Police radar, how does it work

[Deezul1]

Well it had to happen but it was prolly one of the few times I wasnt speeding. 20 mph School zone, light turns green me and a van leave the light and the van is slowly getting ahead of me. I go through this area 2or3 times a day and am very good about keeping school zone speed limits (not so good other places). The cop is standing in the bushes with hand held radar and then steps out into the street, holds up hand to stop and flags us to a side street where 3 other cops are writing them up fast as they can. the radar guy doesnt write any tickets at all. I was prolly going 23 mph and got wrote for 30. I believe the radar got the guy beside me so they wrote us both.

Is the radar broad beam or pin point, can it seperate 2 cars side by side for different readings, going to court but need info .

TIA

John

 

[socal_rattler]

It is my understanding that there are two different types the cops use, only one is a true radar.



The first (radar) uses radio waves which it sends out and reads the reflection back from a struck object. It is my understanding that this type probably cannot accurately determine which of two objects it is giving a reading on if they are relatively close together. (do your homework though before going to court!-JMO)



The second type is actually a laser. This is very accurate. The light beam is directed onto a specific object, so you do not have the 'spread' problem that radar has.

 

[paccool]

If he was in the brush, I've been told that can mess up the readings. So can going around a corner when they hit you with the signal.



Stan

 

[Bill Lins]

On a true radar (radio waves) the "beam" is cone-shaped. Its coverage spreads out as distance from the unit increases.



It reads and measures Doppler shift in the reflected return from the target. It is not nearly as accurate as most people and officers think. It is almost impossible for it to discriminate between two vehicles at much more than point-blank range.



It will also sometimes read an object behind the target if that object is much bigger than the target. Think of a semi a half-mile behind a VW. What do you think the radar is reading?



Also, as the angle from the unit to the target increases, the accuracy falls off- it's called "cosine error".



Hope this helps. P. S. if it is a laser unit, you're pretty well screwed. Sorry.

 

[Koa Man]

Laser is more accurate and easier to defeat than radar. It is possible to jam laser, I have had my jammer tested by a police friend. For good info, check this website: http://www.radar.co.nz/usa/usintro.html

 

[JohnMcIntyre]

Radar/Laser FAQ





Hmmm, sounds like there should be a grass roots revolt and everyone in the lower 48 should have one of these suckers... check out my previous thread in this Forum.



How does Radar work?



Police radar transceivers including GATSO cameras operate by sending out radio signals at a set frequency, which are then reflected by the target vehicle. The reflected signal's frequency is shifted in direct proportion to the vehicle's speed and this shift is used by the transceiver to calculate the speed.



How do Snoopers detect Radar?



A radar signal is essentially conical in shape, much like a flashlight beam. At 200 yards, which is incidentally the operating range of most radar guns, the signal is as wide as a 4-lane highway. Most of the signal therefore goes past the target and on up the road, reflecting off cars, trucks, trees and houses etc. eventually becoming "radar scatter". Snoopers are extremely sensitive radio receivers tuned to these particular frequencies and can detect very small particles of "radar scatter" at upto 2 miles.



Are they legal?



This depends upon the prevailing local laws in your part of the world. Meanwhile over here in England - following an Appeal Court ruling in January 1998, it is now fully legal to own and operate a Snooper. The 1949 Wireless Telegraphy Act previously used by the Police has been proven not applicable to Radar Detectors after a judicial review case brought forward by the Queen's Bench Divisional Court. Elsewhere in the lower 48 other states and part of the world... . in my experience a traffic ticket is pretty hard to beat most anywhere



How can you detect a GATSO camera?



Although GATSO cameras face away from the traffic and operate at a very low power, they still send out "radar scatter", which can be detected by a snooper, albeit at a very much reduced range. The next generation of MiniGATSO cameras aka the handheld hairdryers are portable and can be connected to a camera but operate on a different frequency - Ka band. They also face towards the traffic, thereby increasing the detection range.



