Technical radar question

All radar talk seems to be about how "the beam" contacts and object and then it gets returned or reflected off that target back to the antenna and the time it takes for this to happen results in a speed. or something like that.

What if "the beam" gets split in half? In your expert opinions, could a radar beam/signal get messed up when the officer shoots this tractor-trailer combination in the back? It seems possible to me that a signal might be returned to the antenna from the rear of the trailer while another signal might be returned from the rear of the truck

Good question.

But I have no idea

You would need a technical expert in radar to answer that question.

That's why I'm here. They are no doubt thumbing through their training manuals as we speak.

EDIT: I understand that with moving radar, the radar uses stationary objects to compare the target to, but the same question applies. Is it possible that the extra time and distance that the signal must travel from the rear of trailer to rear of truck could throw the radar off?

Radar has the ability to process many returned signals at once, it will only display the strongest returned signal. So, if there are muliple vehicles in a radar beam, the speed displayed will be from the strongest returned signal. In your tractor and trailer combination, the front of your truck will have a much stronger returned signal due to its size, shape and composition. Not only that...the trailer must be going the same speed as the truck anyway.

Radar does emit a rather wide "beam", so it's possible that it would be striking your cab and trailer at the same time. Unlike laser though, radar isn't measuring the time it takes for the signal to be returned. Radar works by emitting a signal at a known frequency. When the signal strikes a moving object, it gets reflected back at a different frequency. This shift in frequency is how your speed is determined. The frequency shift would be the same if the object was at 10 feet or 1,000 feet. So even if the radar was getting a signal return from both your trailer and cab at the same time, the reading would be the same for both.

If your trailer and cab were somehow moving at two different speeds, the radar would get then get two separate readings. The radar would then display a reading for the strongest signal or, if selected by the operator, the fastest speed returned.

" I understand that with moving radar, the radar uses stationary objects to compare the target to"

Not so...In the moving mode, it is the police vehicle that establishes its patrol speed from stationary objects, such as, the ground in front, rock cuts, signs and such. Stationary objects have nothing to do with getting the target speed.

Stanton, ....comes back at a different frequency......I see. That's why the tuning forks were used to check the target acquisition accuracy. Thanks.

EDIT:I can't get my head around how the something as simple as target speed can change the frequency of a radar signal. Gonna have to google how radar works in a little depth.

Screech....Ok so the police car uses the stationary objects but....(just a point of clarification here for me).....must be the radar in the police car sending a separate signal out to pick the stationary objects then....i.e. one signal for the target and another different signal for the stationary targets?

It's just one signal (beam). The easiest way to explain it is: The strongest signal returned is used as the patrol speed of the police vehicle and the second strongest signal is the target.

Inside the radar, the single signal actually gets split to do the calculation of a patrol speed and target speed.

My guy was sitting at a stop sign as I passed in front of him, allegedly at approx 80-85 kph in a 50. His notes say that he turned right, activated same direction and locked my speed at 72 when he was 30-40 meters behind me and his patrol speed was 60 kph.

1. How long does it take to activate same direction? I understand he has to press and hold a button?

2. For him to be telling the truth, he must have peeled away from that stop sign at a pretty good clip. Can rapid acceleration of the car or engine produce high target readings or inaccurate stationary readings?

3. Nowhere in his notes does he mention that he turned the radar on so I assume he was traveling with the radar on before he reached the stop sign. If he had to turn the radar on, how long does that take?

Decatur wrote:

It's just one signal (beam). The easiest way to explain it is: The strongest signal returned is used as the patrol speed of the police vehicle and the second strongest signal is the target.

Inside the radar, the single signal actually gets split to do the calculation of a patrol speed and target speed.

Ok well then I must have been a pretty strong target. How do we know the radar wasn't shadowing?

Here is an interesting side note... how does he know you were doing 80 to 85 when you went by him at the stop sign? At a 90 degree angle (with head facing straight ahead) the radar will read 0.

Is this just officers estimation of your speed as you passed in front of him?

The head of the radar unit must be mounted somewhere on the vehicle for moving radar (hand held radar is not used in moving mode). Was the head moveable, meaning he can turn it 90 degrees to face left/right and then back to straight ahead as he pulls in behind you? I think (not 100% sure) they are usually mounted straight ahead and are not moveable.

rank wrote:

EDIT:I can't get my head around how the something as simple as target speed can change the frequency of a radar signal. Gonna have to google how radar works in a little depth.

