been having a good think about defeating LTI2020's
Discussion
I've thought of a very simple way to confuse an LTI2020, that doesn't involve any electronics, jamming, filters, or anything that disguises the number plate. Going to do a few tests with a Helium Neon laser on my own car (so i can see it) and I'll let you know the results, and post my little idea when done.
FYO.........
I earlier posted this on another thread if anyone is interested..........
Laser guns don't use doppler shift. The reflected light is doppler shifted of course, but the camera doesn't make use of this.
As your technically minded, he's how an LTI2020 works
There is a 905nm Infra red solid state laser module with deam divergence of approx 3mrad. It flashes 44 pulses of IR over a period of 0.3 seconds. This light is aimed at something very reflective, ideally the numberplate of a car which who's backing material has the same reflective properties of a 'corner cube' mirror, known as a reflex reflector (it reflects light in the direction in which it came to a tolerence of +/- 3 degrees) The reflected light pulses are picked up by an IR dependent resistor network behind refracting optics in the LTI 2020 and the time intervals are recorded into memory. The time intervals plotted against time create a gradient which directly correlates to the distance travelled by the point of reflection, and therefore the velocity. The LTI must recieve at least 30 similar reflected pulses to achieve a legitimate reading. It does this by applying the mathematical 'least squares' algorithm. (look on the net about 'least squares')
Way's to block an LTI2020.
Don't have a reflex reflector back plate on your numberplate. - illegal as it's a requirement of the number plate legislation.
Sandwich a sheet of IR filter gel between 2 of the layers when you have your numberplates made.
Not illegal. The legislation says that the numberplate should reflect light, and be easy to read. Say's nothing about IR.
Quick decelerating.
legal of course, and causes the LTI2020 to throw an error as the 'least squares' algorithm can't establish a grandient. (the gradient would be of a curved line as your velocity is changing quickly)
Put a lot of little spinning mirrors around the front of your car that spin in the airflow. This causes a lot of spurrious random reflections (the LTI2020 also looks as pulse width and shape to make sure it came from the same object (to try to eliminate sweep errors))
ACTUALLY............... why not put a load of reflex reflector material on your radiator fan?. just a thought.
The LTI2020 is quite a well thought out little s**t of a device. Matched only by the arrogance of their phone staff if you give them a call.
The best jammer of them all, if you can make one, is one that will measure your speed, and always return pulses that will make the LTI2020 read 30MPH, regardless of speed.
I'm sure you could do the maths. And you can buy laser modules!
just like IR remote controls, the lights is also modulated. not sure what frequency. Modulating it increases the range very significantly. For eg. a TV remote control LED only has a range of about 6 inches, but when modulated that increases to (theoretically) hundreds of meters. Installing IR's is like trying to drown out a very loud dog whistle with a bass guitar!.
Ideally, you want to try to make a pair of IR stobe lights, running at about 34kHz.
As I understand it, the CCTV units that the camera vans use filter out IR. (I've never yet seen the bright 'star' effect of the laser from a numberplate on any recording) so it's unlikely that the IR strobes would show up. The (certainly the last) version of software CAN detect when a jammer is being used. As the 2020 analyses the pulse width and duration it can detect transmissions that aren't it's own.
However, perverting the course of justice cannot be actioned in court, as justice has to be in progress, which it can't be of course - no evidence. Don't expect the police to be happy though, and they can make a lot of bother for you. impound the car etc etc.
Sweep errors don't stand up much either. A car travels 13.41cm per MPH during the time of a reading.
You can therefore get a sweep error of maybe 3MPH if it swept across the numberplate, but to be significant, the reading would have to be at an angle, and cosine error would be working in your favour anyway. The maximum you could get wouold be the length of the numberplate (maybe 4MPH) but the LTI would be reading almost 0MPH as the car would have to be at 90 degrees.
One thought would be to use fibre optics in the construction of the reflector in the plate, to emulate random travel paths. Basically, the LTI fires at the numberplate, but the reflector has fibres that may add tens of meters to the time of flight. Quite how you work that into a reflex reflector I don't know.
