Police radar and vehicle vibrations?

Something that I have pondered is it possible to confuse speed radar with a severe vibration of the car? Perhaps intentional caused on the extreme end? Maybe the nose of the car set on an oscillating device, perhaps ultrasonic movements of the panels? Perhaps both and more.

I also though of a rotating drum in front that would have panels moving backward in on orientation and forward in another one with less radar cross-sectional area, and perhaps that could even make it more aerodynamic.

No. Any vibration large enough to confuse speed radar would be strong enough to destroy the entire car.

Not to mention being impossible to drive as well.

People used to put balls of wadded up aluminum foil in their hubcaps as anti-radar devices.

Back to the OP’s question. I do think it would be possible but not practical. Back in the day Car and Driver managed to make a Corvette nearly invisible to radar. The Vette’s body was fairly sharp and they covered those with carbon panels. This left the radiator which they could not cover, but the Vette’s radiator slanted forward and tended to bounce radar signals into the ground. It worked well.

So we could cover most of the front with radar absorbing panels and install the rotating drum made of flaps with a horizontal axis. Time the drum to subtract whatever speed you want from the cars’ speed. Only the rearward moving blades at the top would be exposed.

The actual effect would be that the police radar would detect a range of velocities, a narrow bell-shaped curve rather than a sharp spike. Which isn’t a problem: You just take the peak of the bell curve as “the velocity”, and at worst your measurement is slightly off. There’s always some experimental error, and as long as you know it’s small enough, you don’t worry about it.

I would love to see a link to that.

The OP’s idea might work against a laser speed gun if it affected common targets like the license plate.

I base this on if my hand even twitches a little while using a laser unit I’ll get an error icon rather than a speed reading. The red dot sight has to be on the target steady for about a quarter second. A vibrating plate may skew that. After an error message is received the operator usually tries again on the same target. By the time you realize that target isn’t working and you need to try for another area the vehicle has passed. You can clock from behind, though. So both plates/ bumpers would have to vibrate.

The way to jam radar is to get ahold of a linear amplifier, like from a HAM radio. Have it constantly on. This will trigger the RFI module of the radar, preventing any readings. Depending on the watts of the amplifier the range to do this will be longer than the range the radar can detect your speed.

This could be illegal on several levels, so don’t do it.

I don’t know if the old articles are online. This would have been around 1970 I think. They also did a cab forward semi truck with the slab front.

I remember reading this - it was in the magazine in the late 70’s.

They asked the air force what they used to radar-proof missiles, and bought a couple of sheets. Apparently it was quarter-wave foam with embedded metal particles. i.e. the foam thickness was approximately one quarter the wavelength used by typical radar units. (18 to 40GHz, so 1cm wavelength give or take.). Radar makes the most use of flat forward-facing metal objects - which is why police love front license plates. It bounces off these back to the reader, and the doppler shift indicates the velocity of the vehicle. The idea with stealth foam is that the particles in the foam reflect back the radar wavefront, but it reflects from different points at the same time over half a wavelength, so all the reflections cancel each other out.

(I.e. let’s say the wavelength is 1cm. We have 0.25cm and the signal can reflect from many random points within that thickness - so some of the signal travels 0.5 cm more than others, distance into and back from reflection points. The two signals cancel each other out.

I vaguely recall they used a small Porsche, since it had the sloped front that already made it less detectable. The constructed a rough bra of the material - of course, there are other bits of the car front that weren’t covered. The goal was to allow the driver time to recognize the police and slow to an acceptable speed before the radar picked them up from all the rest of the car, by covering the front end as much as possible. this worked. They got it so the radar would not detect the car until it was about 100 to 200 feet from the radar gun.

The article ended with a caution - while they were testing this on a back country road, while the car was about 200 feet away, a big flat-fronted 70’s Cadillac-type vehicle comes around the bend a quarter mile away and instantly registers on the radar. In this scenario, the police would have pulled over the Porsche and attributed the Caddy’s speed to it.

