Pizza's Radar Thread
 

A few nights ago Deb Walker and I were discussing our cars (what else?) on Yahoo Instant Messenger. At one point, the discussion turned to police (traffic) radar. I realized something: not everyone does what I do for a living and therefore does not know some of the “ins and outs” of traffic radar. (Nothing gets by me. :rolleyes: )

I then made up my mind that it’s been too long since I wrote anything. Perhaps, it is time to attempt to keep my writing skills as sharp as my English professor said they were in 2008. (It should be noted that he IS a marijuana user, so don’t expect too much here.)

I am not writing this in order to help anyone avoid the law; I am doing it more for the writing experience – and the fact that Deb found our conversation interesting and maybe some of you here will, too. Besides, speed alone is not usually what causes accidents and we all know that. There are places where doing 89 in a 70 zone will pose no great threat (like an interstate with little traffic). On the other hand, if I was a police officer and caught you doing 35 in a 25 zone while passing an elementary school, I’d not bother with a ticket – I’d just kick your dumb, selfish ***.

So, what makes ME qualified to lecture on radar? Well, contrary to what you might think, I don’t make pizza for a living. In fact, I should be called “radioguy”. At this time, I have 29 years experience in radio equipment repair and maintenance. For the past nine years I have also been doing land mobile system design as well as State-of-Georgia-compliant radar certifications. (That ticket the officer just wrote you won't stand up in court, unless he has my signature and FCC license number on a calibration certificate, dated within the last year.). I also hold two FCC licenses; an industry technical certification known as a “CET” and recently (after all these years) earned a degree in electronics with an emphasis on radio communications.

Remember, you can call it radar, television, a cell phone, AM or FM - anything you want to - it’s all just different applications of radio. And I am "radioguy".

What I will write is based mostly on technical knowledge. But it is also based on interactions with officers when they complain that their radar “is acting up” or “doesn’t do this or that like it did when it was new”.

I also have carried a Kustom K band radar in my van for many years as an “operating spare”. Having this thing with me has proved very interesting. It has also helped me to understand some of the complaints that officers bring to me about their radar units.

This will be hard to explain without pictures, videos, power point slides or the ability to see the look on my handsome face... so I will break this up in sections and TRY my BEST to be clear.

Re: Pizza's Radar Thread
 

Police or traffic radar uses the “Doppler” effect to measure speed. You have heard this effect as an approaching vehicle with a siren went flying by you. It seemed like the siren tone changed as it passed by, didn’t it? Now, you KNOW it didn’t change, but as the vehicle came at you, the sound waves of the siren were “speeded up” by the speed of the vehicle. If you “speed up” sound, it is the same as increasing its frequency or ‘pitch’. After it passed you, the sound waves were “slowed down” by the same movement. Your ears hear these changes as changes in pitch.

Radio waves can go through a similar process. Say officer Fife is sitting in his car alongside the road. His radar unit is throwing out a constant beam of microwave radio energy. (Think of "microwave radio energy" as a kind of sound wave... just for the moment, ok? Think of it like the siren in the example above.) This beam is reflected by the ground, trees, signs, etc. All these objects are stationary, so the reflected wave is of the same frequency as the wave that was sent out. The radar senses this reflected wave and uses it as a “ground reference”. With Fife’s car stationary, the ground reference plays only a small role, but it plays a fundamental role when he is moving. (More on that later.)

Now, along YOU come, doing 70 mph (which is a bad thing because the speed limit is 45). The radar is hitting you and bouncing back. Because you are moving toward the radar, the radio waves have picked up speed by the speed of your moving car that they bounced off of. This means they are shifted slightly higher in frequency. (In fact, with a Ka band radar operating at 34.2 gHz the waves bouncing off you are shifted up 7149 hertz.) The radar unit detects this shift and does some quick math and displays a “Target” speed of 70. But Fife is asleep.

Now, did you notice something? That 7149 hertz difference is in the audio range. Humans can hear a 7149 hertz sound. This 7149 hertz signal is processed and displayed as a speed of 70. But this signal is also amplified and sent to the radar’s speaker. This speaker comes alive with the SOUND of you speeding and Fife wakes up. But by the time he’s really “with it” you have seen him and slowed down to 45. He hears the tone going down in frequency (to 4600 hertz at 45 mph) and knows without looking at the radar that he has a target that sees him.

(We replace a LOT of speakers in radar units. They squeeze a little speaker into the radar head and then drive the heck out of it – so they do fail a lot. Now, in Georgia, officers are trained and REQUIRED to match the sound of the speeder, the sight of the speeder, and the display of the speed on the radar’s display. The idea is to make an absolute determination that the target is a real target and exactly WHO it is. If the speaker fails, the officer can’t testify that he followed procedure.)

