Kinda the opposite of Wonder Woman’s invisible jet plane.
I think it was Radio Electronics about 1986 that had an article on making a “radar gun calibrator” ;| so it could send a signal that your radar gun would register as 55mph (or 35mph, depending on switch setting). Basically no matter what microwave frequency the gun used, it used a standard IF frequency (100MHz? seems to ring a bell) for the intermediate stages. So the signal was modulated with the IF frequency that itself was modulated with the beat frequency expected if the reflected signal was doppler shifted to the desired speed. Since the bandpass filter to the first intermediate stage (IANAElectrical Engineer) was filtering ambient signals for the IF frequency, the calibrator signal would sneak into and dominate the IF stage, overriding a much weaker reflected signal.
As a side note, since all microwave devices use (used?) this standard IF stage hardware, this is how radar-detector-detectors work. A friend whose son was in the Ontario Provincial Police described how they’d sit a bit back from a crossroads with the rural highway and wait for the detector signal to go off, then chase whatever vehicle went by when the signal went off. Apparently all microwave devices leak that signal - at least, until manufacturers figured that out and the higher end ones allegedly don’t.
I recall the (an?) article in Car and Driver about 1980(?) where they called up the US Air Force and asked what they used for radar stealth. They were told about a foam that could absorb radar. It was a foam about a half-wavelength thick, embedded with flecks of reflective material. the idea was that a wave instead of reflecting off a surface, would reflect off multiple levels over a half-wave (quarter-wave?) in the foam in such a way that the sum of combined reflections would cancel each other out. IIRC they used a Porsche (since it had a sloping hood and low profile). They built a bra covering much of the front end. The net result was a car that could not be detected until it was about 200 feet away; the theory being not that you could blast past the cops, but that you had plenty of time to spot them and slow down.
And yes, while testing it on a country road, they instead picked up a large flat-fronted Detroit lead sled (Cadillac or similar?) coming around the corner a quarter-mile away… pointing out one of the hazards of stealth mode.
They mentioned the same effect could be had with paint, but it would have to be relatively thick paint. 10GHz signals have a 3cm (little over 1 inch) wavelength, so a 1/4 wave shield would be 7.5mm, a third of an inch.
Police also use infrared laser signals to catch speeders. When you see them aiming like they were drawing a bead on someone, unless the driver is black, odds are they are aiming an IR gun for the license plate which is highly reflective for this purpose - explaining why so many states are hot to trot about having revenue-generating front license plates. By aiming, they can be sure which vehicle they are targeting more precisely than with radar - I have seen articles that state the aim is within 3 or 4 feet diameter, so hard to mistake which vehicle is being tracked.
I have seen assorted suggested tricks for defeating this. A 90-degree reflector on the moon was able to bound a laser signal back to earth, three-corner 90-degree reflectors are very efficient, just like the highly reflective paint on licenses. Someone suggested mounting the license on a vibrator, so there was no steady reflected velocity; another was to mount 3-corner reflectors on a vibrating base again, so there is no fixed speed; However, I have yet to see anything like this works, since what the device will likely do is average the result - giving your actual speed. A license plate cover IR filter is probably the most effective - but then again, only to a certain range.
IIRC the opening paragraph to the article was that when the radar detectors in their Corvettes go off they hit the brakes, but when the detectors in their F4s go off they hit full afterburner.
Another point I heard was that the boom in home-built aircraft made of fibreglass - if it weren’t for the type of paint, they would be almost invisible to radar since the only significant metal was the engine and firewall; apparently something that the DEA and Border Patrol learned. But then, I presume there’s a difference between FAA radar and speed-gun radar in terms of range and detection.
[Moderating]
I assume that you weren’t making a comment about the IR reflectivity of melanin. This is not the place to discuss cops shooting black people. That place is either of at least two threads in the Pit, or possibly a new thread there or in Great Debates. Keep this sort of commentary out of GQ.
A better way of defeating them is to just have a detector. In Texas, with no front plate to hit they just aim for your headlights to get enough reflection. Most cops wielding them have a pretty terrible aim. You can easily drop 20-30 MPH in the time it takes for them to sight you in and get enough of a reflection from your front plate or your headlights from the range they usually shoot (and the act of braking means the target moves). In the years since I got a lidar detector, I’ve gotten one ticket from a lidar gun. That particular cop is Quick-draw McGraw. He popped out from behind a bush at a range of about 50 feet, and nailed me, even with no front plate. That’s technically not a kosher location for them to work traffic from, their vehicle is supposed to be in plain sight from the road when parked on the shoulder for enforcement here (for the safety of all), but I still complimented him on his technique and just paid the ticket.
