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Characteristics of traffic radar

Discussion in 'Electronic Design' started by Paul Hovnanian P.E., Feb 10, 2007.

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  1. Possible, but you also need multiple receivers, and it does not fix the trick
    of speeding and then parking and having a cup of coffee to have exit time
    - enter time of a road so average speed is < max allowed.
     
  2. linnix

    linnix Guest


    Why not? In response to a request, the car transmits the position
    every second and the receiver cop can calculate it's speed. The key
    to this is a low cost precision gps receiver (accurate to cm). The
    heart of this precision receiver is a stable Cesium clock. Sponser my
    project and I will show that it can work.
     
  3. Yes that would work, using GPS,
    but in my system the receivers are placed at every road, connected to a
    central computer.
    If you speed, you will be charged automatically every time.
    No cops needed, other then coming to pick you up when your account reaches zero.
    I am a bit reluctant to sponsor any of those systems.... freedom and ideas
    like that.
    Gov is starting to invade in a bad way all over the world.
    In Germany now they want to give police the ability to search your PC online
    (without your consent, so hacking it)...
    Do you trust the police down the road with your banking password?
    Where does it end? Brain implant at birth?
    Oops, should not have mentioned that.
     
  4. linnix

    linnix Guest

    Mine too. I just said receiver cop, which could be stationary unmaned
    receiver. We want to take the human factor out of traffic control.
    Our project is to build a precision GPS. How we use it is a different
    story. It could be used as automatic cars or automatic bomb disposal
    unit, but terrorist can also use it as car bomb. Knowing the risks
    and benefits, it would not stop us from developing it. If anything,
    we need better plannings and controls. Initially, the units are
    tagged and controlled via the internet. It's a requirement to give
    up your privacy to use such equipment.
     
  5. I am surprised nobody noticed how fair this system is.
    It favors the rich 100% :)

    eh... you can only do that if you sort of assume the 'system is perfect'.
    As the sytem is not perfect, it is better to keep some playing space.
     
  6. linnix

    linnix Guest

    It may not be prefect, but an improvement. The technology is already
    there. The current system use a encrypted P-code, which is available
    to government agents only (but spies as well). Our proposed system
    use a stable clock source and remote processings via the internet.
    The processing server can turn it off around sensitive area.
     
  7. My question wasn't about how to build one. It was to get some insight on
    existing designs and their tradeoffs.
     
  8. That's a non-technical summary of the subject as far as it goes. Most of
    the interesting subjects are greyed out (no links to actual data).
     
  9. Barry Lennox

    Barry Lennox Guest

    IME, it's hard to get the info, I used to know a tech working on them
    years ago, and he was bound by all manner of confidentiality.

    Another suggestion may be to purchase a used one, there's adverts
    around for them, and measure the characteristics.

    Where is the investigation headed? Purely academic, or with an eye to
    a countermeasures system?

    Barry
     
  10. Academic at this point. I wouldn't try to build any sort of jammer, but
    understanding their shortcomings might prove useful in getting speeding
    tickets thrown out.

    They recently installed one of those traffic signs in my neighborhood
    with the "Your speed is ...". It amazes me at how far off the mark those
    things are under anything but ideal conditions (two or more targets for
    example).
     
  11. Fred Bloggs

    Fred Bloggs Guest

    It's good enough for your purposes. There are tens of thousands of
    architectures for Doppler radar, but you are interested only in traffic
    radar, and within that category, you are only interested in speed radar.
    There is no requirement for coherence or even range determination there.
    I would expect the simplest radar has no LO and does simple digital
    oversampling of the audio difference frequency, allowing full digital
    adjustment of the cutoff frequency high pass filter, set by the operator
    in accordance with the speed limit excess to be ticketed. I would expect
    that the FFT is amplitude qualified for maximum range and reports the
    maximum speed within that window. It is up to the operator to eyeball
    the scene and make the determination of the violator in the event of
    multiple targets. Those crummy little roadside signs are turned way down
    with a range of only about 50m on an average sedan and report the
    maximum measured speed within their window, look to have an update rate
    of about 2Hz. I doubt any of these systems "count" anything and there
    can't be much dynamic range required for head-on RCS variation, I would
    expect less than 6dB. If you need everything explained to you, maybe
    it's over your head.
     
  12. YD

    YD Guest

    Late at night, by candle light, Jan Panteltje
    In Brazil someone came up with the idea of mandatory RFID tags in
    cars. Ostensibly for locating stolen vehicles and automatic charging
    in toll booths, but it's easy to see the real purpose, especially with
    a cash-starved gov't with one of the world's highest tax rates and
    least return. Just place a couple of receivers on poles a kilometer
    apart talking to each other and time every car passing. A real cash
    cow. Nothing will come of it, though. Vehicles more than 20 years old
    are exempt from road tax, mine is 30.

    - YD.
     
  13. The local oscillator is the transmitted carrier. The I.F. is equal to
    the Doppler shift of the reflected signal.
    Doubtful. If the 'setpoint' was 20 MPH and that adjusted the high pass
    rolloff, then one could evade detection by driving sufficiently fast.

    They appear to have more capability than the handheld units. One feature
    of even the cheapo sign units is that they can discriminate between a
    single vehicle approaching or traveling away from the detector. If one
    approaches the sign from the rear, passes it and then looks at it in the
    rearview mirror, there is no speed displayed. This is not a capability
    of most handheld units.

    OTOH, multiple targets cause them to flip between clearly inaccurate
    readings (from 20 MPH to 50 MPH instantaneously).
    That's probably correct. Although range determination would be
    relatively easy to add with a freq. modulated carrier and some DSP
    brains, the units don't appear to have any way to utilize this data,
    even to inhibit possible interference due to multiple targets.

    Oddly enough, there are radar detectors that can count the number of
    emitters found.
    Do you know that or are you just guessing?

    Hint: Moving radar (which calculates both the police car speed and the
    target's difference speed) discriminates between the two based on the
    amplitude of the two Doppler signals. If the detector had this sort of
    limitation, the difference in amplitude due to frequency response could
    easily exceed 6 dB.
     
  14. Rich Grise

    Rich Grise Guest

    When I was in the USAF, I had friends in the "Doppler Radar" department;
    one of their components was "the audio amplifier".

    Ever since I saw that, I've been wondering what it could possibly
    sound like! ;-)

    Cheers!
    Rich
     
  15. For traffic radar, it makes a whistling noise. Most CW* radar guns have
    an audio output so the officer can monitor the signal. An experienced
    operator can detect interference and judge target size and distance by
    the volume.

    *An interesting side note: Many years ago, I got a speeding ticket,
    which I didn't think I deserved. Since I had a radar detector, I knew
    when the officer pulled the trigger on the gun. It was a pulsed unit,
    judging by the short duration of the detector alert. When I took it to
    court, the officer read the usual BS about the radar unit model number,
    that it was a pulsed unit, that it was calibrated within X hours using a
    calibration tuning fork and that the officer had heard a continuous
    Doppler tone and verified that there was no interference. On this last
    bit, I asked how it was possible to judge interference by listening to a
    short tone burst. He replied that the gun puts out a continuous tone,
    regardless of the radar pulse length. I'm thinking that most pulsed guns
    with speaker outputs synthesize the tone based on the speed reading and
    it no longer has any correlation to the actual Doppler signal. Its just
    there to make the cops happy. Or, the cop lied. In any case, since this
    sort of reasoning is way over the heads of most judges, I got that
    ticket.
     
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