Any Valentine 1 Users?

[joegr]

I suspect that the police IR laser systems can very effectively filter out most other sources of IR.
I once designed an IR based proximity detector to detect the presence of notes at the exit of a dispenser. To prevent the IR from sunlight (DC source) and the IR from room lighting (120 Hz source) from causing false triggers, I modulated my IR source at about 2 KHz. I then used a band pass filter on the receiver amplifier centered at 2 KHz. This made the receive circuit very immune to influence from anything other than it's on source emitter. I suspect that the laser systems do something similar, and I would guess that the laser jammers modulate their IR outputs to the same frequency as the lasers are using.

 

[Upstairs Chris]

I just can't see how radar would be that vibration sensitive though, since it can be used to clock a vehicle while the police car is in motion. I can see how a big truck can override the radar signal, and because radar will pass through plastic it usually only sees the bumper and engine block on a sports car.

This only reason I bring that up is that my crown vic has a shimmy at about 70 mph, and the vibration increases the time it takes for a radar to give me a speed.

On the driving lights, their reflectors can be used as a target, but (and this is supposition) the right kind of driving light when on would be a natural IR emitter, and might confuse your targeting laser. Do you notice any decrease in range at night vs daytime with the laser gun? If you do see a decrease in range, then it would point towards driving lights as an "innocent" laser jammer seeing as it would be outputting unmodulated IR and not the modulated signal your unit would have to use to be able to identify its own output. Enough unmodulated signal would mask your signal until the return provided a high enough signal to noise to be identifiable.

Zero impact. Driving lights do not impact the time it takes me to get a signal whatsoever, day or night. The shape of the light has a lot more to do with it, of course nice flat bumpers that are mostly vertical (ex: The LS) also will give readings qucikly, but metallic objects are the goal here. Front license plates are just to easy.

My uncle was a state trooper in WV for about 30 years before he retired, said that they were trained that when in doubt on which car was speeding, always pick the one in the passing lane.

Interesting, you should PM who your uncle is.
If I I am not sure I usually don't stop em. If I do, its warning only.

Another question for you: in Oklahoma they've been putting up metal cable fencing between the lanes on the highways. Does this have any effect on your radar or laser readings, since this has the potential of being a fixed reflective object within the line of sight of your device? I hate these things, one of these days a motorcyclist is going to hit one and get his leg cut off into several chunks.

No, the laser only will read what you put it on, it is a laser. If the beam has x spread at y distance that's all fine and dandy, but I have never aimed it at a car and picked up anything else, and if I am trying to get a reading on something the sight has to be dead on them, not just around them.

The reason lidar guns aren't used much is the cost. They are far more expensive than radar units http://tinyurl.com/bmjr9b4

 

[Telco]

Filtering can only block frequencies outside the desired bandwidth, but won't do anything for noise at the specific frequency. The laser will most likely have a modulation on it that the gun can pick up to identify its own output on reflection that I will call the gun signal. The gun signal must be of sufficient strength to overcome the noise floor in order for it to pick the signal up and be able to identify itself. If the noise floor is raised by a dumb transmitter at the same frequency, then the gun signal must be stronger in order to overcome the higher noise floor. You can equate this to a telephone call where you are in a quiet room. When you call another person in a quiet room that person can speak normally and you will hear them clearly. However, if the person you call is in a crowded stadium with a lot of noise, that person must scream into the phone in order for you to hear them, and you must scream into the phone for them to hear you. Even though you are speaking to the person, you must both overcome the local noise floor (the screaming crowd) in order to communicate. If you don't scream, and speak normally, your voices blend into the noisy background.

So, if you have an emitter that is transmitting a dummy signal at the same frequency as the laser gun, the laser gun must pick its modulated signal out of the noise created by the emitter. The closer the vehicle gets, the stronger the reflection from the gun, but also the stronger the noise. However, the gun signal's signal strength will increase faster than the noise signal because for every foot the noise signal travels, the distance the gun signal travels drops by 2 feet. There will come a point where the gun signal will be able to overcome the noise signal and the gun will be able to get a clean reading.