What is Laser?



Laser guns project an infrared beam which is again reflected by the target vehicle. By timing those reflections, the laser can determine the target's speed. Laser beams although smaller than radar are also conical and scatter in much the same way. Laser scatter can also travel many miles and can still be detected by Snoopers, which use an off-axis detection system with a correspondingly wide arc of detection.



What do I look for in a good Radar/Laser detector?



Most manufacturers of combined radar/laser detectors generally use one Mixer to detect X-band and then rely on the harmonics or echo of that mixer circuitry to pick both up the K-band and Ka-band transmissions, simply because it's one of the easiest and cheapest ways to detect these frequencies - like taking a photocopy of an original photograph, you lose definition and the further up the bands you go, the worse it gets resulting in reduced sensitivity and delayed warnings!! IOW, a good combined radar/laser detector should ideally use a fundamental mixer for each frequency, ensuring sensitivity across all 4 primary radar frequencies, without compromising range.



Facts not hype!



Hmmm, sounds like there should be a grass roots revolt and everyone in the lower 48 should have one of these suckers... check out my previous thread in this Forum.

 

[joel]

OK, I'll chime in here with my . 02.



If you were beside a van and it was going faster, I believe the speed of the van is the one the radar gun displayed for 2 reasons. First, a bit about radar. Police radar guns are doppler radar devices and contrary to a previous post, are very accurate in their speed determination. They have a relativaly narrow beam width, but even so, I don't believe it's narrow enough to pinpoint one vehicle. So, what did your cop see? The van, being bigger probably had the stronger return into the gun and therfore his speed was displayed while yours was suppressed. Also, I'm going on rumor here because I have not seen this in writing, I believe the police speed guns are defaulted to show the faster of two returns speed if it receives 2 valid returns. Of, course, the problem remains here that you have to convice a judge that there was indeed a van and that he was going faster than you were.



Another tactic you can try is that they can't write the same violation for 2 people. You said the cops wrote both you and the van up for one radar hit. That means they don't know who was speeding, so if you guys were to team up, you might be able to get the judge to toss 'em both. If you just go by yourself, you again have to convice the judge that there was a van there and only one of you was speeding (not you, of course!) and the cops didn't know who, so they wrote both of you up. Very illegal, actually, for the cops to cite 2 different people for the same offense (assuming, of course, only one offense was committed). I'm guessing that the cops are betting on apathy that you'll both just pay the ticket and be done with it. Not a good idea, especially in a school zone according to my insurance company.



Go in, use both of these tactics, look the judge in the eye and stand fast that you were only doing 20-23 while the other guy was accelerating ahead of you.



Radar qualifications: Electronic Countermeasures Officer flying EA-6Bs, the worlds best (and only) tactical radar jamming aircraft!

 

[Big K]

In this state, this one is easy to beat, guilty or innocent. Problem is, it still requires taking the time to go to court. Here, the officer is required to show you the radar. If it has been cleared, or used since, there is no evidence. Exactly same thing happened to us, radared the lead car, and waved in several. Went to court, the judge scolded the officers, and dismissed w/ no court costs. Situations like this cause me some frustration. I wish to respect those who protect and serve, however, when they precipitate an illegal and unwarranted act, usually using a great deal of manpower to do so, I begin to lose faith. Bust the drug dealers, thieves, and murderers, not the contributing members of your community for doin' 5 over. Good Luck.

 

[Hale on wheels]

If the van was ahead of you it most definately picked up the van and not you. The farther the radio waves travel, the more loss occurs in the signal level. As someone posted above, the van had a higher signal level and the gun would have picked it up. The radars cannot disinguish between two different targets side by side. But if there was distance between you and the van, and you were fairly close to the cop, he could tag you both and read the speeds separately.

 

[Max340]

Having defeated this type of device in court, I'll tell you what I found out, maybe it will help you.



