# Thread: Mounting jammer sensors flush or setback - how much of a difference does it make?

1. ## Mounting jammer sensors flush or setback - how much of a difference does it make?

I have been looking at install options for a LI system. One option I've considered is under a ledge that is formed by the top surface of an air intake. Most recommend that the sensors need to be flush with the front edge of the ledge or protrusion and this would work. However, if I could set the sensor back just an inch or two, it would be almost invisible to a person standing near the car (ie a LEO).

So then what's wrong with the reasoning in this thread copied from e90post.com (can't post a direct link as I'm new but you can google a phrase from it)?

The total beam divergence for the Osram SPL PL90_3 that the LI (and probably other diode jammers) uses is 11 (+/- 5.5) degrees vertical and 25 (+/- 12.5) degrees horizontal. At those angle, power output is half the peak. At twice that angle, the output is virtually zero:

Therefore, if your jammer heads (or input and output diode locations) have +/- 11 degrees clearance vertically, and +/- 25 horizontally, there is no point in wanting extra clearance.
My simple calcs (and bear with me as the last science class I took was high school physics so I wouldnt be surprised if there were some obvious mistake here):
- Say you want to mount the sensor set back slightly under a ledge as described above
- The height of a LI jammer sensor unit is 0.56" per their website. Thus assume the center of the diode is 0.28" from either the top or bottom of the sensor.
- Now imagine a right triangle formed by an imaginary line from the diode to the mounting ledge and perpendicular to the ledge (one leg), the outer edge of the spreading laser beam (hypotenuse) and the line defining the setback from the front edge of the ledge (other leg)
- If the maximum clearance angle needed is +/- 11 degrees, then the angles of the right triangle would be: 11 degrees / 79 degrees
- We also have a known side length which is for the first leg (between the diode and the ledge / mounting surface or the height of the sensor = 0.28")

Based on an online triangle calculators (why didn't they have these when I was in school), the diode in the sensor could be recessed about 1.44" back front the protruding edge of the ledge before diode output was impacted. At this setback, a person of average height would need to be standing 11+ feet away to see any part of the sensor and much further back to see the centerline of it.

What's wrong with this thinking?

2. ## Re: Mounting jammer sensors flush or setback - how much of a difference does it make?

Your overlooking the other half of the equation, RECEPTION! You want them to protrude ever so slightly to address wide and high axis LIDAR attacks.

Cliff

3. ## Re: Mounting jammer sensors flush or setback - how much of a difference does it make?

Interesting, but it seems since the sensors are mounted in-line with the diodes there would be no chance of actually jamming a signal received from this wide / high axis?

In other words, even if the sensor can "receive" from a wider angle location, since it is basically set in-line with the diode, there is no way the diode can emit light in a wide enough pattern to jam the laser signal. If this is the case, the effectiveness is the same as a radar detector (ie you know you are about to get a ticket but there is nothing you can do about it).

What am I missing?

4. ## Re: Mounting jammer sensors flush or setback - how much of a difference does it make?

There is no culminator (optical device used to focus light) on the transmitting diode unlike a LIDAR gun that has a lens to focus it's beam so when the beam leaves the sensor, it's divergence is very wide and expands quickly the further down range it emanates to provide adequate jamming to address wide axis and in the case of the HP, high axis attacks.

Cliff

5. ## Re: Mounting jammer sensors flush or setback - how much of a difference does it make?

The bottom line is, they won't work like that. Go to a testing some time. You will see.

6. ## Re: Mounting jammer sensors flush or setback - how much of a difference does it make?

what i envision is some kind of 'retractable' sensors.

ie. you get pulled over, flip the switch, and the sensors retract from view

7. ## Re: Mounting jammer sensors flush or setback - how much of a difference does it make?

Probably the best compromise between stealth and performance is to have the heads perfectly flush with the grill or whatever it's mounted to.

But since most grilles are curved, perfect flush doesn't mix with "level and square". In this case, mounting such that the outer edge of the head sticks out slightly (this is the reception end) and the inner edge is recessed slightly (emitting end) gives a decent compromise.

As long as you're talking, say, less than 1/4 inch recessed on the inner edge you should be ok with overhead shots. If they're shooting so close from an overpass that your heads can't see it, chances are you're too close for them to get a good reading anyway.

8. ## Re: Mounting jammer sensors flush or setback - how much of a difference does it make?

Originally Posted by Laser-InterceptorUSA
There is no culminator (optical device used to focus light) on the transmitting diode unlike a LIDAR gun that has a lens to focus it's beam so when the beam leaves the sensor, it's divergence is very wide and expands quickly the further down range it emanates to provide adequate jamming to address wide axis and in the case of the HP, high axis attacks.

Cliff
This makes intuitive sense for your HP sensors, definitely (where there is a second diode mounted so the wide dispersion pattern runs up and down, rather than left to right). But on a regular head, I'm still confused. If the technical spec of the light source is +/- 11 degress, then even if you could detect a signal on a wide axis, I would think you couldn't jam it.

As a rough analogy, say you and a friend each have flashlights (narrow angle beams analogous to a laser diode or lidar gun). Your eyes are the sensors. Now suppose your friend stands directly to the left of you about 5 feet away. When he flashes his light, you will perceive the light...but you can't get your flashlight beam to hit him directly (ie you can't jam the signal).

Perhaps you guys are modifying the diode in your standard sensors so it has a greater vertical dispersion than the osram spec?

Originally Posted by fire65
The bottom line is, they won't work like that. Go to a testing some time. You will see.
Fair point fire65...just trying to understand why this is the case. Seems like if it weren't, it would open up alot of possibilities for installs.

Have only seen different jammers tested in the same position on the same car (GOL '08 and '07) or the same jammer on different cars tested (various local meets). Anyway, if there is a willing local in SoCal, I would be interested in testing the LI system with the flush vs. stealth setback if I can figure out how to mod the setback w/o tearing everything apart.

9. ## Re: Mounting jammer sensors flush or setback - how much of a difference does it make?

The total beam divergence for the Osram SPL PL90_3 that the LI (and probably other diode jammers) uses is 11 (+/- 5.5) degrees vertical and 25 (+/- 12.5) degrees horizontal. At those angle, power output is half the peak. At twice that angle, the output is virtually zero:

Therefore, if your jammer heads (or input and output diode locations) have +/- 11 degrees clearance vertically, and +/- 25 horizontally, there is no point in wanting extra clearance.
FWIW, Escort's ZR4 jammers have an even narrower field: +/- 2-1/2 degrees.

10. ## Re: Mounting jammer sensors flush or setback - how much of a difference does it make?

Originally Posted by TuonoR

This makes intuitive sense for your HP sensors, definitely (where there is a second diode mounted so the wide dispersion pattern runs up and down, rather than left to right). But on a regular head, I'm still confused. If the technical spec of the light source is +/- 11 degress, then even if you could detect a signal on a wide axis, I would think you couldn't jam it.
The 11 degrees is a measurement made as part of the spec analysis and at a set distance and into either a 7mm or 11mm aperture. Obviously, light physics would allow the beam to NOT stay at a fixed and finite 11 degrees out towards Infiniti for sake of argument.

Cliff

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