# Thread: How laser jammers work ?

1. ## How laser jammers work ?

do they get the laser gun signal and do not sent it back to laser guns to get measurments?
Do they sent several speeds to laser gun and get confused ?
How do they work ?

2. alls that I know is that it takes the pulse rate of the gun off at first and then it matches that signal and overpowers the gun so that it doesnt recieve its own speed sensing pulses off the car......... I dont know the absolute specifics but thats the basics behind um

JIM WHERE ARE YOU????

3. First: the laser gun sends out a series of pulses. Each pulse reflects off the target vehicle and back to the gun, and by measuring the "time of flight" of the pulse, the gun can obtain a distance reading. By taking a series of distance measurements over time, a speed reading can be calculated and displayed.

In a nutshell, laser jammers work by first receiving pulses from the gun, and then timing the jamming pulses in such a way that the jamming pulses are accepted by the gun as it's own reflected pulse.

There is a very narrow time window to get a jamming pulse to the gun when it will be accepted and used for speed calculation. The gun only accepts and uses a pulse if it is expecting to receive one, which is after it sends out it's own pulse, but before it receives the reflected pulse back. Once the gun receives it's reflected pulse back, it isn't expecting a pulse until it sends out another pulse. So, any pulses received during that time are simply ignored, not used for speed calculation by the gun, and thus no jamming effect.

To get jamming pulses into this time window, the jammer first receives a few of the gun's pulses, with which it can calculate the pulse rate and thus "predict" when the next pulse will be received. Then, it can send a jamming pulse (or series of pulses) a number of nanoseconds before it expects to receive the next pulse from the gun. This jamming pulse makes it back to the gun before the gun's own reflected pulse, and is accepted by the gun as it's own reflected pulse, and used for speed calculation.

Once the time window is calculated, the jammers might use a variety of techniques on different guns. The application of the pulse or pulses in the "window" can be customized for most effective jamming of the specific guns, and avoiding jam codes. For example, perhaps the most obvious application is that each jamming pulse might have random delays, so that wildly different measurements result that do not coincide with any consistent speed, so none is displayed.

A couple of the old jammers, the Lidatek LE-10 and Target LE-850, do not precisely time their pulses like todays jammers do. They send pulses at a very high frequency of 4 MHz (patent says 2 but I was told 4 by Lidatek). This means that there is a jamming pulse every 250 nanoseconds. Since light travels at roughly 1 foot per nanosecond, this means that at least one jamming pulse would make it into every time window and be accepted by the gun, as long as the vehicle is more than 125 feet away from the gun. Once the target vehicle is closer to the gun, say 100 feet, the time window would be only 200ns, and since jamming pulses are sent out every 250ns, they might miss the time window so some pulses wouldn't get jammed.

Jamming every single pulse from the gun isn't necessary, it only needs to jam enough pulses to prevent a speed reading. Although in theory a speed could be calculated with only two distance measurements, in order to be truly accurate the gun needs a number of consistent pulses to display a speed, generally 50+.

Jim

4. jim...

then in what way does being a laser diode "better" than using LEDs in terms of jamming capability?

in another words, how does the fact of being "more watts" play a role in jamming capability and out performs the LEDs?

another question is that..
for UTL laser guns....theoretically they r not much differ in terms of specification.
but what makes 200LR more difficult to jam in comparing to say 100LR? they all operate in the same pulse rate, aren't they? then why some jammer fail to jam 200LR but has no problem in jamming 100LR?

thanks so much...

5. First, thanks again to The Professor for his lesson! I'm learning a lot from your posts (so much so that I should probably do a retroactive search on your past posts!).

1919 - I don't want to speak for The Professor, but here's something that he'd posted as an answer to one of my questions:

I don't think that will answer your question completely, but it should be of-interest.

6. Originally Posted by 1919
jim...

then in what way does being a laser diode "better" than using LEDs in terms of jamming capability?

in another words, how does the fact of being "more watts" play a role in jamming capability and out performs the LEDs?
It isn't difficult to equate power=performance. The guns have a threshold for what is received, and at least some adjust it dynamically. I believe with the Ultralytes several pulses are used specifically for this purpose. In the case of LED jammers, at some point the gun's reflected pulse from the vehicle becomes stronger than the jamming pulses from the LEDs at which point the gun begins to accept the real reflected pulses instead of the jamming pulses = punchthrough.