As you pass by Fife, you keep a steady speed of 45. He switches to his rear-facing antenna. Since you are going away from him, the reflected waves are in effect slowed down by the speed of you moving away in much the same way as they were sped up before. They are now of a lower frequency than the original wave – but lower by the same amount as they were higher by before. This means that the SOUND in his speaker (the difference frequency) is the same – the difference frequency of 4600 hertz. And you are still under surveillance.


Let’s say that Fife is now moving along at 60 mph. Remember that “ground reference” reflection? Well, now IT is shifted up in frequency by the speed of the patrol car. What I mean is this: the radar now sees the entire world moving at it at the speed of the patrol car. Many radar units will recognize the change in the ground reference and automatically switch to “Patrol Mode”. The “patrol speed” display shows this speed. The “target” display is blank until…

Along you come, at 70 mph. The shift in your echo is now much greater, you are moving at him at the combined speed of your car and his. Your echo looks to the radar like a 130 mph echo. But the radar is in “Patrol Mode” so it does some easy math and subtracts the patrol speed (that is, the ground reference) from the indication it is getting from you. It displays your speed as the difference between the speed you and he are approaching each other at and the ground reference. The “Target” display shows 70 mph.

If you are coming up behind Fife’s car, and IF he switches to his rear antenna, THAT ground reference signal will show the world going away from the radar at 60 mph. But you come up doing 70. This means that the radar sees you approaching at 10 mph (the difference in your speed and the speed of the patrol car). But since the radar is in “Patrol Mode”, it adds the 60 mph of the ground reference and displays a “Target” of 70.

This leads us to an obvious conclusion: Science and mathematics haven’t been this interesting since you took that class in high school with the hot teacher!

Re: Pizza's Radar Thread
 

I know, I know… now my heading doesn’t make any sense. But it IS true. Radar does NOT, and can NOT, measure the speed of your car as it travels over the ground. Read thru the posts above and it will occur to you what the radar is REALLY doing.

What radar measures is your speed IN RELATION TO THE RADAR DEVICE, taking into account the ground reference signal. But why does this matter? Why would I bring this up? You have seen that the radar can do the math and display the right speed anyway, right?

Wrong – sometimes. But don’t despair that radar can be wrong: this has probably saved you from a few tickets. The fact is, you can be moving MUCH FASTER over the ground than the radar shows. You can easily predict when this is happening, and so can the officer. You are now about to learn that the old adage, "By the time you see the officer, he has you" is not always true.

Let’s say you are driving along, and Fife is parked up ahead just past a curve, finishing his morning donut and coffee. You are moving over the ground at 70 mph. Because you are traveling in an arc, you are closing on his position at less than 70 mph. His radar cannot calculate that you are moving in an arc, it displays the speed at which you are approaching him. If it’s a 90 degree curve, before you round the curve, you are BARELY closing on him and his display shows you doing a FRACTION of your actual speed. After you get out of the curve and are headed straight to him, he now sees your true speed. But you have slowed down to 55 by now, because you saw him while you were approaching the curve. He KNOWS you were going somewhat faster, but cannot prove it. You just avoided a ticket. (In Georgia, officers are not allowed to interpolate and write a ticket on what they believe your speed to have been.)

Why did you THINK that so many police sit at the bottom of a hill on a strait portion of road?


I have observed an interesting thing while carrying my radar around. I could capture a target breaking over a hill from as much as ¾ mile away, and then would lose the target until we got closer to one another. This seemed to happen more with certain cars, or should I say certain SHAPES of cars.

Cars like the Crossfire have a characteristic like the old Triumph TR7: they tend to be a bit invisible to radar. How so? Well, remember that “ground reference” I mentioned? As you can imagine, it is quite a strong signal. Now, take a look at our car’s front ends. Not much of a reflector, huh?Our cars (and many others) have a small profile as seen from the front. And MUCH of our “head on” profile is slanted, angled or tilted. Why is this important? Well, most of the radar energy that hits the hood and frame around the windshield is reflected upward at an angle due to the slope of the car’s exterior. This reflection bounces back towards the radar unit, but at an angle – going over Fife’s head and missing the radar antenna completely.

The reflection of our cars, what little there is that makes it back to the radar, can get lost in that “ground reference” I mentioned. What do I mean? See, the ability of the radar to discern the echo from your car is a function of the filtering ability of the receiver chain in the radar. This circuitry, like all electronic circuits, has some limitations. Detecting a small signal (from your car) in the presence of a strong signal (the ground reference) can be difficult.

