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Now you "see" me...


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A few weeks ago I rode a stretch of highway with numerous "Your Speed" radar advisory boards posted along the side of the roadway. I was on one of our department's older RTPs (2003 R1150RTP) and found that the boards didn't register the speed of the bike until I was about 200 feet out, but it did register. Rode the same stretch of road last week on my 2006 R1200RTP and found that all except for one board completely failed to give a speed reading. So, I get to thinking about the angular front end on the 1200s and started wondering, "Stealth bike?"


From my experience with handheld RADAR/LIDAR units, I know that it is more difficult to get a reading on a motorcycle than a car. The frontal area is just so small in comparison. However, I was surprised about the boards, because they are typically outfitted with a radar that offers greater sensitivity, but lesser accuracy.


Just curious if anyone else has had similar experiences with roadside radar boards on the R1200RT(P)...

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Funny you should mention. Highway 12 from Fairfield to Rio Vista has a whole big line of speed boards. They seem to register fine for cars and trucks, but they don't seem to see me (2008 RT) and they WIG OUT when they do.


Oddly, I get consistent readings on the gsxr, and it has a much smaller frontal area.

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Frontal area is only one of many factors at play here. You get the largest reflections from the intersection of three mutually perpendicular planes – look at small boats, they often have a lozenge-shaped radar reflector on the mast.

For a metallic surface, the lowest reflections come from a structure that has total internal reflections.

In fact, reflections is not an entirely accurate description of what a radar return is. They are a re-radiation of the signal from the edges of a conductive material. The Radar signal induces surface currents in the target which propagate through the material until it comes to an edge or break in the surface, at which point it is re-radiated in a direction dependant upon the shape of the edge.

On something like an RT, the Tupperware can also influence the return signal. Depending on the characteristics of the material (including paint finish) the plastic is translucent to RF, but it will attenuate the signal a bit. The reduces the strength of the signal reaching the underlying metal and also the reflections emanating from them. It is theoretically possible for metallic paint to form a conductive layer, bleeding the signal toward the rear of the fairing and causing it to re-radiate away from the illuminating radar.

A stealth RT? Certainly possible and with a little more effort (conductive coatings, closure of reflective shapes etc) they could be very difficult to detect by radar from the front. Illuminate the machine from the rear however and all bets are off.




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My experience with roadside boards indicate they only register up to 99 MPH. ;)


Thanks, I have often wondered if they could manage triple digits.........

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Actually, I find that they light up for the car behind me, more often than not.......If there are no other vehicles, they don't seem to detect my R1150RT until I am on top of them.


By the way, mine is black, and usually dirty, if that has anything to do with it.

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Millimeter wave (K Ka band) radar will reflect off most anything. It likely reflects a bunch off the paint and windshield. But, if the majority of the reflections are angled away from the source of the wave, it won't likely return much signal. It is possible that the tupperware is angled very good for stealth and the windshield hides the reflections of the driver. Although, it shouldn't be a huge difference between another bike with similar tupperware and windshield. A stealth fighter reflects a very tiny amount of radar signal only if the radar was in front of him. It isn't stealth from a radar under/over him or beside him. Donno about the rear.


Imagine if your RT and yourself was coated with silver and every surface was a mirror. What would the reflection of light from a distant flashlight look like from the holder of the flashlight? Radar image isn't exactly the same, but similar. If the radar does penetrate the tupperware a little, the image would then include faint images of stuff behind the tuperware.


Since the radar antenna doesn't scan, it simply detects all this returned waves and detects the peaks of all this. So, it is like a light meter. Once a peak is found, it determines the shift in wavelength or frequency which is proportional to your speed. The doppler radar also must reject the biggest reflections which are the ground and nearby objects. These are not moving, so the unit can filter them. But all filters have a finite range of frequencies, so the radar gun is likely useless below a certain speed. You need some speed in order to be detected. BTW, you also can go undetected if you have a bigger moving reflector nearby (like a truck off your side). Just be sure he is moving slower than you !

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