FYO.........
I earlier posted this on another thread if anyone is interested..........
Laser guns don't use doppler shift. The reflected light is doppler shifted of course, but the camera doesn't make use of this.
As your technically minded, he's how an LTI2020 works
There is a 905nm Infra red solid state laser module with deam divergence of approx 3mrad. It flashes 44 pulses of IR over a period of 0.3 seconds. This light is aimed at something very reflective, ideally the numberplate of a car which who's backing material has the same reflective properties of a 'corner cube' mirror, known as a reflex reflector (it reflects light in the direction in which it came to a tolerence of +/- 3 degrees) The reflected light pulses are picked up by an IR dependent resistor network behind refracting optics in the LTI 2020 and the time intervals are recorded into memory. The time intervals plotted against time create a gradient which directly correlates to the distance travelled by the point of reflection, and therefore the velocity. The LTI must recieve at least 30 similar reflected pulses to achieve a legitimate reading. It does this by applying the mathematical 'least squares' algorithm. (look on the net about 'least squares')
Way's to block an LTI2020.
Don't have a reflex reflector back plate on your numberplate. - illegal as it's a requirement of the number plate legislation.
Sandwich a sheet of IR filter gel between 2 of the layers when you have your numberplates made.
Not illegal. The legislation says that the numberplate should reflect light, and be easy to read. Say's nothing about IR.
Quick decelerating.
legal of course, and causes the LTI2020 to throw an error as the 'least squares' algorithm can't establish a grandient. (the gradient would be of a curved line as your velocity is changing quickly)
Put a lot of little spinning mirrors around the front of your car that spin in the airflow. This causes a lot of spurrious random reflections (the LTI2020 also looks as pulse width and shape to make sure it came from the same object (to try to eliminate sweep errors))
ACTUALLY............... why not put a load of reflex reflector material on your radiator fan?. just a thought.
The LTI2020 is quite a well thought out little s**t of a device. Matched only by the arrogance of their phone staff if you give them a call.
The best jammer of them all, if you can make one, is one that will measure your speed, and always return pulses that will make the LTI2020 read 30MPH, regardless of speed.
I'm sure you could do the maths. And you can buy laser modules!
just like IR remote controls, the lights is also modulated. not sure what frequency. Modulating it increases the range very significantly. For eg. a TV remote control LED only has a range of about 6 inches, but when modulated that increases to (theoretically) hundreds of meters. Installing IR's is like trying to drown out a very loud dog whistle with a bass guitar!.
Ideally, you want to try to make a pair of IR stobe lights, running at about 34kHz.
As I understand it, the CCTV units that the camera vans use filter out IR. (I've never yet seen the bright 'star' effect of the laser from a numberplate on any recording) so it's unlikely that the IR strobes would show up. The (certainly the last) version of software CAN detect when a jammer is being used. As the 2020 analyses the pulse width and duration it can detect transmissions that aren't it's own.
However, perverting the course of justice cannot be actioned in court, as justice has to be in progress, which it can't be of course - no evidence. Don't expect the police to be happy though, and they can make a lot of bother for you. impound the car etc etc.
Sweep errors don't stand up much either. A car travels 13.41cm per MPH during the time of a reading.
You can therefore get a sweep error of maybe 3MPH if it swept across the numberplate, but to be significant, the reading would have to be at an angle, and cosine error would be working in your favour anyway. The maximum you could get wouold be the length of the numberplate (maybe 4MPH) but the LTI would be reading almost 0MPH as the car would have to be at 90 degrees.
One thought would be to use fibre optics in the construction of the reflector in the plate, to emulate random travel paths. Basically, the LTI fires at the numberplate, but the reflector has fibres that may add tens of meters to the time of flight. Quite how you work that into a reflex reflector I don't know.
bryan35 said:
I've thought of a very simple way to confuse an LTI2020, that doesn't involve any electronics, jamming, filters, or anything that disguises the number plate. Going to do a few tests with a Helium Neon laser on my own car (so i can see it) and I'll let you know the results, and post my little idea when done.