Beam: Is approx 10-15 degrees of spread. Range is said to be about 1320 feet. This is affected by many variables, but is generally true.



Method of measurement: The gun checks the shift in frequency (Doppler effect) of the transmitted wave compared to the reflected wave.



Cosine effect: This effect is the deviation of reading that happens with a deviatioon of the aim of the gun. If the Gun is aimed parallel to your direction of travel, it is not affected by the cosine effect. As the gun is aimed at more and more of an angle to the direction of travel, the cosine effect causes a lower and lower reading of the actual speed. IOW, cosine effect works in your favor. DO NOT MENTION IT IN COURT.



Gun design: The radar gun is designed to lock on the fastest object. NOTE: It does not differentiate between size of objects, it picks the fastest one to create the reading. IOW, the gun is looking for the largest shift in frequency, NOT the largest object or strongest return.



Calibration: in PA, a radar gun must have certification within 60 days of operation by a certified testing station. I suspect it is similar in other states. It must also be field tested. This test is generally done by using a tuning fork supplied with the gun. The fork is struck, and held in front of the gun, creating a reading, which should match a specified MPH.



Points of defense:



1) Since the width of the beam is best when 10-25 degrees in width, at 150' from the gun, the beam is 50' in width. In my case, the cop was claiming I was anywhere from 500' to 1320' feet away.



2) Because of beam width, the feature that allows the gun to track the fastest object also makes the gun less able to select one target.



3) Accuracy of the radar drops to as low as 71% at the edges of the beam.



4) Radar will not penetrate objects. If a tree is in the way, it causes a reading, assuming it moves at all. (more on this later)



5) Demand proof of certification of the radar unit in court. If they do not have it, the gun is immediately lacking in credibility.



6) Demand proof of field testing. It may be accepted by the court if the officer simply says he did it. Force him through questioning to detail the testing method. (how do you field test a radar gun, officer?)



7) If the tuning fork, which produces a reading moves less than an inch (Ever see a tuning fork? Bet it sat right still in your hand while it vibrated. ) Is it possible for the radar to pick up any other object in range? (answer is, YES, but the cop will deny it, he did in my case) FACT: If the tuning fork causes a reading, damn near anything will cause a reading, and the radar will report its speed very accurately.



8) Look for possible interference in the reading, other vehicles, large signs, leaves on trees, etc.





Not sure what else I have... . I can tell you I won the case I argued with this information.



Good luck.

 

[Bill Lins]

Originally posted by joel

Police radar guns are doppler radar devices and contrary to a previous post, are very accurate in their speed determination.

Yo, squid- go back and re-read my post. I was referring to the ability of the radar unit to discriminate between targets, and the post was clear in this regard.

 

[Bigsaint]

Most of the above is correct. We use only Doppler radar. In order to run radar, we must test the radar unit twice, once at the begining of the tour and once at the end of the tour. There are six tests performed on the unit each time... Internal circuit, light test, stationary mode with the 35 MPH tuning fork and then the 80 MPH tuning fork, a moving mode test using both the 35 and 80 MPH tuning forks and a calibration test while moving, to ensure that the readings on the 'Patrol' window of the unit are the same as the speed readings on the certified speedometer. The results of these tests are written on a 'Radar Log', which must be present if a summons is issued for a speeding violation.



There are four certifications that must be present in a trial, here in NJ. They are as follows... tuning fork certs. for both of the forks, speedometer cert. for the vehicle used ( only if the summons was issued in 'moving mode'), cert. for the officer that issued the summons which indicates that he/she has been trained in the proper use of Doppler radar.



Part of our training and yearly re-certification requires that we are able to judge the speed of a target vehicle, while the patrol unit is either in moving mode or stationary mode, day and night. We must be able to judge the target vehicle's speed within 5 MPH, which is then confirmed by the lock on of the radar.



If you are going to court to fight a speeding summons, another item to consider is the zone of influence, i. e. , were there other vehicles either A) behind you in either the same lane as your vehicle, or B) next to your vehicle in another lane of travel.



