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  1. #1
    Join Date
    Jan 2009
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    Default How is Radar Affected by the Police Driving Speed

    This is for the state of Arizona:

    I am just getting slapped by a run of bad luck. Anyway so I have some record of the facts I thought I would post here.

    I was driving south on a 35mph street and saw a police car coming north toward me in the distance about 1/2 to 3/4 of a block. So because I had gotten a ticket recently I was checking my speed most of the time and every police car was standing out. So I look down and I’m going 38mph and while most cops would not cite for that I tap my brakes anyway and slow to under 35 just a tad.

    I'm heading south in the curb lane and h is heading north in the lane next to the center turn lane.

    He turns and come up behind me and light go on.

    He walks up and asks for the usual and I’m fuming wondering WTH could this be for????? I even asked: What is this about??/

    He leaves comes back. Ask do I know what this is about
    I respond umm that’s why I just asked you that no I don't.
    Officer: what’s the speed limit here on Campbell?
    me: 35.
    Officer: how fast where you going?
    me: 35 maybe a little over.
    Officer: well I had you clocked at 51.
    me: !51! there is no way I was going 51 I know I wasn’t.
    Officer: that’s what I had you clocked at.
    me: I was not going that fast I would have had to been flooring it and I know I wasn't.

    he walks away.

    He comes back starts the yadd yadda yadda so I cut in
    me: I'm sorry I was not going no 51.
    him: I’m not going to argue.
    me: do you have a dash cam?
    him: a what?
    me [ i think this is bs how can he not know what a freaking dash cam is] you know the camera on your car that record like on those video shows?
    him: no
    tit for tat some more he starts to leave I wave him down.
    me: do you still have the reading on the radar
    him: no, it doesn’t matter it is dash mounted
    leaves again
    I flag him one last time
    me: I want to ask you what direction you were going and stuff and record you on my cell phone camera.
    him: that’s what the hearing is for.
    me: so there is nothing on this paper saying anything about where or what you were doing and what we go to court and you can just say anything.
    him: If you think I’m lying you can contact internal affairs.
    me: you have their card.
    him: you can look it up and you have my name on the citation so unless you have an emergency I’m going to leave this scene.

    So sorry for the play by play but I want to print this for courts since apparently months later a police man is supposed to just remember where he was what he was doing and since he was driving toward me how fast he was going not that that has an effect which is the point of my post and questions:

    1. Can dash mounted guns which from the sounds of it are non removable be rotated or what is the cone of effectiveness and range?

    2. If a car is heading south at 38 and a police car is heading north at an unknown speed can a radar gun give an incorrect reading since both vehicles are heading toward each other?

    3. In regards to 1 what could this mean a radar tag on one car though the officer may be looking elsewhere?

    4. Oh and do they take or make notes on the copys they have? I mean if he comes into court and says I was sitting at the side of the road taging people as they went by and tagged this guy and I have a freak out so what I just look crazy and there is no notetation that has a record? I mean can they just come to court and say anything?

  2. #2
    Join Date
    Aug 2006
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    563

    Default Re: How is Radar Effected by the Police Driving Speed

    Some of radar's shortcomings are readily apparent. Beam Width is one. Think of a radar beam as a cone - narrow at the radar antenna and widening as it heads for the horizon. Even the narrowest of radar beams - 11 degrees - is 38 feet wide when 200 feet down the road and 57 feet wide at 300 feet away. Some radar units transmit a beam as wide as 24 degrees. By the time a radar beam is several hundred feet from a patrol car, the microwaves are blanketing an area as wide as an expressway.

    Now picture that expressway full of cars and trucks, and remember that traffic radar can't tell its operator which vehicle it is monitoring, or whether the target is approaching or traveling away from the police car. You quickly understand how great the potential is for misidentification.

    Let's throw in another twist or two. Even though police radar is based on the Doppler Principle, most units do not interpret the Doppler shift itself. Rather, they process the frequency of the signal and use its analog to represent target speeds. Known as phase-lock loop, or PPL, this processing can lock onto the wrong target, double or triple low speed readings, or produce "ghost" readings. Other types of common radar errors are:

    1.Radio or Microwave Interference can come in a variety of forms, both natural and man-made, but they have one thing in common - they produce a false or incorrect reading on the radar unit's display. Common sources of electromagnetic interference include airport radar; microwave transmissions; transmissions of CB, ham, VHF/UHF, and cellular two-way radio/ telephones, including police and business radios; faulty sparkplug wires; mercury vapor and neon lights; high-tension powerlines; and high voltage power substations. The radio energy from these sources can overload or confuse the sensitive circuits in a radar gun

    2. Mechanical Interference is any moving object, other than the target vehicle, that can produce a false or incorrect radar reading. The most common sources are vibrating or rotating signs near the roadway; fan blades moving inside or outside the patrol car (air conditioner, heater, defroster or engine fan); another moving vehicle that reflects radar waves better than the target vehicle; and multiple targets in the main radar beam causing multiple reflections of nearly equal strength and making the display read, high, low, or completely blank.

    3. Multi-Path Beam Cancellation occurs when the radar signal returning directly to the radar gun from the target vehicle is canceled by a secondary reflected signal. This cancellation can occur while the target remains in plain view of the operator. The display may blank or suddenly switch to another vehicle beside or behind the original target until the cancellation ceases.