To be honest, I think a radar gun was more of a revenue maker. I know that even with a detector (the same detector as above), when radar guns were more prevalent I had more close calls from smart, prudent traffic enforcement from those than anyone under the current lidar gun regime. Cops who cruised around with the gun always on or just blasted every third car with radar weren’t any difficulty. They were visible to the detector from a long way away. The guy who was able to tell speed differentials at a distance and was patient enough for you to come in range was more sure of issuing a ticket with a radar gun that read instantly than a lidar gun.
I’ve had two cops recently paint me constantly with lidar from about an eighth of a mile out until I passed them, driving a car with a front plate, without them getting a reading in the last month. How did I know? Because they were still pointing it at me, I had slowed down long ago, and the detector was still going off as I passed. I’ve never had a cop with an instant-on radar gun paint me for more than a few moments. A radar gun has a much better chance of getting a legally enforceable reading, IMHO.
And yes, radar emitters are illegal, but they were once almost practical. I had one in the '80s that I had bought second hand in a thrift store for less than a pack of cigarettes . That place was like the store where Hoyt Axton bought the Mogwai, but piled high with all this amazing looking crap, some if it electronic. The device in question looked like someone had crammed the contents of a grocery store’s door sensor into a powder coated project box with a speaker, a light, a knob and a cigarette lighter adapter. I didn’t really know what it was when I bought it, but I had an inkling. With a friend’s radar detector, we could tell that it blasted the right band. After driving around for a little bit, I also realized it was a really terrible radar detector, as the speaker would sound an alarm and the light would illuminate whenever I approached an underpass or other large object. The knob controlled the volume of the alarm. The fact that you’d have to carry around several emitters would make that device even more impractical now.
I’m a sample size of one, but I drove around with no tickets for a year before I realized “This is as crazy as running from the cops. I’m turning a minor offense into a major one if I get caught.” - which was probably the same thing the original builder realized before it got donated to that shop. The year before and the year after I drove with this thing I got at least 4 speeding tickets. I maintained a similar rate even after getting my first radar detector that wasn’t someone’s loony idea crammed in a project box. It only stopped once I got a much better radar detector and started to pay better attention to the damn thing.
Either way, yeah, even though the detector makes speeding much cheaper where one is legal, it’s even cheaper to mostly obey the speed limit. Nothing will protect you from a cop that paces you, or an airplane that times you between lines on the freeway and radios your plates to a cruiser.
Do police still use aircraft? I remember that was a thing in the 1960’s and 70’s when they had signs posted. But I saw my first radar speed trap (mounted on a tripod) about 1966 and its got to be far more cost effective to use a ground based radar. Plus a small Cessna goes about 100 mph it would have to zigzag to properly watch a stretch of road and be pretty low-flying to read license plates. More likely just identify cars by color and current position to ground troopers.
A friend of mine was driving on the highway with a friend of hers, who was a cop.
They passed a sign that said “Speed monitored by aircraft.”
She grumbled, and said, “I wonder how much that costs the taxpayers?”
He smiled, and said, “Signs don’t cost anything.”
Anti- radar paint,
turbocharged, J.J.
Nobody can stop us now.
Nobody.
Except zombies. -Captain Chaos, more or less
In the late 90s I got ticketed by a trooper who actually apologized and explained that it wasn’t his idea to pull me over, I had been flagged by a plane which contacted him. That must have been in ‘98 since I was transporting movie reels at the time (I worked at a movie theater on a Naval Base).
He apologized because I was going 65 in a 60 and I guess he’d have never pulled me over if it was up to him. That was the first and last time a cop ever apologized to me. (At least while citing me for an infraction, I interact with police I work with all the time now and of course they’re generally polite.) It stuck out both because of the plane and that odd apology.
Assuming he was telling the truth and not just filling his quota - maybe the cost of the aircraft was so high that they HAD to hand out any ticket they could justify.
I assume most judges will toss out a ticket that shows less than 10mph over the speed limit? Although I did see a discussion in New Zealand years ago about how the police or politicians waned to drop the margin on photo radar to 5kmph (3mph) instead of 10kph because - money.
Usually the NZ Police will allow a 10km/h tolerance on the open road (100km/h, or 110km/h on some small sections of Expressway).
During defined holiday periods (Easter, Christmas/New Year, and two long weekends) where traffic density is greater (and the road toll is commensurately higher) the tolerance drops to 4km/h. The primary motivation is safety and reducing the road toll.