Here are a couple of charts that show what I am speaking of. They aren't specifically laser signals, but they do show what they would look like on an analyzer.

On this one, the long green line will represent the noise floor, and the spike would represent the gun signal with no interference. Lots of strength, lots of range.

Now say this represents the noise signal that the gun signal would need to overcome.

The gun would need to receive a minimum amount of signal over the noise signal in order to get a ledgible reading, otherwise it would not be able to detect its own modulated signal.

 

[Telco]

Interesting. I would have to guess that the lights aren't emitting enough of a signal at the correct frequency band to interfere with the laser gun then. And, PM sent.

 

[joegr]

Interesting. I would have to guess that the lights aren't emitting enough of a signal at the correct frequency band to interfere with the laser gun then. And, PM sent.

Halogen or other incandescent on a car will be DC (0 Hz) and very easy to filter out. HID will be somewhere in the KHz range, but will put out very little IR.

 

[Telco]

Halogen or other incandescent on a car will be DC (0 Hz) and very easy to filter out. HID will be somewhere in the KHz range, but will put out very little IR.

Actually, no. These bulbs do use DC, but create light by heating an element. This is a energy conversion process, therefore the input power method would be irrelevant to the output energy's form. As they produce heat and invisible light as well as visible light, they are extremely inefficient. Same with HID, it converts electrical energy into a plasma flux to emit light.

After some thought, the driving light as a jammer idea wouldn't work, the reason being is the amount of power needed to run the lights strongly enough to wash out the infrared signal. Power requirements for emissions increase logarithmically as a square of distance (if I remember correctly) so the amount of power needed to jam at 2000 feet would be enormous without focusing. Less power would be needed to power a focused jammer at the right frequency, but it would still take a lot of power as you'd have to flood the road in order to jam the signal since you'd not know where the gun would be. The only other way would be a tracking scanner that could pick up the laser gun's signal before it can hit you, lock on and track it while jamming. A split second burst isn't going to be nearly enough for that, the laser would have to operate in a continuous mode for it to work.

You know, come to think of it, if the police are targeting headlights you don't have to know where they are, because you will know where they are aiming. An LED that emits 904nm with sufficient power might interfere long enough to let you slow down, but you'd better have a kill switch for the LEDs so their second reading will work. If they can't get a reading on you from 200 feet, but they can read other cars, guess who's going to get the rubber glove treatment? Of course you will need to connect them to the detector itself so they come on instantly, and only operate when the detector is picking up a laser signal. Otherwise you'll be triggering everyone else's detector, and triggering your own every time you pass a reflective sign.

Probably the most effective defense would be to dampen the car's ability to reflect infrared light back along a straight line.

 

[Upstairs Chris]

I would totally stop a car for jamming my laser. It's not illegal or anything, I'd just be very interested.

 

[joegr]

Sorry, but I (and some of my professors) have to disagree with you there. You are confusing the wavelength of light with the frequency of the modulation of the light. These are two very different things.

I'm not saying the halogen blubs driven by DC don't emit IR, they do. I'm saying that the IR is modulated at 0 Hz. As such, it will easily be filtered out by the speed gun that is looking for IR modulated at say 20/40/60 KHz.

 

[Telco]

Sorry, but I (and some of my professors) have to disagree with you there. You are confusing the wavelength of light with the frequency of the modulation of the light. These are two very different things.

I don't follow? I assume this is on the power source you were saying before, which would be irrelevant to the light output.

 

[joegr]

I don't follow? I assume this is on the power source you were saying before, which would be irrelevant to the light output.

When you turn on a flashlight, you get white light (and some IR and other things), but it is all DC (0 Hz). When you turn on a florescent room light, you get white light (and some IR and other things), but it is all at 120 Hz (in the US). (Yes, the AC is 60 Hz, but since there is no negative light it becomes 120 Hz out of the light.) You can test this by moving your hand quickly in front of you. You will get a stop motion sort of effect due to the 120 Hz strobe rate of the light. You can't do that with the flashlight.

