How Police Radar Guns Work
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- Опубликовано: 6 янв 2016
- Explanation of how police radar guns measure and calculate the speed of a moving vehicle using the doppler effect.
Correction: I forgot to divide by 2 in the speed equation towards the end. I just forgot to write that part of the equation on the board. Sorry about that!
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The Doppler effect only works because the VELOCITY of the Sound/Signal is CONSTANT. So if the sender moves toward the receiver, the only way to fit the same number of oscillations in between is to compress them. And compressing waves means increase the frequency.
(This is how my Physics Professor explained it to me, 20 years ago ;-)
Cool
Nice
You are killing it on the new videos. Great to see your channel evolve like this.
+JDH Thank you! :)
this was perfect! just what i was looking for :) thank you!
Great Explanation. You made it so simple. Thanks man
Great explanation! Very well done!
Perfect, well done! thanks a a lot. This is the best you tube video in my opinion
Awesome explanation, high quality. Thank you!
Excellent explanation!! Thanks
This was a very well made video and explains the science very well
Killer video, keep it up!
such a great explanation, nice video man
I really like your new style of videos of you showing your face and teaching. I feel like you are a very knowledgable professor teaching the class an important lecture! haha. nice work!
lol
@@VortexRadar Hi Professor Vortex, can the Uniden R3 work in Malaysia?
Jesus man thanks a lot. I have a project in school for the Radar Gun and this explains things so much better than any article. Amazing content man
Nice video dud, really help me with my study
Thanks dear I appreciate this video as I lent the theory ( equation) behind this.
No
thank you for your good explanation
Great explanation!
beautifully explained my dude. A1 video. thanks
ryker bowen says....I feel like you are a very knowledgable professor teaching the class an important lecture!
now is that a compliment or wat?? lol
anyways nice job vortex!
The original frequency is same all times ?
Excellent tutorial
Your videos are awesome and you are really nice to look at. :)
Subtract 1 from both sides in Doppler effect formula {fr = fo(v-vo/v-vs) vo is velocity of object, vs is velocity of source, v is velocity of sound, (sign convention = positive when moving in the direction of sound otherwise negative)} to get the formula written on board.
Thanks, man. I was struggling (because I'm a layman) to understand the interaction between the two.
So, when does a radar gun actually have you when using the R3 ? When the R3 starts to alert, at full "beeping", or when ?
But how is frequency measured? Especially these high frequencies. We can't just measure the peaks and count them so does this use some sort of a resonance circuit or what exactly goes on?
Will other vehicles between me and the police officer interfere with radar? I was stopped about a month ago and the police officer was approximately 1/2 Mile to 1/4 Mile in front of me. There were two other cars between he and I just as his lights went on
Great info. You rock!
Could it be used to monitor and give feedback on the speed of a moving swimmer?
Is it possible to generate some signal un orther to block the radar?
Do you have to be direct in front or behind for this to work
Amazing! Thank u
How to you calculate the reflecting frequency? Thanks
thank you for the simple explanation. :-)
What if the car change it’s speed
@@xmenxman686 it will dance!!!🤣🤣🤣🤣
@@xmenxman686 The raider gun will show a new speed
In case of mounted radars (on a car for example) the change in frequency due to movement of target vehicle; will the reflected waves be more compressed due to the movement of radar device also, will there be more change in frequency, in that case will the velocity displayed be accurate?
I believe the radar guns compensate for movement of the police vehicle or takes it into account.
Man I love your videos! So educational. I recently purchased a redline and programmed it to your specifications with your tips. I'm located in Missouri and had to turn off my K band because it never stops going off. Should I keep it on and just turn on TSR or does that "cripple" the K band too much so I might as well just keep it off. Thanks in advance for the help.
Oh yeah, TSR is basically a must in most places. You do lose some range and it becomes a little slower, but without TSR the detector can be pretty unusable in populated areas so it's a necessary trade-off. Try out Auto Mode as well to help with the falsing further. Then add lockouts using an Escort Live cable and you'll get some more filtering in the city too. :)
+Vortex Radar thank you. One last question. If I am running my RD in spec mode and k band goes off is there a frequency that when I see it I should know "oh that is most likely a cop and not a blind spot false alert"?