Rotating reflector on the car?
bryan35 said:
However, perverting the course of justice cannot be actioned in court, as justice has to be in progress, which it can't be of course - no evidence. Don't expect the police to be happy though, and they can make a lot of bother for you. impound the car etc etc.
Is this correct? Haven't folks been arrested and threatened with a charge of attempting to pervert the course of justice for using a jammer?
Can this be why the prat in South Wales who was taunting police with his jammer was released with a caution?.........IIRC
8Pack said:
What would be the effect (if any) of the number plate being bent, either concave or convex by a small no. of degrees (hardly noticable). Would this not either scatter or focus the return beam? Maybe enough to make it unreadable?
No because of the corner cubes, they always reflect light back in the same direction
kevinday said:
What would be the effect (if any) of the number plate being bent, either concave or convex by a small no. of degrees (hardly noticable). Would this not either scatter or focus the return beam? Maybe enough to make it unreadable?
No because of the corner cubes, they always reflect light back in the same direction
Yes. Get rid of them...
HIYA! DELTAF! HOW'S THE RASH! 
Right, got them off! what do I do with them now? 
8Pack said:
What would be the effect (if any) of the number plate being bent, either concave or convex by a small no. of degrees (hardly noticable). Would this not either scatter or focus the return beam? Maybe enough to make it unreadable?
The photo I got back from a recent "alleged" offence (I'm fighting it BTW)was targeted mid way up the car bonnet so I don't think it matters what you do to the number plate.
right chaps, the answer it this.................
as the unit measures over 0.3 seconds, the reflective object travels approx 14cm for every 1MPH. The LTI checks the reflective beam amplitude and pulse shape to make sure they are consistant. Now imagine what would happe if you were to put a few CCM's (corner cube mirrors) along the front of your windscreen. The distance from the number plate to the windscreen is a fair way (1.5 meters on some cars), then if you put CCM's on the backs of your headrests, and on your mirros etc etc etc. Suddenly the LTI is bombarded with multiple direct reflections, all arriving at different times. ERROR 2 ERROR 2 ERROR 2.
as the unit measures over 0.3 seconds, the reflective object travels approx 14cm for every 1MPH. The LTI checks the reflective beam amplitude and pulse shape to make sure they are consistant. Now imagine what would happe if you were to put a few CCM's (corner cube mirrors) along the front of your windscreen. The distance from the number plate to the windscreen is a fair way (1.5 meters on some cars), then if you put CCM's on the backs of your headrests, and on your mirros etc etc etc. Suddenly the LTI is bombarded with multiple direct reflections, all arriving at different times. ERROR 2 ERROR 2 ERROR 2.
to add,
The light attenuation you get through the glass, is compensated for by the fact that CCM is much more reflective than the number plate. I've tried this.
Shone a Helium Neon laser at my car and the reflection from the number plate is like a very bright star, shine it at a CCM and the reflection is so bright you would lose your eyesight looking at it.
at 100m the 3mrad beam is about 30cm wide HOWEVER, what isn't so widely known if that the beam is astigmatised, narrow horizontal and high vertical (to stop exactly this problem occuring with multiple reflections from the headlights)
Multipath, you can't beat it.
The light attenuation you get through the glass, is compensated for by the fact that CCM is much more reflective than the number plate. I've tried this.
Shone a Helium Neon laser at my car and the reflection from the number plate is like a very bright star, shine it at a CCM and the reflection is so bright you would lose your eyesight looking at it.
at 100m the 3mrad beam is about 30cm wide HOWEVER, what isn't so widely known if that the beam is astigmatised, narrow horizontal and high vertical (to stop exactly this problem occuring with multiple reflections from the headlights)
Multipath, you can't beat it.
Interesting concept Bryan.
I fabricated my own front number plate some time ago now.