When you break over the top of a hill, the officer down below gets a good echo off the front of the car and this echo stands out in the radar’s detector. As you come down the hill, quite often, your echo is lost in the ground reference until you get a bit closer. Sure, IF he is quick with the lock button, he’s locked in your speed and you lose anyway. But with a lot of traffic (which represents multiple echoes and additional ‘work’ for the receiver filtering), your echo can get “lost” in the noise. That is, until you get closer.

Older radars displayed, most of the time, the speed of the strongest echo. And this meant that the closest vehicle (usually) was locked on to. Sometimes, a big truck or bus would be the strongest signal, even if it was not the closest target.

But today, with the advent of digital signal processing and better and better filtering, officers have radars with much more impressive abilities. Radar can now provide officers with a “fastest” mode. This mode is intended to allow an officer to ignore the strongest echo (like from the cement truck ahead of you) and instead display the fastest target, even if it is smaller or more distant that others.

The officer can tell that you are zipping along faster than everyone else – now he can actually filter out all the other echoes and look at you by choosing “fastest” mode. So, don’t get too cocky just because you are surrounded by other vehicles.

I’ve heard this one before – that “someone” said radar can’t be trusted because it often clocks trees or road signs at 30 or 40 or more miles per hour. This is baloney. I don’t say this to imply that the display won’t sometimes display something odd – I say it because when it DOES display something odd, there is often no way to determine what it really is seeing. To say that it is "clocking a tree" is nonsense - you probably won't know WHAT the hell it is seeing.

And officers know this. Just because the radar says 95 or whatever AND there is nothing but a tree in the area, does NOT mean that the Radar “clocked” the tree at 95.

I said that officers understand this stuff, case in point:
We had an officer come in and complain that his radar often displayed an odd speed – something like 37 mph – at times when he was patrolling at 60-70 mph. There seemed to be no “rhyme or reason” to it. I took his car for several test drives before I saw the radar do it. The radar was operating normally – it was his patrol car that was the problem. I saw it as I drove down the highway. Just as the radar indicated the false speed – I saw an odd vibration. His “push bumper” had been removed for a front end repair. When the mechanics put it back on, they left 3 of the 6 bolts out. The loosely mounted bumper was vibrating and sending an echo of the vibration back to the radar! Adding the three missing bolts resolved the problem.

Another case was much easier to fix. “When I turn my Air Conditioning on, I get a constant target of 56 mph”. Sure enough, with the car sitting in our yard, you need only turn the A/C or heat on and set the fan to "medium" and there you had it - 56 or so on the "Target" display.

The shop that installed his radar had put the antenna a bit too far back from the windshield. The radar energy was striking the blower cage buried in the dash and bouncing back up into the antenna. It was measuring the speed of the blower cage! (This was also an officer safety issue. If energy is striking the blower like that, then too much energy is in the car, not a good thing when playing with microwaves.)

In any event, you did NOT get a ticket because of any of these issues. Officers KNOW intuitively that something is wrong when things like this happen. Believe me, they are quick to come in and ask us to look into such “ghosts”.

Re: Pizza's Radar Thread
 

One thing I wanted to show you was that the old adage, “by the time you see the officer, his radar has you” is simply not always true. There are several things working in your favor: multiple targets to sort out, curves that reduce your indicated speed, signal to noise ratios (or signal to ground reference ratios) that can delay the radar’s ability to lock on to you, etc. The fact is, it is often NOT too late to slow it down.

I should also mention that I have commented several times on what the law is. Or on what an officer can do or must testify to. My comments are based on Georgia State law and on past cases that our judges now use to determine how they will rule. When reading what I have written, please remember, these comments only apply to Georgia! I don’t know what the law is in your state – but I do know the laws of physics apply everywhere. (Everywhere other than on any sci-fi TV show, that is. :rolleyes: )

I’d also add that LASER works in much the same way that radar does. There is, however, ONE exception: LASERs are pointed directly at a target and aimed like a gun. The officer has no problem making a determination as to who he is targeting.

I asked the Post Commander of Georgia State Patrol post number one, in Griffin (my home town these days) a question: “Does LASER require less training than radar?” He had no problem forming an answer: "While we are required to attend school for laser, just as with radar, laser requires less training". Simply stated, he said that laser is very easily aimed. Knowing what your radar is telling you is usually more difficult.

I sure hope this effort has been easy to read and is understandable. It makes good practice for me, as one of my responsibilities is to write simple manuals for our customers to use. (They replace the awful manuals that some of the equipment we sell comes with!)