+Barry Sanders on K band, not really unfortunately
2:09 - Question: So are handheld radar detectors more difficult to avoid with a detector since they actually have press the trigger when targeting a vehicle, thereby preventing a detector from receiving the signal?
Dashmounts also have a button to start and stop transmitting
Hey idk if this question was asked before but if you’re moving in a pack of cars going in a straight line at variable speeds would this change out come of the radar gun reflected signal or would you have to recalibrate the gun every time?
No need for calibration. Wouldn't be practical
Might be a stupid question but would the radar read 0mph if your pointing it perpendicular to the the motion of the vehicle ?
You are the man when it comes to all things radar/radar detectors! Keep it up.
I know I’m kinda late but how do they adjust for angle? Is this why they subtract some amount from the measurement? Or can you just measure the cars when they drive straight at you?
Alright so it is important to measure straight on otherwise it results in inaccuracy due to cosine error. But the measured speed would be slower than the actual speed which works in your favor (at least if your not the police man).
For handheld radar it’s essentially impossible to account for cosine error but I think if a stationary radar always measures the car at the same point on the road they could factor in the angle. Nonetheless the difference is minor and would only please the driver.
thanks for explanation
Liked and subbed. Great explanation. Great video.
Welcome aboard!
Hey! this actually helped. Thanks man!
Very helpful.
thank you so much
Great explanation, just wanted to say that the graphic at 0:45 is a little confusing. To me, that looks like a car slowing down and so the soundwaves are the wrong way around.
I love your drawing of the car
well explained.weldone
do the radar unit has a volum setting or makes click sound? how do it al
Haha yep, it does
So how did you come up with the 6713 number? I understand how you got the difference of the transmission and the reception. But I’m unclear where the 6713 came from. Thanks in advance!
That’s the example # he used as the frequency returning back to the radar gun. Basically the difference between the 34.7 GHz and what was reflected back from the target vehicle.
wait so are u suppose to divide the final speed you got by two? im not clear on when the division by two was suppose to occur.
+Mahdee please see the video description :)
What happens if the target is moving perpendicular to the direction the gun is facing? Will it just read 0? And if so, will there have to be extra calculations taking into account the angle the gun makes with the direction the target is moving?
Yep, 0. Google cosine error.
If I have a radar gun or device at a car that transmit exactly same initial freq at higher strength. Would it jam the other radar gun?
No. Radar guns are designed to track multiple vehicles moving in different directions, some bigger and some smaller, some faster and some slower. They have strongest and fastest modes so even a strong signal won't prevent a faster signal from showing up on screen. Normally the classic example is a big slow semi and a small fast sports car. The sports car is faster (weaker signal) but the radar gun can still capture its speed in addition to the stronger return signal of the semi. Jamming and returning a fake signal are two different things. :)
Does the radar need to be directly behind or in front of the moving object to determine an accurate speed? Or could you radar something from its sides
Good question. Radar is subject to the cosine effect copradar.com/chapts/chapt2/ch2d1.html so it does have to be pretty straight on. A side reading wouldn't work.
Vortex Radar thank you!
Isn't pitch the frequency of sound waves, not radio waves? Thank you for the clarification in advance.
Yep! It’s an analogy. ;)
Not too sure if you mention about the sound of different cars. My car is louder than the usual. Does that mean if 2 cars are traveling, the car with the louder engine sound will be detected? Am referring to station radar detector on the street side.
No, that doesn’t have anything to do with it
Why do they use this equation, i mean is there any explanation why divided by original freqeuency?
Hi. Great explanation. Can I ask: Do radar guns work through the windshield of a car?
Yep
They will also go through fibreglass, but it weakens the signal. Which is why fibreglass cars can be harder to detect. The signal goes through, bounces off the metal parts underneath and then has to go back through. It's why fibreglass hulled boats have radar reflectors on the masts.
Excellent explanation my friend. My question is what if you are moving and the police is also moving, is it possible to get an accurate speed?
Yep! Here’s how that works: ruclips.net/video/FL7yhwK158A/видео.html
But what about if the radar gun is at a 90 degree. It'll be zero right? So the radar gun has to be parallel or smaller angle than 90 to detect a moving object yes?
Correct
Does it have an effect if the radar gun is also in motion? One time I passed a cop (we were going opposite ways on a 2 lane road) and he flipped a U and got behind me and pulled me over and gave me a ticket for speeding when I knew I wasn't speeding anywhere near the amount he said I was cause i had cruise control on. Was this just a lying cop or would *both vehicles doing roughly 50 mph towards each other* effect the result the gun shows?