    4. Panning occurs when the radar beam accidentally sweeps past the counting/computing unit. This can happen only to a two-piece radar unit. The radio energy from the antenna portion overloads or confuses the counting/computing circuitry.

    5. Shadowing is a problem that occurs only with moving radar, and plagues all moving radar. The radar locks onto a large moving object in front of the patrol car instead of the passing terrain and computes the difference in speeds between the two vehicles as lower than the actual patrol speed. Consequently , the radar adds the remainder of the patrol speed to the target's speed, producing an erroneously high reading.


    6. Batching is caused by time lags in the computing of speeds by some types of moving radar. If the patrol car rapidly accelerates or decelerates while measuring target speeds, the display can read higher or lower than the actual speed.

    7. Stationary Cosine Error is a problem which occurs when the radar unit is not taking its readings from vehicles that are directly ahead of or behind the police vehicle - there is an angle between the radar unit and its target , and it is the cosine of this angle (remember your high school trigonometry?) that determines the magnitude of the error. With stationary radar, the greater the angle between the radar and the roadway, the lower the indicated speed. This error does not become significant until the angle to the roadway exceeds 10 degrees. Fortunately, with stationary radar, the cosine error is in favor of the motorist.

    8. Moving Cosine Errors can result in readings that are either higher or lower than the target's actual speed. More often, the erroneous reading is not in the motorist's favor.

    The moving radar can lock onto a large object to the side of the roadway instead of the ground and, due to the cosine error, compute a lower-than-actual speed for the patrol car. The remainder of the patrol speed is added to the target's speed. Similarly, if the radar is not carefully aligned within 10 degrees of the patrol car's direction of travel, it will compute a lower-than-actual patrol speed. Again, the remainder is added to the target speed.

    On the other hand, if moving radar is used to measure across a wide median, as on an interstate highway, the large angle can cause a lower-than-actual target speed to be displayed , assuming the patrol speed is correctly computed.

    9. Multiple Bounce Errors sometimes happen when there are multiple moving targets within the main beam, causing several reflected of near-equal strengths but varying frequencies to arrive at the radar gun's antenna. Depending on the gun, the display may switch from one speed reading to another, it may show a combination of the reflections, or it may blank out.



    Overpasses on freeways are commonly the source of multiple bounce errors. The error observed most often is a double bounce which causes the patrol car's speed to be indicated in both the target display and the patrol display. Sometimes the overpass bounce will involve a large, slower-moving vehicle near that patrol car, causing the target speed to be displayed as the speed of the patrol plus that of the slower vehicle.

    In another multiple bounce case, the signal can be reflected more than once, by two moving objects, and the total Doppler shift will be displayed as a higher- than-actual speed.

    10. Terrain Error takes place when hilly or curved roadways affect radar's ability to process information. When the patrol car is at the crest of a hill, it is very easy for radar to overshoot the nearest vehicle and instead take a reading from a vehicle on the next hill. Because traffic radar is "direction blind," differences in reflectivity may cause instant-on readings to display the speed of a receding vehicle rather than of an approaching vehicle. So that vehicle "on the next hill" need not even be traveling the same direction as the supposed target vehicle.

  3. #3
    Join Date
    Jan 2009
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    28

    Default Re: How is Radar Effected by the Police Driving Speed

    I found PDF that simplified it. But yeah if he was in motion and he states that the radar showed him 51 then i was not going 51 because he would have to minus his speed as in the PDF example if a car was moving away from a police car and showed 20MPH and the police was going 50MPH then the actual speed would be 70MPH.

    Now the next thing is will he be honest and state he pinged me almost a block away and while he was moving toward me. Then its's all if teh judge can see the error or ignores it.

  4. #4
    Join Date
    Aug 2006
    Posts
    563

    Default Re: How is Radar Effected by the Police Driving Speed

    HOWEVER...

    Radar Knows What is Coming or Going
    DSR is a revolutionary new police radar that features moving direction sensing technology. This breakthrough technology allows the DSR to know if targets are approaching or going away from the radar - in both stationary and moving modes.

    ALSO
    True Doppler Audio
    The audio tone from conventional radars will vary in pitch when the patrol car's speed changes. The audio in the DSR is compensated for patrol speed, so the pitch always is directly related to the actual target speed. This allows the operator to know target speeds just by hearing the pitch, eliminating the need to constantly watch the display.

    so,,,,
    chances are,.. his unit auto-compensates for this using this "dsr" and gives an accurate reading.

    so you may have some difficulty proving that he read the reading wrong or it malfunctioned

    you might want to find out what model # he used.

    and a lawyer with traffic experience can help with these things.

  5. #5
    Join Date
    Jan 2009
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    28

    Default Re: How is Radar Effected by the Police Driving Speed

    If only I could afford that. Also unlike other police he was still using the handwritten citations where as many have the new electronic im not sure how up to snuff the Tucson PD is on tech.

  6. #6
    Join Date
    Aug 2006
    Posts
    563

    Default Re: How is Radar Effected by the Police Driving Speed

    let us know what they have

  7. #7
    Join Date
    Jan 2009
    Posts
    28

    Default Re: How is Radar Affected by the Police Driving Speed

    im in the process of trying to find out what would be my rights in this I seem to remember that in civil cases I would have not right to discovery????

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