Re: Pizza's Radar Thread
 

I had some trouble with the text editor. I have proof read the above posts, but if I missed any errors, please let me know.

Re: Pizza's Radar Thread
 

Re: Pizza's Radar Thread
 

Wow.....Great write up and in terms my old crusty brain could understand !!
Thanks RadioGuy !!

Re: Pizza's Radar Thread
 

Now would you like Barney Fife's side of the story?

Re: Pizza's Radar Thread
 

Oh, HE!! yeah...:)

Re: Pizza's Radar Thread
 

Well, I TRIED to write it from his side in a way, anyway... since a lot of my information comes from officers.

Anyway, spending all this time on this, made a good diversion from the conversations with my sister over the past few days.

In my next thread, I will explain women. Stay tuned.

Re: Pizza's Radar Thread
 

Well, Max...since you asked, lol....Pizzaguy is correct, as a technician. All that he states is right on. Now to the real world. Like many things, a tool is only as good as its operator. To say a policeman doesn't always see you, so go ahead and speed, is like putting one bullet in your revolver and spinning the cylinder pulling the trigger. Sooner or lately, it will go bang. Those of us who have yrs of experience using RADAR, LIDAR, and the one he didn't mention, which is my favorite, btw, is VASCAR. You see not all Barney Fife's are a like...we choose different weapons for the job at hand. Just when you and your radar detector think you are untouchable, some ole' man like me just sets there patiently waiting for a visual of my intented target, at which time, Pizzaguy, I turn on my "tool" and begin, my "tracking history" of the target vehicle. This is important that I use sound, as mentioned, for the track. Most, and I mean Most officers find the sound annoying and don't use it. Big mistake in court, because, now you can't testify you actually "tracked" that vehicle. Back on point, I now have my tracking history as the car passed by my antenna. Off I go to have a talk with my suspect. He has a detector, but it didn't go off, well it went off, but my finder was faster than his foot, lol, because I never give my position away by turning it on and off to just check speed, but wait until I really have a violator. Sneaky, but effective. Now Pizzaguy, tell them about my VASCAR...

Re: Pizza's Radar Thread
 

Thanks, Doc. That is all I can guarantee.

I better go back and read my posts - my intent was to encorage people that they had time to cool it in many cases and that "by the time you see him, he has you" does not always apply.

I did not intend to say, "don't worry, he probably doesn't have you". Note that I shy away (in the other thread) about discussing radar detectors, Doc.

I know what you mean by that, but around here, Radar and Laser are all they have. AFAIK, even the GSP has only Radar and Laser.

So the courts around the country actually ARE similar in their handling of speeding tickets? (Not that I am surprised, but I KNOW you are not in Georgia.)

I wish this had come up in the other thread. Most people dont' understand that there is SO much more to issuing a speeding ticket than looking up at the radar display, seeing "89" in the target window, and going after the first car you see out your windshield. This was part of my argument with (someone) that when an officer issues a ticket, for the most part, he knows more about what he is doing than YOU do.

Do you remember that thread from about two months ago? I wish you'd said this then!

Re: Pizza's Radar Thread
 

Most atty's don't educate themselves enough about the proper use of RADAR, so a lot people pay fines for something they may not be guilty of, or couldn't be proven. In court, you have a 50/50 chance of winning if you know the right questions to ask. One, is the unit you used, certified, 2, how did you operate the unit for the day in question. In other words, did you at the beginning of your shift, check your radar for calibration? Which for the operator, is self, internal check, and tuning fork. 3rd, did you do this at the beginning, during, and after your shift. Better answer yes. As you know, there are a lot variables, angles, curves, objects, traffic, etc...No one in court ever asks those questions, unless they were trained...which I have done in my earlier yrs. Why, because no one deserves a cheap ticket. Officers should do their job. I have never lost in court in my 30 yrs, because I do it right...and so should others doing this job...nice read Pizzaguy...