Your IR TV remote modulates its IR output at about 40KHz. This is so that the receiver can easily filer out the IR from the sun and from the room lights. In all three cases, the IR is the same wavelength, but it is modulated at different frequencies (40KHz, 0 Hz, and 120 Hz). I can take another remote at 40KHz, and use it to jam the signal from your remote. If I just used an IR LED driven at DC, it wouldn't jam your signal, even though it would be at the same wavelength and same brightness.

 

[Telco]

I follow what you are saying now.

When you turn on a flashlight, you get white light (and some IR and other things), but it is all DC (0 Hz). When you turn on a florescent room light, you get white light (and some IR and other things), but it is all at 120 Hz (in the US). (Yes, the AC is 60 Hz, but since there is no negative light it becomes 120 Hz out of the light.) You can test this by moving your hand quickly in front of you. You will get a stop motion sort of effect due to the 120 Hz strobe rate of the light. You can't do that with the flashlight.

A flourescent bulb also doesn't work in the same way as an incandescent either though. A flourescent bulb is sending a pulse through a vapor to produce light whereas an incandescent is heating an element to produce light. Power frequency would matter on an incandescent but not on an incandescent. In fact, you can hook 10 12V batteries together in series to get 120V, then light the AC120 bulb up. I'm not 100 percent sure on the plasma bulbs as to whether they are like flours or incans though. I just know the basics about them, they create a plasma arc to make light.

Your IR TV remote modulates its IR output at about 40KHz. This is so that the receiver can easily filer out the IR from the sun and from the room lights. In all three cases, the IR is the same wavelength, but it is modulated at different frequencies (40KHz, 0 Hz, and 120 Hz). I can take another remote at 40KHz, and use it to jam the signal from your remote. If I just used an IR LED driven at DC, it wouldn't jam your signal, even though it would be at the same wavelength and same brightness.

Actually, it will jam the signal. Anything that raises the noise floor in the frequency range of a signal will jam the signal once the noise floor is raised sufficiently to kill signal to noise. It does not neet to match your modulation, it just needs to drown your signal. The stronger signal will overwhelm the weaker signal, and modulation will no longer matter.

I actually have a pretty strong background in this stuff, worked military communications satellites for 6 years and occasionally had to deal with signal jamming from various sources. A strong signal of the same frequency that overrides your modulated signal absolutely does not need to be modulated and absolutely will kill a modulated signal. If you pulled the modulator out of the same model laser that Chris uses, then fired it at his gun from a couple of feet away while he was trying to get a reading off an oncoming car, if he got a reading off the car at all it wouldn't be until it was practically passing him because the unmodulated signal at the same frequency would drown out the modulated return signal for his gun.

 

[Upstairs Chris]

I hate to interject in this conversation that is admittedly above my head. However, I think its relevant to point out again that aiming my lidar gun at a headlight does not in anyway shape or form alter the readings. Day or night, HID's or not.

 

[joegr]

Okay, I think I'll drop this one before I resort to indicating my engineering degrees, job title, or test results.

A few last points.

An incandescent bulb powered by DC puts out pretty much pure "DC" light. An incandescent bulb powered by AC puts out mostly "DC" light due to the thermal momentum of the filament. However, there is (and I guess you don't believe this) a 120Hz ripple to the light that can be detected and measured. I have used separate examples to keep this simple, but apparently not simple enough.

Why don't you try some of the things that you say are and aren't possible? I actually have.

You can only jam a modulated transmit/receive scheme (like the remote example) with a very strong DC source. Were you using an IR LED that was actually a stronger source than sunlight? It's possible but rare. If you want to jam with a normal IR LED such as is in a TV remote, you are going to have to modulate it to close to the same frequency as the remote receiver. Try it sometime.

 

[joegr]

I hate to interject in this conversation that is admittedly above my head. However, I think its relevant to point out again that aiming my lidar gun at a headlight does not in anyway shape or form alter the readings. Day or night, HID's or not.