Radar guns are designed to work when moving too. ruclips.net/video/FL7yhwK158A/видео.html
thanks, I recently dived into radar and got so many questions to ask. Please help if you could get some of that answered. 1) There is an accuracy for each radar device. Will that changing over various distances? 2) How can Doppler frequency be calculated?
2)What do you mean with that?I think all he did is input 65mph to the equation and found the fr(reflected frequency) that way.You dont really need to know the doppler frequency all you need to know is the change of that frequency.
Good content
Hello, what if another car crosses in between the radar gun and my car, will it give an inaccurate reading ?
+Carlos Gomez Nope, it’ll simply show the other car’s speed.
you are a good men
Fist of all, your videos are very informative, to the point and well detailed! Keep it up!!! I also have three quick questions, I'd really appreciate it if you could answer them!
1)What is the range of most radar guns in order to clock your speed accurately, in order for someone (me) to get a ticket?
2)Also can the police with a LASER gun clock you while the police vehicle is being driven? ( I know its possible while using radar gun, but not sure about laser)
3)I have the escort redline, is there some sort of a method to understand if the signal is coming from the front or the rear of my vehicle? (the redline doesn't have any arrows as you know, so are there any elimination steps that I can take in order to have some kind of an idea)
Thank you for taking the time to answer these burning questions I have loll! Keep up the good work :D
+4shebby I'll do a video on your first question since it gets asked so often. The answer is that it depends wildly.
The second one, laser is stationary only. I'll do a video on moving mode radar and it'll make sense why it doesn't work with laser.
You can sorta tell direction with an arrow-less RD. You basically just pay attention to the signal strength on the display and the audio rampup and correlate that to what's going on around you in your terrain. It takes more brainpower and analysis, but it's possible.
ok awesome for the quick reply! and as for the third pard question, im guessing if theres a cop behind or in front of you and they turn on their gun, the signal is going to be super strong. Also how long does the radar gun needs in order to give you an accurate reading which the police can ticket you. Once there was a cop behind me and he kept turning his k bank gun on and off20-25 seconds each time. How long do they need to clock you before they are confident that you are speeding or not (5-10 seconds?) thanks
Not a simple answer. It might be best to ask on RDF so you can get answers from a bunch of people and so others can benefit from the discussion too. ;)
i shall try and do that. Thank you :)
Great video
Does wind play role in radar detecting faster speed of vehicle?
No
Nice Engineering Explained RUclips channel Style.
thanks
Those the radar need to be stables or could be in a movement ?
ruclips.net/video/FL7yhwK158A/видео.html
You can jam that by sending the original signal in another direction and spoof it at the same time by sending/repeating the same signal back frequency adjusted based on your current car speed.
It’s a little more complicated than that (and highly illegal), but yeah that’s the idea.
LOL 😂
is it true some radars has dual antennas and could clock the speed of 2 different vehicles?
Yeah some can clock multiple cars like the strongest signal and the fastest signal both.
What will happen if I have two radar sensors, and their views are overlapping?
i dont understand how do they measure the speed of tennis balls or baseballs since they are not metalic materials? can those materials reflect radio waves?
+tirips etihw Solid objects reflect radio waves, correct
Can it read two car speed at the same time
Does the distance between the cop using the radar and the road he used the radar gun on, change the accuracy? Does a cop using radar on a road that has a bend change the accuracy?
Distance doesn’t affect accuracy. Angle can somewhat due to cosine error, but that’s always in the driver’s favor.
Learned a lot from this video thanks! Do cops really use aircraft to monitor daily traffic and speeders? If so would a radar detector pick it up? Cause I read just uses time and how fast the plane/helicopter is going to measure your speed.
They do in some places, yeah. A radar detector won't help.
Do Radar guns take photos? Uk
if radar gun is also on moving opposite vehicle will that speed be accurate because if car towards coming to radar gun will be doubled i guess
Yes. They can do moving mode just fine. Opposite lane monitoring is easier for radar guns than same lane monitoring.
Can anyone tell me how they shoot me behind them going the same direction how accuracy
Thnx alot love from delhi (india)😇
how are you suppose to find out that the change in frequency is 34700006713hz if you don't know the speed the car it travels (i mean the radar gun will show; but is there way to calculate the change in frequency by the speed of the car?)