Probably one of the best analogies is from the wikipedia page on doppler radar:

Imagine a baseball pitcher throwing one ball every second to a catcher (a frequency of 1 ball per second). Assuming the balls travel at a constant velocity and the pitcher is stationary, the catcher catches one ball every second. However, if the pitcher is jogging towards the catcher, the catcher catches balls more frequently because the balls are less spaced out (the frequency increases). The inverse is true if the pitcher is moving away from the man. He catches balls less frequently because of the pitcher's backward motion (the frequency decreases). If the pitcher moves at an angle, but at the same speed, the frequency variation at which the receiver catches balls is less, as the distance between the two changes more slowly.

From the point of view of the pitcher, the frequency remains constant (whether he's throwing balls or transmitting microwaves). Since with electromagnetic radiation like microwaves frequency is inversely proportional to wavelength, the wavelength of the waves is also affected. Thus, the relative difference in velocity between a source and an observer is what gives rise to the doppler effect.

Jsherk, He said he could tell just by looking because he is that good From the time I crested the hill and came into view to the intersection is ~40 meters. That is less than 2 seconds at 85 kph. Not much of a tracking history.

Anyone would have to be INSANE to enter town at that speed. Pic below is taken from the officer's exact vantage point and I crested the hill coming toward him as he sat at the intersection.

That's an easy skill to learn if you are using radar or lidar regularly and be within +/- 5 km/h ever time.

Decatur wrote:

That's an easy skill to learn if you are using radar or lidar regularly and be within +/- 5 km/h ever time.

He was off by 26 kph.

However I don't think he's that incompetent. He pulled in behind me and realized that he missed his chance because I was already down to ~45-50 from 59. So he just bided his time and got me outside of town. Made sure to wait until I was over 65. I'm sure the tactic has been used before.

Your opinion is he was off by 26 km/h. He would probably say different. That's why we have a court process.

The last thing you want to do if you have another trial would be to admit that you were speeding on the stand.

Rank;

That is Bloomfield isn't it?

Not really sure which one has the opinion, since II had the benefit of thespeedometer. Your point about taking the stand is well taken. Will just have to see how that goes. I remain skeptical about a conviction for 72 being fait acompli because I admit to 59.

If you admit to speeding (even only 59) and the officer says you were going 72 then most likely you will get the 72 charge. If you did not testify at all, you would still get the 72 charge but you saying you were speeding just helps their case.

Best case is the JP drops it to the 59 but I have been to court enough times and never seen them do that. They always go with the officers "radar" speed.

So there is no point getting on the stand and admitting you were speeding at all.

You should just work on the cross-examination to bring reasonable doubt to officers testimony so you have a chance to win.

Remember you are not guilty of anything right now. You are innocent until proven guilty in the court. So make them work for it.

Sometimes I find it helps to use an extreme example to make a point.

Let's say the officer charged me with 1,228 km/hr in a 50 zone. I plead not guilty to 1,228 and I put myself on the stand and testify that I was only traveling 80 in a 50. I know this to be a 100% true statement beyond a reasonable doubt because the officer testified under cross that he did not hear a sonic boom. Will the judge still find me guilty of 1228 in a 50?

My point being, in my view, the physical evidence in my case trumps officer testimony of when he pressed his radar button.

As decatur says, that is why we have courts. We shall see. If I am granted a new trial that is.

Well you are welcome to try and I hope you succeed.

I will be surprised if you succeed, but I still hope you can do it.

I've heard it said about other trials, that a defendant can't win if he doesn't take the stand. I think the logic is that the judge/jury need to hear that you didn't do it. If you can't take the stand in your own defense it doesn't look good I suppose. Not sure what's different about traffic court.

I'm more concerned about navigating the procedural minefield than I am about what happens during questioning.

Again, I appreciate your advice and we'll see. All the best laid plans are often for naught when a surprise happens. A lawyer I respect told me once that you can never tell what will happen at trial. There is always a surprise. I think he was worried about me folding under cross but the surprise that day was it was the officer that folded LOL. There is no place to hide on that stand. There are liars and cheats everywhere among us but the laws of physics have no prejudice, no career goals, no axe to grind, no quota, no ego.

BTW, The Stig, I replied to you by PM. Not sure if it went through or not. Still learning this message board format.