I have not disagreement with that, and I was trying to point out why.

 

[joegr]

... If you pulled the modulator out of the same model laser that Chris uses, then fired it at his gun from a couple of feet away while he was trying to get a reading off an oncoming car, if he got a reading off the car at all it wouldn't be until it was practically passing him because the unmodulated signal at the same frequency would drown out the modulated return signal for his gun.

If that is really true, then the receiver was badly designed. I generally design with a goal of having the receiver have a dynamic range that can handle up to three or four times the level of desired signal. In that case, the modulated and unmodulated beams would combine and the receive signal would be at 1x with the modulated part pushing it to 2x. The band pass filter would still remove be able to remove the unmodulated part and the modulated part could still be detected. You are correct that if the unmodulated signal were much stronger and could saturate the receiver, it would no longer be possible to see the modulated signal and it would be jammed.

Was it specifically IR signals in daylight that you were dealing with, or was it RF?

 

[Telco]

It was RF that I worked with when in the military, then moved on to fiber optics. Not IF, didn't get into that until I moved into fiber optics after the military. Admittedly I was a tech and am not an engineer. Just the guy that worked on it, and had to fix it when it broke, and figure out why it wasn't working including when we were being jammed.

And, I don't have access to any test gear anymore.

So what is it that you actually design? Incidentally, I've been enjoying the debate, and am always open for correction, although it is now my weekend and I may or may not respond back for a day or two.

 

[joegr]

Most of my design work is in digital microprocessor design, but I've done analog, telecomm, IR, various sensors, motor control, ...

 

[Upstairs Chris]

I have not disagreement with that, and I was trying to point out why.

I know you didn't.

 

[Telco]

Neat. Sounds like you'd know what you are talking about then.

Those laser guns, at least the ones, I saw when I looked them up, were DC operated, with some of them operated with a couple of what looked like D cells. Chris would be able to clarify that. Based on that, I wouldn't think the AC/DC issue would matter since both would be DC.

Since they are battery operated, that would mean that the laser gun's signal isn't that strong to begin with. So, a jammer really wouldn't need to be that powerful then, although it would need to be quite a bit more powerful than the laser gun.

On the satellite jamming, it is done through saturation. The jammer will pump enough power at the satellite, it's just like putting a legitimate signal up except it's nothing but transmitted power, no modulation. Once the signal pushes the noise floor higher than the legitimate signals, they are gone and communications are lost. I wouldn't think it would be much different in the near infrared range. Thoughts?

 

[joegr]

It doesn't matter that the guns are DC powered. Inside are electronics to modulate the signal. Generally, they do pulses instead of AC, but the result is pretty much the same. They probably even encode a unique ID (unique per gun) into the modulation.

 

[Stopsign002]

Lol reading this is like having a discussion with my father (hes a nuclear physicist).

I love the technical information, thanks for taking the time to post it all. As much as just knowing that something works is nice, its much more interesting knowing why it works

And to throw in my 2 cent, scattering the signals is definitely going to be your best defense over trying to over power them, at least that would be my thought based on what physics I know

 

[Telco]

It doesn't matter that the guns are DC powered. Inside are electronics to modulate the signal. Generally, they do pulses instead of AC, but the result is pretty much the same. They probably even encode a unique ID (unique per gun) into the modulation.

So the modulation survives even if the jamming signal is stronger than the modulated pulse? How would that work with IF? Admittedly my main experience with jamming is with RF, but I've never seen a modulated pulse survive a jamming signal. The receiver is looking for the pulse at the set frequency and bandwidth, but can't pick the modulation out of the stronger jam signal.

Stopsign - after this discussion I'm tending to agree now. I figured it would be easier to build a jammer that would give the laser gun less range and you more warning since scatter requires either an absorbing material like a car bra or major bodywork to change the forward angles of the vehicle, but it's starting to look like redesigning the front clip and painting the car matte black would be easier. Not that I intend to do that, of course, as that would just look and be silly.