Detect and block LTE band

I have a conceptual question and I hope someone can help me clarify or find an answer

In the context of using a telephone inside a room or office, is it possible to detect an LTE band for example band 7 and band 28, and at the same time block communication with those bands?

I have the doubt if this can generate a RF feedback between the blocking circuit and the detector circuit, so in practice it would not be possible, due the false positives.

I am not an RF engineer and I am not proficient at that level, please someone who can explain to me if this idea is feasible.

Is this for a product or a test? It is a viloation of FCC rules to intentionally block communicstions.

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Technically you could stop the jamming signal for a brief moment and listen to see if you still detect the original signal, then resume/stop accordingly but like @steveg mentioned such a device would be illegal.

Hello, yes, correct, but in my country technically it is not illegal but still I think that this problem is still under discussion.
The context of this is for an industrial use to avoid accidents. Truck drivers have a bad habit of using telephones on their workday, accidents often happen and there is no way to verify if it was because of the telephone. So the last solution is to block the communication of these inside the cabin.

But I just wanted to know if electronically it is possible or feasible to work reliably

Hi! I do not wish to open the Pandora’s box of the context for that question - only to say, the implications of this are many, not limited to legally, ethically and even though your intentions are for OH&S if there is an accident and no coverage you could have the opposite effect.

None the less the technical side is interesting though, however working in the telecoms industry I know most of the engineers I know would be unlikely to answer the question - knowledge is not illegal itself but it’s a slippery slope.

I am curious as to what country you are in and what regulations are in place!

I do sympathize with the issue, I have family working on OH&S in mining, and know the potential issues - but I would look for other solutions

Florida Man tried this and was fined $48k usd. I wouldn’t suggest you think about this technology–

Thank you, I understand the problems involved in the use of this type of technology … But the workspace in the mining industry is not publicly accessible, but rather private. They have their own communications networks to control the haultruck fleet, etc. I don’t know if they would have problems with the FCC

Anyway, I just want to know if there is a possibility of feedback being generated in the detector and jammer circuits, which would mean that the idea would never work.

it is a purely electronic question

@axtrem It is extremely difficult to fight stupidity. If the drivers are stupid enough to use their phones while driving heavy equipment, you can do pretty much what you want and they’ll get around it.

If I were you, I would rather have a look at just making it difficult to get a radio signal inside the car? If the problem is serious enough, you might be able to turn the drivers compartment into a Faraday cage that would block the driver in that specific car from using his private phone, while other comms could have an external antenna? :wink:

Shielding windows requires special glass though, so it might not be feasable I would generally support the others here in saying that jamming others is not a good idea. Imagine a huge accident in the mine, but nobody could call an ambulance…


I completely agree.
Some colleagues also thought of the idea of the faraday cage, but there are other devices inside the cabin that require communication, such as radios. I am not an expert on the subject, but perhaps designing faraday cages and that they work correctly for specific lte band, may be very complex. Maybe external antennas can be used for radios, I don’t know.
Another big problem is that many times certain technologies must be removed due to pressure from the workers’ unions, as was the case that a system with cameras inside the cabin had to be eliminated because it invaded the “privacy” of the truck drivers.

Maybe the idea of @voltlog could be good enough or I should stop participating in this “prototype”

It is a tough problem to solve. I commend you for trying. Whatever solution you come up with has to satisfy a lot of requirements. Beware of the law of unintended consequences. I suspect the union would force you to remove cell phone jammers.

An alternative approach might be to detect the cell phone actively making a call while the truck is moving. Over the road trucks with electronic logs will stop moving if a driver is not logged in. You could stop the truck from moving, or just log or report the activity.

I shall pontificate briefly. :grin: Technical solutions for social problems rarely work well.

A union will defend freedom of association; the capacity of the worker to speak with their union while in the place of work and at all other times. The worker is obliged to do so safely. Exactly what is safe depends on the speed, vehicle, load, road, traffic and environment. In most jurisdictions with unions, an employer is responsible for describing how to work safely, and sometimes must do so with the union.

Accidents can also be intentional, with workers using phones to coordinate via side channel. Blocking the phone won’t solve that scenario, because the workers will switch to sign language, planning, or UHF CB radios and a spoken code.

Best is to ask the workers how they would like their use of phones to be made safe.

It isn’t practical to detect the difference between an idle LTE phone and an LTE phone being used for a conversation. Both generate RF packets. The codecs used can result in irregular packets (silence suppression, background recreation), so it sometimes isn’t practical to prove a voice call is in progress.

