Nothing about laser jammers on Wikipedia

[Roadghost]

So I was just wondering about some of the specifics of laser jammers, particularly diodes vs LED's, what type of laser is used by police (nm, green, red, white, etc.) and what type of diodes are used to jam them. The whole thing is a dark science to me.

There's this pulse per second thing on GOL and nothing to explain how it relates to jamming and error codes. And there's the little matter of how to stop error codes, or if that's even possible.

We need some of the manufacturers to write up a really good chapter for Wikipedia explaining what their devices are and how they work. This will dispel some of the skepticism around these products.

It's also free indirect advertising for jammers in general.

[AirMoore]

That would suck IMO...


If you do enough searching around here... you should find all the info you need.


Wikipedia is the last place we want laser jammers being shown, unless it says they dont work... I would have to say that in no time after they go on wikipedia would it be before many more states ban them, let alone federal bans on them.

[jimbonzzz]

Airmoore brough up some very valid points. Also, a Wikipedia article would need to be very high-level, and probably wouldn't answer many of your questions.

So I'll try to fill you in, if you can follow...

Most police laser is 904/905nm infrared laser. The laser diode used in the guns is commonly around 50 Watts peak power, though could be more or less.

"LED" jammers usually use 8 infrared LED's per transponder. These LEDs are commonly at 870nm, and can jam the 904/905nm guns because they're close enough that they will still be received by the laser guns, and the LEDs also emit closer to 904/905 when they heat up. A transponder using several LEDs will still have much less power than a transponder using laser diodes.

"Laser Diode Jammers" usually use one laser diode per transponder, though recently some jammer makers have made designs with two laser diodes per transponder. These laser diodes are 904/905nm with 10-100 Watts peak power, depending on the jammer. It is important to note that the jammers do not usually use optics to the extent that the laser guns do in order to collimate the beam, thus the jammer beams spreads out more to ensure wide coverage.

As far as how the guns are jammed, it works like so:

The laser guns are "gated", which means that they'll only accept a pulse and use it for speed calculations when they're expecting to receive a pulse. The guns are only expecting to receive a pulse betwen the time it sends out it's pulse, and before that pulse is reflected back. Any jamming pulses must be received in this time window too, in order to have any effect. Once the gun's own pulse is reflected back, all bets are off: the gun uses it's own reflected pulse for calculations, and doesn't accept any pulses until it sends out another pulse.

For example, a Kustom ProLaser III sends out 200 pulses per second, or one pulse every 5000 microseconds. At 1000 feet, the "time of flight" of the gun's pulse is 2 microseconds (about 1 foot per nanosecond for total travel of 2000 feet). So, any jamming pulses must be received by the gun in that 2 microsecond window. If a jamming pulse reaches the gun during the next 4998 microseconds, it has no effect at all and is essentially ignored by the gun. Then, the cycle repeats for the next pulse.

How do the jammers get a pulse into this narrow time window? The jammers receive a few of the laser gun's pulses, and time between them. Then, they are able to "predict" when the next pulse from the gun will be received at the jammer. A number of nanoseconds before the predicted pulse is expected to be received, they send out one or more jamming pulse(s). This ensures that a jamming pulse is received at the gun before the gun's own reflected pulse is, and is during the time window where the gun will accept a pulse and use it for speed calculation. Since the jamming pulse makes it back to the gun first, the gun's own reflected pulse is ignored.

Jammers recognise individual guns based on the pulse rate, this is called using a "look up table". With a look up table, jamming can be customized for the specific laser guns. This is done so that pulse timing can be custom-tailored for each laser gun, for optimal jamming and avoiding jam codes. In addition to a "look up table", some jammers use a default algorithm to attempt to jam unrecognised guns. Not all jammers use a default algorithm.

The laser guns generally need 30-60 consistent pulses in order for a speed reading to be displayed. In general, the pulse timing in the time window can varied slightly for each pulse. This varies enough so that they do not correspond to any speed, so no speed is displayed. But other techniques might also be used, such as discussed below.

As for avoiding jam codes: the guns use different schemes to detect jamming. In order to attempt to avoid jam codes, a few different techniques are used, such as precisely timing jamming pulses in the time window to fake conditions which might be present during regular targeting. These conditions might cause other operational error codes to appear on the gun, but codes which do not indicate jamming. Another method might be to limit pulse amplitude in certain situations.

There was an older jamming technique, used in the Lidatek LE-10 and Target LE-850. Instead of precisely timing jamming pulses with incoming pulse, these jammers first detect the laser, and then transmit jamming pulses at a very high frequency, generally 4 MHz. At this frequency, there is a pulse transmitted every 246 nanoseconds. This ensures that there will always be at least one jamming pulse which makes it into the time window for the gun, as long as the vehicle is about 125 feet away from the gun or further (light travels at about 1 foot per nanosecond, if the vehicle is 125 feet away the time of flight of the gun's pulse is 250 nanoseconds). This scheme should successfully jam all guns. But, there are some drawbacks. This scheme will definitely cause jam codes on the guns. And, the laser diodes are not rated to operate at 4 MHz, but jammer makers found that they could operate at this frequency for a very short time without burning up. So, jamming is only possible for a short period of time, generally a number of seconds. After that, the laser diode must cool before it can jam again.

Well, I hope this covered it :wink:

Jim

[ELVATO]

Wow. I actually understood that Awesome summary of jammers. I say this be a sticky.

[ahmadr]

You should create the wikipedia article. That was very nice writing

[lilmikey]

I dont want anything about laser jammers on wiki, keep it underground

People that look will find what they are looking for in the end.

[Phillip559]

Wikipedia has a reputation for being full of bull**** since anyone can author stuff.

College professors hate it because kids will cite it like its authoritative when its really not.

Just a warning: Don't believe everything you read on it.

Also, i agree this should be kept underground. Let the people come to the forum and learn. I am in the very process myself

[lukenosewalker]

Every time I read about the job a jammer has to perform, I am amazed at the level of sophistication. It doesn't seem like an easy task to perform, but some do it quite well.

[TSi+WRX]

Superb!

:arrow: Sticky?

[Roadghost]

Interesting Jimbonzz. It may take the ship's computer to solve this.

I suggest the best way to avoid diode overheating is to have sequentially timed diodes within the transponder, such that when one shuts off due to heat, another is timed to come on.

I didn't see a jammer that was successful at avoiding jam codes in the GOL tests. Didn't see much on the reliability of the gun's jam codes either, as in what makes them falsely display error codes?