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Jamming Metal Detector Use


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Hello, now here’s an opener that might just get me banned on my first post!

Bear with me, my intentions are pure :)

Does anyone know if it would be possible to jam an MD signal? The reason I ask is to combat the evident problem we have in the UK with “nighthawks”, illegal detectorists.

Over here, any landowner can grant permission for detecting on their land (with caveats, known historic sites are protected by law). What often happens is that such a permission is granted and a detectorist innocently sets about his / her business. Someone less scrupulous spots this person and assumes there may be something important there, so shows up at night with a couple of friends and the landowner awakens to a field / lawn full of holes, then bans metal detecting.

Historic sites are also looted.

Just an off the wall question, how tricky would it be to build a device to block this on a piece of land? Anyone any ideas?

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Certainly possible, but difficult. All detectors operate on a frequency, and a transmitter running at the same frequency will jam it. But there are many machines running at different frequencies, and they have ability to adjust in a range.

Option one would be a shotgun transmitter putting out a broad spectrum signal to jam all the range of frequencies detectors operate at. I can't imagine this working in the city as you would be jamming more than detectors, but maybe on a ranch in the middle of nowhere.

You could also use a frequency scanner to locate a detector in use within range, and then have the jammer work only against that frequency, so much more targets. Still no idea on the legalities, but technically it should be possible. Cost effective? I have no clue.

Simple example. Turn on a Minelab GPX 5000 in the middle of a field. Nobody will be able to get within 50 feet of that machine with another detector, as the GPX is basically throwing off it's own portable jamming field. So there is an at least 100 foot diameter circle that been effectively jammed. Expanding the concept for range is the problem though, as power requirements escalate rapidly.

Kind of related. It is possible to block cell signals. It is also illegal in many places. Police jammers, same deal. Jamming is as much a legal issue as anything, and I'd cross that bridge first, before worrying about the tech aspect.

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1 hour ago, Steve Herschbach said:

Police jammers, same deal. Jamming is as much a legal issue as anything, and I'd cross that bridge first, before worrying about the tech aspect.

The Federal Communications Commission (FCC) here in the USA has strict controls over these kinds of things.  And some local laws even prohibit (or at least used to prohibit) scanning police frequencies (i.e. automatically searching multiple frequencies to pick up a police communication), so it's more than just transmitting that can be illegal.

How are metal detectors legal?  Because their RF range is limited due to their low power, for starters.  (Metal detector manufacturers must go through certification with the FCC before they are allowed to sell a new model of detector.  It's not just the low range that allows their use.)  Building a device capable of jamming (at a distance) is unlikely to fit under the low range allowance.  And that seems likely to be just the tip of the iceberg of laws that such a device would break.

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Bluetooth sweep frequency jammer might knock out their headphones if they are wireless. Not sure what kind of range they have.

Wouldn't be easier to put in some motion sensing lights and an alarm?

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?? That is some kind of easy. If it was my property I'd pepper it with scrap metal. May be there is a milling company close to you. Asking them for scrap metals made of brass, copper, iron, aluminum, etc...and what they want for, and then sow this. Will be fun to watch them...lOl 👀😜😂🤣

oops...forgot this...: Welcome aboard, WhiteRabbit.😊

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How about a good old fashioned stakeout?

Just remember to have eyes on the site!

 

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I use cellular deer cameras for security. If someone tried to steal or damage them it would be too late, the photo would already be sent to me. They are easy to hide. They are relatively inexpensive and some last a long time (up to a year) on lithium AA batteries. Non-cellular cameras are less expensive. All can be bought with a steel box that makes them tougher to get to or damage.

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Thanks a lot for the answers, some good ideas.

With regard to the law, I’m based in England so the laws will differ here. I’m a network engineer by trade, so I do know about the upper limits on signal strength and I’m also aware of which frequencies / bandwidths are public and which aren’t.

Also government licences can be granted for specific uses.

Last week a significant Roman settlement was discovered close to where I live. An article about it was published in the local newspapers and *that night* it was hit by what appears to be a team of nighthawks.

Nobody knows what they took and, since they will struggle to sell on the open market, their finds will go onto the black market. Consequently, a good chunk of British history may disappear forever.

That’s the kind of thing we are up against.

Britain currently has very permissive metal detecting laws, but if this continues, then these laws will be changed. I can foresee licensing, then a complete ban on the sale of detectors.

I have thought about scattering aluminium scrap all over the place, but you can’t do this on historic sites as it would contaminate the archaeology.

What got me thinking was hearing a friend complaining  that he thought his detector was broken before he realised he was near an electric fence that was causing interference...

Surely this could be replicated.

I did look into the designs for a home brew EMP which, believe it or not, may actually be legal to use outside cities in the UK (I’ll have to double check this!), but whatever the case, I don’t want to go wrecking peoples’ property, I just want them to know that hitting x site is going to be a waste of time.

Steve, thanks for your input. I appreciate that detectors work on different frequencies and did consider buying a few common models and amping up the signal, but that wouldn’t exactly be cheap (my CTX3030 alone is £1,700 over here). From what I have read, most detectors work in the low kHz, 1.5kHz to 40kHz and so I was wondering what decide would be required to bleed all over this frequency. It doesn’t necessarily need to block signals, just interfere with them enough to render detecting not viable. A shotgun approach might work here.

However, your idea about using a frequency scanner and locking into that is more elegant. I’m an IT engineer who does a lot of robotics / IoT work in my spare time, so I could trigger all kinds of alerts / events from this.
 

Ok, this sounds technically viable. I’ll check the laws and devices available and let you know what I discover if you’re interested?

I’d also really appreciate any further ideas.

Many thanks.

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Oh, regarding cameras.

They are just no deterrent. People cover their faces, police are often slow to respond to such crimes and archaeologists don’t usually have the funds to finance private security. 
 

Saying that, three people were recently identified from footage taken with wildcams during the day after their mugshots were plastered all over Facebook.

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