the Maryland Department of Corrections for this managed access technology. We also have educated countless policy-makers, reporters, and corrections facility leaders of the signifcant dangers of using jammers, pointing to instances of interference when jammers have been used in the United States (illegally) and in Pakistan, India, Brazil, Mexico, and other countries. Hopefully we have made some headway.