Doppler is not as 'target specific' as Laser radar. If there were other vehicles within the zone of influence, the officer must be able to clearly state why he/she issued the summons to your vehicle, this is why we are taught to be able to judge vehicle speeds within 5 MPH without the use of radar.



This being stated, if all of the above are intact and the officer knows how to testify, you will, in all likelyhood, lose. BUT... there's always a BUT , if you believe that you were issued a M. V. summons without merit, go ahead and fight the summons. I have seen many officer's lose radar cases because they absolutley $ucked on the stand and lost all credibility.



Scott W.

 

[Amianthus]

Pet LE Peeve.

There is some good information posted above. I would like to add a few more things to consider.



First, if he says that he used a "laser targeted" radar, don't even buy it as accurate and continue to go to court over the summons. There is a fellow in LaCrosse that likes to tell people that he used a laser to get a speed on the target vehicles when it is actually a radar gun that he used with a red-dot target sight attached to it. I won't tell you what I think of him.



Second, Radar must be certified for use in that area. By that I mean radar can't be used anywhere. There may be interference from certain objects in the area that will cause in accurate readings. Some of these objects can be factories, power sub-stations, radio stations, cellular phone towers, trains, chain link fences, the list goes on and on. A certification of an area for use by radar means that most (not all) of the time an accurate reading can be obtained on a moving target without outside interference. Make sure you look into this also.



Third, In addition to Big Saint's comments on what are required certifications that need to be presented in court, in Wisconsin (See Wisconsin VS. Hansen), the maintenance records for the radar unit are also required. Most of these records are seldom brought to court as there is a very cavalier attitude from DA's and officers about speeding summons. Make sure that all information is presented and don't leave anything out.



Finally, Some points on laser. Laser must be used from a stationary vehicle. That and it must be as close to parallel to the target as possible. Otherwise you'll get the same cosine error that was described above.



Now for the oipinion part. Plug your ears. No officer should ever be given a radar to use for speed determination. They should be issued a laser unit to use. Laser is FAR more accurate and fair. Unfortunately they cost too much for most departments. I've also found that most officers are severly under-trained in the operation of radar of any sort. They are given a short class, given a radar speed detection device of some sort and sent out. Most don't even know what factors can influence a radar return on a target, or even how wide the beam is on the device they are using. This is truly sad. Traffic enforcement has become a multi-million dollar industry for some municipalities. And as such, money is the motivating factor, not LE and justice. Some affectionately refer to this type of enforcement as a reverse-lottery or a driving tax.

And I don't care what anyone says about quotas. You can't tell me that someone who issues a slew of summons will lose a promotion to someone who issues fewer summons.



Unplug your ears now, I'm done ranting. If I keep going, Ken is going to have to allocate a new server just to handle my tyrade on this topic. Take what I said in the last paragraph with a grain of salt as I'm very passionate about this topic, and can get out of my head sometimes. Good luck with your endeavor to seek justice. In some places, you'll need all the luck you can get.

 

[illflem]

Amianthus, Since you are saying that radar must be stationary in order to accurate, is the speed device I sometimes see hanging from the drivers door of a patrol car laser or something? I've never been pulled over but have had an officer approaching from the other direction signal me to slow down, I find it hard to believe that while he is coming at me at 60 mph that he can tell I'm going 70 just by looking.

 

[Amianthus]

Not quite

No. Only Laser must be used from a stationary vehicle. The unit you see is a classic radar unit.

Mobile radar works like this. It sends out a low frequency towards the ground. That is the patrol speed. It then sends out a frequency for the target speed that is much higher. It then calculates the difference in speed and displays it as a target speed. Good theory, not great practice.

If the radar equipped patrol car is in traffic, the low frequency signal can bounce off of a semi, a car or other object that is not the road. This will cause the patrol speed to be erronious.