The difference is that we are talking about an ABSOLUTE LIABILITY speeding offence... there is no acceptable reasons why you did it (unless your life was in danger). Either yes you were speeding or no you were not speeding. End of story.

Therefore any testimony that suggests you were speeding, even 1km/h over, is testimony against yourself and you might as well have just paid the ticket up front and not wasted your time coming to court.

My exeprience from going to court with Highway Traffic Act Provincial Offences is that 95% of people that testify, end up helping the prosecution and not themselves. And many wins that I have seen, did not involve the person testifying... it was all about bringing reasonable doubt to the officers testimony.

Read this:

http://www.ontariohighwaytrafficact.com/topic7032.html

If you choose to take the stand, here's something similar to what might me said.

CP: So you were speeding 72 in a 50.

SR: No, I was doing 59 in a 50.

CP: How are you certain you were doing 59?

SR: My speedometer said I was traveling at 59 km/hour.

CP: Is your speedometer a digital speedometer, or analog speedometer?

SR: It is analog. (95% of cars is analog)

CP: In what increments does the speedometer go up by?

SR: Increments of 5 (Most cars go up by this)

CP: so it is your estimation that you were doing 59, because your speedometer doesn't give an exact reading?

SR: (Unless your willing to purge yourself/DONT DO) Yes I believe that I was doing 59, based on my estimation.

Now if you have a digital gauge, the crown prosecutor count swing things like:

CP:When was the last time your speedometer was calibrated.

CP: Are your Rims/Tires factory issue? (can affect speedometer reading)

CP: Were your tires properly inflated? (also affects speedometer reading)

Most likely you cannot prove any of these facts. So in the closing statements, the crown prosecutor would say that how the officers reading on the lidar/radar is more accurate than that of the defendant (pre testing, certifications, etc) therefore the charge should be speeding 72 in a 50 rather than 59 in a 50.

That's why JSherk is recommending to NOT TESTIFY.

I just want to add that I completely disagree with absolute liability offences.

The Ministry and Police talk about safety and speeding together all the time, however when charged with speeding you are not given the opportunity to prove whether you were driving safely or causing some kind of danger to others. If I am driving on the 401 going 130km/h on a straight dry stretch of road with light traffic, there is nothing unsafe about it.

So I am not trying to deter you from fighting your ticket, I am just warning you about how the system works with these types of offences.

I have an issue in general with charges that involve no harm or damage as well, but that is another story.

rank wrote:

BTW, The Stig, I replied to you by PM. Not sure if it went through or not. Still learning this message board format.

Your PM did not come through.

It ain't the dang radar that's in question. You folks actually think that a police officer's testimony of when he pressed the radar button trumps physics? Guys, I appreciate the advice but forget about MY case for a minute. Don't get hung up on whether or not I can bring reasonable doubt.

Let's say a defendant admits to speeding but could produce irrefutable evidence that he was NOT doing 72. He can even prove beyond any doubt that he was doing less than 65...i.e. lesser fine and no points. This defendant does not even need a speedometer to prove it. And this defendant is guilty of 72? I can tell you what, if that defendant is guilty then his case should go all the way to the highest court. You may as well suspend the law of gravity in favor of police testimony of when he pressed a stupid button because that is what we are talking about here.

Again appreciate the help. He can press the button any time he wants. He can drive around all day with 72 on the radar. They can use dash camera video to capture the button push but they don't. WHY? Gotta love the Ontario court system has everyone brainwashed into thinking one man with a button is GOD. LOL.

You have peaked my curiosity...In this matter, what would the "irrefutable evidence" be? The courts will consider any evidence you put forth, whether they are buying what you are selling is the big question.

Again I love that you want to go after it the way you do. But you have to play by the rules of their game!

If you have an EXPERT WITNESS bring the "physics" testimony then you definitely have a chance.

Could you pull it off yourself? Well possibly. But you have an uphill battle in trying to convince a JP if you are not considered and expert in the field. Again it is possible, but you had better have a really really really good presentation.

And in the end it is up to the JP on how much weight they give your testimony versus the officers.

This is our great canadian un-justice system... please leave your common sense outside the court room!

Screech, I'm sure you understand that I'd rather not sent the crown a telegram detailing my defense. I've tried to be vague as possible.

If I am granted a new trial, I suppose this is a discussion that myself, the crown and the judge will need to have.

1. Here are my qualifications...do you consider me an expert witness?

2. Can I put myself on the stand as a expert but not as the driver?