As for the question - I’ve wondered too, perhaps you could rig a reflective antenna behind the car’s grill, attach it to a high speed vibration mechanism, so it reflects an oscillating signal back. The question is - how does police radar work? Does it average out the signal, or does it try to lock onto a single, steady speed signal (so lack of a steady signal confuses it), or does it average? Also note newer units can detect (lock onto?) multiple return signatures (i.e. two or more vehicles) and show the speed and relative signal strength of each.

Also note some police use “instant-on” so the signal won’t be detected until it’s pretty much taken a reading in a matter of a second or so. Other units use infrared laser - another reason why cops love front license plates, they are usually painted with that highly reflective safety paint, so are perfect reflectors for IR speed guns. Also why some radar/IR guns need aim. At typical detector distances - a few hundred feet - the IR beam only spreads about a yard wide.

Radio Electronics magazine about 1986 or so published plans for a “radar gun calibrator” - point it at your typical radar unit and it would send a signal modulated with the IF frequency and a fixed reading of 30 or 60mph (switch selectable). Of course, this was only so you could ensure your sports radar was reading pitching speeds correctly. The electronics can get hot, so couldn’t be run continuously. To ensure it didn’t burn out, rig it to a radar detector to only trigger when it detected an incoming radar beam.

Police now have radar–detector-detectors, which detect illicit microwave units in cars by looking for the leaking IF frequency. Almost all commercial microwave radio devices use the same IF frequency (100Mhz?) which is why the radar calibrator trick worked. It broadcast a signal modulated with that frequency.

Many (most?) of the speed guns used currently are not actual ‘radar’ devices, but actually use infrared or laser light to do the detection.
And locally, they have a variety of locations where they have carefully measured the distance between 2 visible marked spots, and can clock the time taken to travel that, either from a plane or a nearby police vehicle. Based on the stopwatch time, your speed is easily calculated, and they can issue a ticket.
A vibrating car wouldn’t effect this.

Yeah, this. Depending on the resolution of your FFT you’ll get smaller spikes offset from the main return, but the idea is basically the same. Even the propellers on a prop plane don’t overwhelm the main return from the plane’s fuselage. It’s pretty easy for radar to pick out the main signal and ignore any vibration noise or noise from silly spinny things and such. There have been a lot of gimmicks advertised over the years. None of them work.

Back when I used to work on airborne radar (several decades ago), one of the guys in our office bought a new fancy Toyota, and wanted to turn it into a “stealth Toyota”. Being a bunch of young engineers, we spent about an hour designing exactly that. One of our changes was to tilt the radiator. We were going to tilt it backwards instead of forwards, but either way works. Instead of bouncing the signals into the ground we were going to reflect them up towards the sky.

We had a lot of fun with it, but in the end the changes were far too expensive and impractical (which we expected going into it). We thought we had a fairly decent design though.

By the way, for those that hate TLAs (three letter acronyms), FFT = Fast Fourier Transform. It’s how radar receivers quickly convert incoming radio signals into frequencies for analysis.

Wikipedia page for those few of you who want the gory details:

What creates a bounce of microwave signals, and the primary directional result of the reflection, is an involved science. But, the simplest rule of thumb is metal flat face on to the transmitter works best.

I would expect that propellers don’t produce a confusing signal because (a) aircraft radar is more concerned with detecting a reflection than determining velocity, (b) the body of the aircraft is far more reflective than the propeller so produces the majority of the signal.

I do recall reading in a Homebuilt Aircraft magazine about someone smuggling drugs from the Bahamas to Florida in a Rutan-designed plane. Since these are made of fibreglas the aircraft was virtually undetectable. (Recommended is a conductive paint that will reflect radar waves to help with air traffic control radar). However, the fancier radar resources used by the DEA could detect the aircraft eventually due to the metal engine.

As I mentioned, the IR speed guns are typically the handheld ones since they need to be aimed precisely to get a reading. If there’s a gizmo sitting by the roadside or on the dash not being aimed, odds are it’s microwave radar. I doubt police radars do FFT, because most vehicles don’t produce a variable spread of response frequencies. It just finds the loudest steady frequency and locks on to that. No steady frequency confuses the system - you hope… The vehicle is going X mph which produces a doppler shift between the source and response signals of F. It’s pretty simple. The electronics count the period of that frequency.