Second, the officer must know what he is shooting while he is driving. IE he must be able to tell what the target is as the radar unit cannot. These problems were brought up before.



Use of radar in a moving patrol vehicle is an almost super-human task. Follow this example. A patrol car is moving at 65 mph east bound on an interstate (flat, good weather, no obstructions, divided). He sees what he suspects is a speeding vehicle approaching west bound at say 80mph. Now the visual range is 1/4 mile. The officer now has to aim the unit into that traffic. Ensure there are no obsticles that could give a false reading. Activate the radar. Ensure that the patrol speed noted on the radar console matches the certified speedometer in his patrol car. Checks the target speed was attained. Check that the target speed changes when the target vehicle leaves the radar beam to verify that it was indeed that target vehicle. Stop the patrol car, turn it around and pursue the offender to issue a summons. THAT ALOT OF STUFF TO DO IN 1/4 MILE!!! So errors can and do happen. It's not the fault of the officer. Not entirely. It's the fact that we allow them to use this crappy equipment.

One other thing about radar I cannot stand is this audio doppler crap. Or the (I forget the term for it) target lock garbage. Basicly, it works like this. The officer parks his patrol car and points his radar gun out the window. He set the threashold speed and turns it on. When a traget hits the threashold speed it alarms. Some people do paperwork while the unit is operating, or other things. So when they look up, the first car they see is sometimes who gets picked. Audio doppler varies in that it has a scaled tone. So the faster the target the higher the tone.

But this gets back to the officer being able to estimate the target vehicle speed. Some guys are very, very good at it, some are not. It is just an estimate. He may not have been able to tell that you were doing 70, just going fast. Which was enough.

Anyone have anything else to add? Or howabout some criticism for my opinion. I won't mind. Promise.

 

[Max340]

Amianthus, no criticism here, I have seen proof of what you say many times. The Trooper opposing me in court told me he was certified to train other troopers to use the radar unit he was operating. But he did not know an exact range, a beam width (in feet at a certain distance OR in degrees), how the doppler effect was used, or that a tree could in fact be clocked and get a reading.



Saint, I am amazed (and pleased) by the amount of documentation you must haul into court. Here in Pa, a cert showing the unit was calibrated within 60 days is acceptable by the bench as proof that the radar is operating properly. Nevermind storage time, possible jolts from transit, or even misuse by the officer, who does not have to show a cert of ability to operate the radar. It may be harder for you in the event of a court appearance, but it definitely makes the process more accurate.

 

[Deezul1]

Thanks for all the input guys, keep it coming. Knowledge is power and I need it. If I had it coming I would just go to traffic school and be done with it but for once I am not guilty and will fight and hope with you alls help maybe win.

Can anybody from Texas tell me, can you still go to traffic school and keep it off your record if you lose in court?

Thanks

John

 

[Bigsaint]

Amianthus, again, some good points. I forgot about the maint. records. Yep, we need them as well.



Bottom line, the Doppler radar is only as good and accurate as the operator, and that does leave alot of room for error. Like I stated in my last post, half of the battle in court is credability and I have seen more than a few officers fail miserably when up against a good attorney that tries radar cases on a regular basis. It all falls back to the training issue. We are given basic radar instruction while recruits in the academy. Basic radar is all of two 8 hr. blocks of instruction. After a recruit graduates, they spend 12 weeks with a FTO (Field training Officer). The recruit must complete 80 hrs. of actual field use of the radar in all modes and must display a proficency in same. We teach them on the road, the errors of batching, scanning, panning, etc. and how it will affect their target speed.



Long are the days, at least for us, of the old, constant on radar that you spoke of, that always emits a signal and the officer can set to alert when a tracked vehicle goes beyond the set target speed. We use instant on radar. The basic prinicple of instant on is to observe the target vehicle first, estimate it's speed and then activate the unit while observing the target vehicle's speed on the unit and the corresponding doppler pitch or tone, if you will. The higher the pitch of the doppler, the higher the rate of speed for the target. All of this, the estimated speed, the target window speed and the doppler pitch must be correlated in order to indicate that the target is in fact operating at the speed indicated by the radar. Vehicle shapes, the terrain, weather, other traffic, etc. , all come into play when operating radar.