If it were me, I’d avoid working on the problem because I’d rather not be the target of revenge, even misplaced revenge. Note that this thread is visible to the general public; no authorisation was needed to see it.

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It’s illegal (in some places) to block the RF band, but it’s never illegal to block the audio band - Just build a circuit to detect signals in the applicable RF bands that are over a certain signal strength, and last for more than a few seconds. When such a signal is detected, sound an annoyingly loud white noise in the 1-3kHz range that will block/mask any conversation. :slight_smile: :rofl: :rofl: If the phone genuinely needs to be used the driver can turn off the vehicle and/or get out of the cab.

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Thanks for the answers,
it’s true, the thread is public, I don’t know how to leave it private, if I can’t I’ll delete it

The problem is not only the use of the telephone for calls, but also for messages app, whatsapp, facebook, etc.
Stopping a haultruck in mining is not allowed unless it is maintenance, because the loss in production / economy is enormous. In mining the effective working time of a haultruck is constantly monitored to increase production.
There is also another problem, outside the cabin there is CPE LTE for communications of the operation of the trucks. I don’t know in which bands they operate.

Now I think that blocking the phone communication will not solve the problem, because the problem is the bad habit of the driver, so you have to eliminate that bad habit. And maybe a solution is to have a reliable system that can detect the intensity of transmission of the uplink in the transmission of the phone(I suppose) and then register the event to apply discounts on your salary.

As others have already observed: jamming is illegal in most places. It’s not very hard to engineer. It is harder to stop reliably at a sharp boundary.

What is legal, and fairly easy to implement in a fashion legal almost everywhere is detecting a mobile. It transmits in a different range of frequencies from the base station, and regularly chats with the network to remain in communication. Proximity is still an issue, though. It’s hard to tell the driver from the foreman standing 10 meters away. Detecting an active call vs an idle mobile is actually pretty hard. Not impossible, but very hard to do with any degree of uncertainty.

You also have to contend with evolving standards. What worked well for 3G would not for LTE. 5G is being fielded, and 6G (really!) is in the labs.

The Faraday cage approach is simple conceptually, but difficult to implement practically in a manner that doesn’t require constant maintenance. I’ve worked on shielded conference rooms, and even though they are in environmentally controlled space, maintaining shielding effectiveness is a continuing challenge. Outside and in the vibration environment of a vehicle, its much harder.That and users quickly learn how to circumvent them.

It has some significant moral considerations as well. What if an emergency call is blocked? Who is liable?

I don’t believe the topic needs to be deleted, it conveys useful commentary and no one advocates violations of the law, quite the contrary.


maybe activate the jammer if the speed is not “safe” to use a cell phone… it’s like almost illegal. In my country, it is not allowed to drive using the telephone for any citizen with a driving license.

The trick here is how do you know it’s not safe? If the vehicle is moving at all?

What if the driver is carrying an injured worker and calling for help? You just can’t know, and while rare all you need to do is be wrong once to do harm. The ‘greater good’ argument is hard to make because you can’t prove what tragedy you prevented. There will be plenty to testify show what you’ve caused.

The earlier statement that this is a social/moral problem that won’t yield to a technical solution is almost certainly correct.


One last thought on this: “that which is measured becomes the goal.” The Hawthorne effect is a powerful management tool.

Maybe you could monitor mobile transmit times and report The driver’s transmit times vs the average. Not post for all, just to the individual driver and the average.

I managed a standards group for a while. Lots on international calls and long telecons. The folks in my group had some pretty impressive mobile bills - one over $5K US in a month. My management wanted me to shame the high time users. I made everyone review and sign off on their mobile and wired phone bills. It took a month (one additional billing cycle) for the group bill to be cut in half. It settled at 25% of the previous year’s average.

This can backfire if management are jerks and workers are trying to get even. I could have easily set up a contest for the highest mobile bill by accident.


sounds good, then we would only need a reliable device to detect the use of the phone (calls, chat, etc) but if the user is using spotify it would not necessarily be a detection event due to data consumption using the 3G / 4G network, because he would only be listening to music with his phone. So I think I have no solution

I’m not one to advocate surveillance, but it seems to me a dashcam solution with periodic checks or a required app that minimize s functions while on duty might be able to deture unwanted phone use. Sufficiently motivated people will always find was around things, but you can probably reduce incidents with unique strategies.

cameras invade workers’ privacy. Now, I think that the mining company will not find a solution technologically speaking to this problem, as someone mentioned at the beginning.