Originally Posted by 1919
another question is that..
for UTL laser guns....theoretically they r not much differ in terms of specification.
but what makes 200LR more difficult to jam in comparing to say 100LR? they all operate in the same pulse rate, aren't they? then why some jammer fail to jam 200LR but has no problem in jamming 100LR?

thanks so much...
The only difference between a 100LR and a 200LR is that the 200LR has an inclinometer. I don't know of any cases where a jammer fails to jam a 200LR but can jam a 100LR, unless one is 125pps and one is 100pps, which should answer your second question: most are 125pps, but some are 100pps. For more info on the 100pps version see here:
http://www.guysoflidar.com/lti-ultralyte.html

BTW welcome to the forum

7. ## LED vs. Diode

Originally Posted by fulcrum
Originally Posted by jimbonzzz
Originally Posted by TSi+WRX
Follow-up question:

Does "more power" translate into "brightness?"

When I viewed the diodes on my LPP's heads, activated by the Laser Tester sold on Roy's site, through my standard digicam, it seemed not nearly as bright as the LEDs on my ZR3's heads.

Sorry for the stupid question - I'm a biological scientist. ops:
Well, it's "peak power"...
Laser diodes can handle much shorter pulses than the LEDs can. The laser gun's pulse duration is about 20-50ns, so laser diode jammer pulses are probably a similar duration. But the "rise time" for most LEDs is many times that. So, the LEDs are "on" for a much longer duration and a larger percentage of time, probably making an LED jammer appear to be "brighter". But it is the peak power that makes the difference. To jam the gun, only the leading-edge of the pulse matters, which is why LED jammers are still able to jam.

Jim
I'd like to add to that:

The receiver of a lasergun has a filter (high-pass ) that makes it less sensitive to slower rise time signals (Like LEDs). In my experiments with a Jenoptik LaserPatrol, this turned out to be a very important factor. (I connected a scoop to the receiver circuit of the JenOptik and measured how the receiver detects laserpulses)
Originally Posted by go.mouse
Blinder, Escort Zr3, Bel LP905 all use LED's. Diode jammers are Lidatek, Laser Pro Park, and AL G8. Lidatek laser diode is much less powerful than the other two.

So basically, diode is the way to go for front and rear attacks then. Is the M20-40 diode then? Also, if wanted total protection, what jammer is the best :?
RR

8. I propose that the admins make this a sticky. Or massage the info into an existing sticky.

9. thanks for the fast reply...
and thanks for the warm welcome...
i've been under the water for such a long time and finally pop out to breath for the first time....

Originally Posted by jimbonzzz

It isn't difficult to equate power=performance. The guns have a threshold for what is received, and at least some adjust it dynamically. I believe with the Ultralytes several pulses are used specifically for this purpose. In the case of LED jammers, at some point the gun's reflected pulse from the vehicle becomes stronger than the jamming pulses from the LEDs at which point the gun begins to accept the real reflected pulses instead of the jamming pulses = punchthrough.

The only difference between a 100LR and a 200LR is that the 200LR has an inclinometer. I don't know of any cases where a jammer fails to jam a 200LR but can jam a 100LR, unless one is 125pps and one is 100pps, which should answer your second question: most are 125pps, but some are 100pps. For more info on the 100pps version see here:
http://www.guysoflidar.com/lti-ultralyte.html

BTW welcome to the forum
so can u say that "power" is not everything? or at least not the major part? Cuz lately everyone is just so emphasizing in diode power>>>LED power, and therefore = JTG, leaving the impression that "power" is everything , and "power" is the way to go instead of the LEDs. Or can you say that in order to JTG, besides the software part, the power of the jammer signal must be >>than the gun's own signal in order to be accepted into the gun, correct?

but how about the other parameters that you have mentioned before such as "rising time", "peak power", "pulse width and duration"?? How do these factors affecting the jamming capability and thus makes laser diode a better candidate?

i've seen blinder performs well against 100LR, but had a high PT against 200LR. I think even in Roy's SML 2006 jammer test also showed that blinder had PT vs. 200LR. It seemed that "inclinometer" is not the only difference between those two models i think.
but your reply gave me some thought though. correct me if i am wrong, but I did notice that the lenses on 200LR have blue coating, and 100LR have gold coating. Maybe these kind of different lenses as you have mentioned increase the receiving "threshold", and those making some jammer PT. Thus "power" in this case would be very important? what do you think?? Or could it be something else ? softwarewise??

10. Great info
thanks JIM

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