PS....VASCAR...do you have experience with this unit, if so, tell the readers of this thread how it works...lol

If not, then you can read here.... www.vascar.com

Re: Pizza's Radar Thread
 

While pizzaguy is reloading....I want to ask all of you if you have ever seen white lines painted across the road for no apparent reason, or have you ever seen an orange construction cone setting out in the middle of nowhere along side of the road? It just might mean there is an officer in the area running vascar. All the officer needs are points of reference, known points. So, I can set an orange cone out along side the interstate, and then at 1000' up the road, I set out another for my points of reference. I just set back on an overpass out of sight, and clock the speeds of those passing the cones....no radio waves to detect, just a timing device...and you can actually use a stop watch for this, but the unit stands up in court. Some communities, and states will paint permanent white lines across the highway or street for the same affect. Just be alert when driving, do the speed inside of towns and cities, they watch alot closer....interstate, find yourself a carefree rabbit and follow him...he will get nailed before you...use to be able to hide along side the big rigs, but new radar, and lidar will get you now...so stay away from the semi...especially mine...lol I know this may be confusing, I am a semi retired police officer, who now trucks for a living...use be a full time officer part time trucker, the role has now reversed....happy motoring

Re: Pizza's Radar Thread
 

No, no experience.

We have one department that bought several, officers (as you indicated) didn't want to use them. AFAIK, they still have them, but they sit in a locker at the department, collecting dust. (Paid for with confiscated drug money, so no one cares).

I am intrigued, going hiking with the dog (in 43F temperatures :rolleyes: ), I'll have something to read when I get back!

Re: Pizza's Radar Thread
 

Hope you enjoyed the walk....and I might add, VASCAR is a favorite for the "eye in the sky" states that use airplanes, like Illinios..Indiana use to, but avgas is expensive to just write a citation...lol

Re: Pizza's Radar Thread
 

Back in Michigan, in the 80's, the story was that those marks (at the time) were for aerial traffic enforcement. And they probably were, back then.

Ever since, I have always "alerted" on them - again, that is part of my remark in the other thread about "knowing how" and that means "knowing when and where" to gamble with speed.... and where not to!

Headed to the trails!

Re: Pizza's Radar Thread
 

Good read Pizzaguy and Doc.

From the perspective of the speeder: the BEST way to avoid speeding tickets (except for not speeding at all) is to PAY ATTENTION! There is no replacement for staying sharp behind the wheel. Be intelligent. Keep you're eyes open and THINK!

For example: on my way to work every morning, I pass a weight station on the interstate. At the weigh station there is always a PUCO officer (they police the truck traffic in Ohio for weight standards, placards, and all sorts of things that don't really apply to typical passenger vehicles). But... there is almost always a State Highway Patrol car parked there too. What is he doing? Using radar on passing cars? Nope. He's getting a cup of coffee, talking to his buddies, or maybe doing some paperwork. In fact, sometimes I see up to four patrol cars there.

I know you're thinking: so what? Well, if there's four patrol cars sitting in the weigh station, how many do you think I'll find hiding in the bushes on the rest of my trip to work? If there's three there, I'm betting one is out there working - patrolling or sitting in a speed trap - or... actually assisting a stranded motorist. So just from that simple observation I can figure what my chances are of running into John Q. Law on my way to work.

Or, as you're driving along, you see people slowing down for no apparent reason. Well, that's your clue. There's a cop up there (or an accident or something dangerous) and you can't see him yet. But all those people in front of you can and they're slowing down. So you better too.

Or, there's an orange cone or barrel sitting out near the highway, in the middle of nowhere - no construction in sight. Hmmm... I wonder what that's for? LOL

Or there's a light blue car sitting in the U-turn, as if he's trying to turn around... no, it's an unmarked police car and he's radaring you. DUH!

Or you're coming up on a place that you think would be perfect for a LEO (law enforcement officer) to sit with his trusty radar gun... so slow down! If you think it's a good place, LEO prolly does too.

Sure there's lots of other ways too. But the point is: keep your thinking cap on and pay attention!

In my opinion radar and laser detectors are dangerous. They can lull you into a false sense of security and let you think that you don't have to pay attention. Well, if you're speeding, you had better be paying attention anyway! If you're not, you shouldn't be driving.


LEGAL DISCLAIMER: If you speed because of what you read here, you are an idiot and I take no responsibility for your actions. Speeding is against the law. You should obey the law.

Re: Pizza's Radar Thread
 

Tom, and this is coming from a friend, you need to start practicing the above....lol....

A side note: detectors will let you know there is a LEO in the area working, IF, he leaves his unit on. It's the one who looks for his violator, by visual, with his unit in standby mode, that will get you, but while he is getting you, others with detectors will be alerted he is in the area, if this make sense. I took one to the dragon this yr. It will let you know they are up there working...that's all they are good for....keeping yourself in check...

A Trooper friend of mine had this plague on his dash: Sometimes you get the bear, Sometimes the bear gets you.

Re: Pizza's Radar Thread
 

So may good responses by Doc, and so many others.
This one is my favorite - because writing the OP's is practice for what I really want to do career-wise. :cool: