# Thread: jammer detection how?

1. ## jammer detection how?

I was thinking many times, and I don't understand, how can lidar detect jammer? If jammer pulse is first als lidar pulse, then no jammer error? If pulse from jammer is after lidar pulse then is like without jammer. So how lidar can detect jamming? and it is importantly pulse duration? I mean 20-60ns? I think that if lidar use pulse 20ns duration, and jumming pulse is 30ns , then lidar wil detect jamming. I'm wrog?
sorry for bad english. :P

2. If the jammer is putting out pulses which are 1 to 1 with the lidar then it would be very hard to detect the jammer. Unfortunately this is not always the case.

Once the gun is receiving more pulses than it is putting out it is simple to conclude that there is probably jamming going on.

3. "Once the gun is receiving more pulses than it is putting out it is simple to conclude that there is probably jamming going on."
I think that first pulse lidar can receive only (in the time when lidar send pulse and wait for back pulse)! Then all others pulses is like no pulses. Or I'm wrong? So how can lidar know that jamming is active?

4. easy way to detect a jammer is use a IR enhanced camera, you will see the diodes light up

5. If you will say, that not 1 pulse is recaiving (in this time window) so how it is working in jammer that work without error code ? Minimum 1 pulse is from jammer and minimum 1 pulse is after jamming pulse orginal that was from lidar (reflected). 2 pulses minimum...
Or lidar calculate all pulses, only first pulse use for speed calculation?

6. Originally Posted by ginasas
"Once the gun is receiving more pulses than it is putting out it is simple to conclude that there is probably jamming going on."
I think that first pulse lidar can receive only (in the time when lidar send pulse and wait for back pulse)! Then all others pulses is like no pulses. Or I'm wrong? So how can lidar know that jamming is active?
They only compute on the first pulse received after transmission but can receive all pulses. The detector doesn't have a clue about 1st 2nd or 100th. It only recognizes IR radiation. How the gun processes them is up to the designers. Any engineer designing one of these guns would probably count pulses since it is kind of a freebe and would certainly detect any attempt to jam the gun with any system that wasn't one to one within pulses sent out.

I'm just guessing here since I don't have a gun but having designed a lot of electronics over the years it would seem any decent engineer would think of this as a no or very low cost method of detecting jamming. All the required hardware is already available to do the real job of the gun.

7. Originally Posted by ginasas
I was thinking many times, and I don't understand, how can lidar detect jammer? If jammer pulse is first als lidar pulse, then no jammer error? If pulse from jammer is after lidar pulse then is like without jammer. So how lidar can detect jamming? and it is importantly pulse duration? I mean 20-60ns? I think that if lidar use pulse 20ns duration, and jumming pulse is 30ns , then lidar wil detect jamming. I'm wrog?
sorry for bad english. :P

Pulse duration does not matter, only the leading edge is used. This is why jammers such as Blinder ZR3 etc are able to jam successfully using LED's with longer pulse durations. Especially at long range when the beam diverges, portions of the pulse might strike a sloping surface, differect objects etc. So, parts of the pulse return to the gun faster than others, having the effect of stretching the pulse, or even multiple pulse returns. I'm sure that to a point, the gun will compare thresholds to determine which pulse should be evaluated as the actual target. So, I don't think that simply receiving extra pulses by itself is necessarily indicative of a jam either. Even with the current jammers that are able to avoid codes, the gun always receives more pulses than it normally would: the reflected pulse that it sends out, and also the jamming pulse.

I think the current US guns LTI and Stalker indicate jamming if they detect a high-intensity light source. So, on some occasions sunlight can cause a jam code. I don't know about Laser Atlanta since nobody that I know has experience with their new Jammer indicating feature yet. I would think that most jammers could easily avoid jam codes on these guns, with the exception of the LE-10/LE-850, which emit a lot of light.

Here is a description of the method used by LTI:

The invention further advantageously provides a laser speed detector that includes circuitry to detect when attempts are made to evade speed detection by a laser speed detector.

By indicating to the police that a vehicle is transmitting high-intensity light energy, the officers can deduce that the operator of the vehicle is likely attempting to evade speed detection. Such an indication would also provide the officer with an identifiable error message if the light energy generated at the vehicle is of great enough amplitude to prevent accurate speed determination. Such an indication would also allow the sensitivity of the laser speed detector to be altered to ignore the high-intensity light energy.

According to the invention, therefore, a countermeasure detecting circuit and an associated method detect countermeasures taken at a target to impede speed measurements taken with a laser speed detector. The laser speed detector is operative to transmit light energy to the target and to receive light energy reflected from the target. Light signal detecting circuitry detects light energy of wave lengths corresponding to wave lengths of the light energy transmitted by the laser speed detector. Received-light signals of values representative of the levels of light energy of the selected wave lengths are further generated. A comparator circuit is coupled to receive the received light signals generated by the light signal detecting circuitry. The comparator circuit compares the values of the received light signals with a threshold signal. The threshold signal is of values representative of levels of background noise of light energy typically received by the light signal detecting circuitry. Comparison signals are generated responsive to such comparisons. The comparison signals are of values representative of times in which the light energy detected by the light signal detecting circuitry exceeds levels of background noise by at least a selected amount. Control circuitry is coupled to receive the comparison signals generated by the comparator circuit. The control circuitry detects when the comparison signals are of values indicative of countermeasures taken at the target.
But of course as many of you have indicated, the manufacturers have any number of methods available to them, I don't know what methods might be used in other guns...

Jim

8. I didn't mean to imply that anything other than 1 to 1 would indicate jamming. However any jammer that is just spitting out pulses without regard to what it's sensors are receiving would certainly be a candidate for a a gun thinking it is being jammed. In particular those which just send out a high frequency pulse stream or those who look up a gun type and try to send returns early would be detectable, the latter only if it didn't stop sending at the same time the gun stopped transmitting.

The only reason I have an interest in this is I am going to get a jammer. Since I live in a state where both RD's and jammers are illegal it is imperative that the LEO's can't detect either as a car search would net me a double header. The STI pretty much has the RD part covered since the RDD's can't detect it and in my particular car it is about invisible from the outside unless you press your nose against the windshield.

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