In my case i used normal space and height for the letters and plate size cut to the minimum.
The reflective back isnt reflective, its just tippex white, not the product, just the colour.
Then theres a sticky backing applied as normal.
The clear front perspex part is scotchbrited to remove the gloss.
Its totally unnoticable in daylight and tests done by Steve at UK Speedtraps website with lti on his own similarly prepped plates show it increases the distance you have before they get a lock by around 3-400 feet.
However, i still like your corner cube jamming idea, and will have a play with it myself.
I fabricated my own front number plate some time ago now.
In my case i used normal space and height for the letters and plate size cut to the minimum.
The reflective back isnt reflective, its just tippex white, not the product, just the colour.
Then theres a sticky backing applied as normal.
The clear front perspex part is scotchbrited to remove the gloss.
Its totally unnoticable in daylight and tests done by Steve at UK Speedtraps website with lti on his own similarly prepped plates show it increases the distance you have before they get a lock by around 3-400 feet.
However, i still like your corner cube jamming idea, and will have a play with it myself.
This is clearly an excellent idea, and there's an excellent chance that it can be made to work well.
But I bet the receiver circuits in the LTI 2020 have an automatic gain control and an amplitude threshold filter. The effect of this will be that a dimmer reflection can be ignored and the reading taken from the brighter reflection.
Therefore, the proper implimentation of this scheme involves a number of similar reflective sources.
Anyone got access to an LTI2020 for testing?
But I bet the receiver circuits in the LTI 2020 have an automatic gain control and an amplitude threshold filter. The effect of this will be that a dimmer reflection can be ignored and the reading taken from the brighter reflection.
Therefore, the proper implimentation of this scheme involves a number of similar reflective sources.
Anyone got access to an LTI2020 for testing?
safespeed said:
This is clearly an excellent idea, and there's an excellent chance that it can be made to work well.
But I bet the receiver circuits in the LTI 2020 have an automatic gain control and an amplitude threshold filter. The effect of this will be that a dimmer reflection can be ignored and the reading taken from the brighter reflection.
Therefore, the proper implimentation of this scheme involves a number of similar reflective sources.
Anyone got access to an LTI2020 for testing?
Contact Steve at UK speedtraps website, he has ALL the laser guns!
Tafia said:IIRC, the charge has been, "Obstructing a constable in the execution of his duty" - Streaky
However, perverting the course of justice cannot be actioned in court, as justice has to be in progress, which it can't be of course - no evidence. Don't expect the police to be happy though, and they can make a lot of bother for you. impound the car etc etc.
Is this correct? Haven't folks been arrested and threatened with a charge of attempting to pervert the course of justice for using a jammer?
Can this be why the prat in South Wales who was taunting police with his jammer was released with a caution?.........IIRC
They aren't actually corner cube mirrors, are they. I was under the impression that they were glass micro-spheres called "Ballotini" (trade name). These micro-spheres totally reflect the light but unlike CCMs they don't present their full projected area as reflectors but when closely packed in a resin matrix will present a myriad of pin-point like reflections. They're not so efficient as CCMs hence the dimmer reflection.
I like the IR filter sandwich idea best so far. Another one is to have the black areas of the letters actually transparent deep red acrylic that looks black to visible light but is clear to IR. If there is a Ballotini or CCM reflector behind the dark areas it won't show to the naked eye but will white-out an IR camera image to the same order of level as the surrounding visibly whaite background. None of this stops the detector working but it does stop the camera reading the number plate and having a photographic image of it.
I like the IR filter sandwich idea best so far. Another one is to have the black areas of the letters actually transparent deep red acrylic that looks black to visible light but is clear to IR. If there is a Ballotini or CCM reflector behind the dark areas it won't show to the naked eye but will white-out an IR camera image to the same order of level as the surrounding visibly whaite background. None of this stops the detector working but it does stop the camera reading the number plate and having a photographic image of it.
Gassing Station | Speed, Plod & the Law | Top of Page | What's New | My Stuff