+Justin C The radar gun does that all itself under the hood. That change in frequency is what it uses to determine the target speed.
btw how is speed of light 6.71x10^8 ?? isnt it 3x10^8 ?
Since we want to measure vehicle speed in miles per hour, what happens when you convert meters per second to miles per hour? ;)
Vortex Radar ohhhh damn i missed that, thanks
I have a question: if a radar gun is pointed not directly in front or
Behind but to the side of a vehicle willl the reading be false?
That won’t work. Google cosine error.
@@VortexRadar thanks so much for the responses I’ll look that up
Who else did the math the exact same way he explain and got ~130 mph?
He forgot to add the fact that you divide the final answer by 2 because the radar gun originally calculates the distance both ways so it doubles the speed. Halving the result will give you the actual speed of the object. So, in this case, 130 mph divided by 2 is 65 mph.
what if your both driving towards each other at 50mps is it still accurate
Yep, that's known as moving mode radar. Here's a little info about it: ruclips.net/video/FL7yhwK158A/видео.html
What will happen if you point two guns against each other
I am thinking about tiggering a gun whenever i receive a signal in the radar detector
The two guns won't interact in any way whatsoever. I take it you're wanting to jam the other radar gun? It doesn't work.
Tnx a lot
Hi... video is very useful. What if the policemen moved his hand while he is activating the device? Can device give a wrong result?
Why would it?
@@VortexRadar when the policeman holding the speed camera, there is a possibility of shaking his hand. Will that effect to the results?
Again, why would it? These are designed to be used handheld by humans, not just on a tripod, so some handshake is normal.
Point at target and pull the trigger. Simple. Don’t shake it like maracas 😄, but handholding is otherwise fine.
@@VortexRadar true. My question was, if there is a hand movement, the results shows in the device can be wrong. Yes or No?
What's its accuracy
Very odd question, is there any reason this wouldn’t work as well if we were to point the radar gun at a swimming marine animal that’s breaking the ocean surface?
I like this
I was told by a radar cop that the radar must be a straight line, not facing up or down facing the car? Can that give a false number?
Yep, Google cosine error
What if you put the car into neutral before the speed gun hits the car? What happens then? Does it still calculate your speed ?
Of course. Your car is still reflecting the signal just the same, no matter what your transmission is doing.
Ottaney Bell Well obviously, you’re still moving. You would have to slam on your brakes & probably cause an accident lol.
Thanks. So in essence there isn't an actual way to beat the speed gun at recording your speed then
Ottaney Bell There actually is. You can buy a radar that will notify you if anyone is pointing a speed gun at your car, giving you a chance to slow down.
I always wondered how wide do waves get, or do they stay together like a cylindrical shape? I doubt it, but hopefully the expert Vortex knows this or anyone else. I can't seem to find that on Google, so thank you in advance.
In general it's a cone with a ~12 degree beam width, but radar does spread/bounce around far more than a laser does which is why we can pick it up around bends and over hills.
if you watch an aircraft at cpa then time the seconds until the sound of it gets to the very same place you can guess its distance from you.
its back to school for me cause you totally screwed me up
Thanks, but this only works for a zero angle between the direction of travel of the car and the direction aiming the gun. Which is never the case unless the officer is standing in the middle of the road. OK so if you know the angle you can still calculate it, but how does it work for an unknown angle? For example when you're trying to measure the speed of an RC plane flying over your head.
+Elias Labordus Cosine error isn’t a huge factor unless the officer is at a sharp angle. Run the numbers and you’ll see.
That is why there is a theshold for error for example some countries state that for ex speed limit is 100km/h you will get a ticket if you were driving at least 10 km over speed so for example you were driving at 107 and for any reason the radar registered a 110 (3 km error) you already over 100 but some time you get 109 then no ticket!
I think it should be ∆f/f = 2v/c
Hi, there is a factor 2 missing in the formula (see en.wikipedia.org/wiki/Radar_speed_gun)
Speed = Δf/f0*c (=129,8…mph) should be Speed = 1/2*Δf/f0*c (=64,9…mph)
Yes I did why is why I put correction notes at the top of the video description, hoping people would see it. Sorry about the mistake when preparing the video.