As for the moving mode issue, we don't live in a perfect world. It is my opinion that moving Doppler radar can be as accurate as stationary, in my experience. Again, it's all about the operator and his experience and professionalism that are on the line. Moving radar is used by us in many areas where it is just not practical to set up a stationary post, i. e. , lack of target visibility, lack of an adequate location to park, etc. he main problem, from a enforcement stand, with stationary radar is the visiblity to the public. Most drivers warn the other drivers of the stationary post through the use of headlamps. Now, this might be a great thing for the motoring public, but it can get real frustating for the cop, who was sent to a specific area after receiving complaints from the residents of that area in regards to speeding vehicles. IMHO, laser radar is only real useful when enforcing the speed on major highways, where there is a lot of traffic and the sight distance is large. If I tried to set up a stationary radar post in my town in the daylight hrs. , regardless of laser or Doppler, the impact at reducing speed through issued summons would be low at best.



I liked what you stated about the summons and quota's, no doubt about it, they will directly use the 'count' when looking at canidates for promotion. Makes me sick, but it's true. They don't even look at the conviction rate, which would at least indicate that the officer in question was either A) writing a ton of summons without merit or B) a good radar operator that uses common sense and good judgement when issuing.



Personally, my day usually invloves answering calls for service, very little time for routine patrol or radar operation, I can't even remember the last time I turned the unit on. I eat dinner cold and in several sittings on most days. These days, unless you live in the town of Hazzard, with the celebrity speed traps and handheld hair dryers disguisted as radar guns, that's the way it is.



Scott W.

 

[Max340]

Saint, you say that drivers warning others via headlights is frustrating, but doesn't it have the same effect as writing a ticket, only more people slow down than just one? IOW, isn't a visible deterrent as good, if not better than a fine handed to one person?



Maybe I am wrong, but it seems to me that if you have people adhering to the law AND you don't have the trouble of a traffic stop, it makes doing the job a heckuvalot easier.

 

[Amianthus]

'Saint, your seasoning as an officer really does shine in this thread. (I mean that as a compliment)



You stated a few things about traffic radar that I want to re-enforce. One was all of the factors that can come into play in getting a radar return on a target vehicle. There are many things an officer must look for like you said. Vehicle size, speed, shape, vehicles beyond the target, obstructions, any other possible interference. That's alot. So much that I believe that it's all but impossible to do. It sounds like you are at least making an effort to ensure that errors are kept to a minimum. That should be commended.



I've heard estimates that 25% of speeding summons are written in error. I don't know if it really is that high. Maybe 15-20%. But still, it's higher than it should be and higher than it needs to be. Basicly 15% of the motoring public is getting screwed. That's a truckload of mis-levied fines and points. That is pretty sad.



I guess I really didn't think about the application of moving radar. I just hate radar in general. And am looking for something that would be less apt to involve errors. Laser seems to be that ticket (no pun intended).



Service calls. My town is lucky enough that we really don't have a whole lot of people who regularly complain. You know the type. So they do traffic enforcement every so often. Now some neighboring towns, get complaints for everything. I wish that the Police would just tell them to dry up and go away for some of the petty crap they call for. But that wouldn't be very PC now would it. Cold dinners, yeah I've had my share too. Not as many as you, but I know it sucks.



Deezul 1, check out the link below. You can look up every statute in your state. It may take some digging, but you should be able to find out about the laws of discovery (Wisconsin traffic court doesn't allow for discovery, so you don't get anything from them), trafic radar use, and traffic laws. It's actually pretty neat when you want to look something up.



http://www.capitol.state.tx.us/statutes/statutes.html



Hope we helped. If not, let us know.