Measuring distance between points with a stopwatch is pretty lame. For aircraft - a plane costs a lot to keep in the air - they better produce a LOT of revenue, or really need to reduce hazardous speeding, to justify that expense. Using a stopwatch is problematic. 60mph is 88 feet/sec. So a 5 second interval is 440 feet long. Can someone sitting in a sedan tell when a vehicle is exactly level with a landmark 500 feet away, and then press a stopwatch within a fraction of a second? an again at the other end? If you are off by 1/2 a second each end, that’s a 20% error - someone doing 60mph could be alleged to be doing 72mph. That’s not much better than the good old days when the beef southern sheriff would testify “in mah professhunal estimatshun, the perp was doin’ 10 over the speed limit, yuh honuh.” Radar removes the guesswork.

Most red light cameras are triggered by two coils buried in the pavement at the entry to the intersection. If a car is detected going over those coils in sequence, the computer can determine speed (for a speeding ticket) and whether the car is going too fast to stop before entering the intersection if the light is red. Not much you can do about that speeding ticket except hope there’s a second car in the photo so the offense is ambiguous. Some people have those dark covers over their license - besides being illegal, I suspect they don’t always work.

Yes, but I guess they have fixed that, because I haven’t heard of any problems for years.

One of the academics in the engineering department had a European car with an early electric radiator fan, mounted in front of the radiator, with steel blades. It registered on police radar as the fan speed.

Making your car appear to be going much faster than its road speed isn’t a good way to confuse police radar, but arguably making a car appear to be going much slower than its road speed isn’t good either.

In the UK it was common for a while to see trucks with a row of CDs along the bottom of the windscreen. It was supposed to confuse speed cameras but practical experience eventually showed that it didn’t work.

Over here, licence plates are strictly controlled: size colour (backing and characters), character size and spacing, orientation and positioning. They can only be made up at specific places and you have to prove your identity and that you own the vehicle.

License plates are strictly controlled here, too. They’re made by the government (or possibly a company contracted by the government), and you go to a government office to get them (the trope is that they’re made by prison labor, but I don’t know if that’s true any more, or if it ever was). The products under discussion here aren’t the plates themselves, but a clear plastic cover that goes over the plates. Ostensibly, they’re to protect the plate from mud and rust and such, but the real reason is they make the plate harder to read, especially from an angle (such as you’d get from a red-light camera mounted up on a pole).

If ‘here’ = in the US then I would have to say that it while there may or may not be similar laws on the books, it is much less enforced or followed in the US. It is common to see obstructions such as those covers, license plate ‘bumpers’* which block parts of the plate from an angle, and rear mounted bike racks and various other such attachments onto the rear of a vehicle that make the plate impossible to read.

  • Products like this that even show the plate viewed and partly blocked at a angle (though still readable, bu with further angle it would not be). Amazon.com

The plates themselves are strictly controlled. Other hardware in the vicinity of the plates, not so much. I think most states have laws against those plastic covers, but they’re not enforced much.

Police can issue tickets for unreadable license plates, depending on the situation and their mood. I have heard of tickets for trailer-hitch mount bike racks, sometimes for the trailer hitch ball if it projects up into the way and obstructs a clear view of the plate. (Many years ago, when plates were replaced each year, I recall a news article about some guy in Toronto who got a ticket because his new license plate was printed upside down. The large numbers were the wrong way up, so when he put it on the word “Ontario” was upside down on the bottom of the plate. Some police have no sense of humor or sense of proportion.)

Every so often you will see excessively dark plate coverings. I assume they are a ticket waiting to happen. The one thing I saw which was interesting - a strobe flash mounted over the plate. Most photo radar cameras include a flash to ensure the license plate is properly illuminated in the picture (and the plate has highly reflective paint to help). The idea was to have a strobe slave sensor that the flash would trigger - while the shutter is still open on the red light camera, the flash would light up the plate excessively bright and make the plate picture unreadable.

I was stopped by an older/younger pair of police officers, doing the training exercise. Not a ticket as such, but I was out around $50 USD for the replacement plate. I wasn’t broke at the time, but it still looked like a lot of money. The government had supplied some plates that faded, but mine wasn’t even particularly bad - it was still legible and better than plenty of other similar plates on the road. I was just in the wrong place at the wrong time.