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A secondary -but planned!- use for the speed-detecting radar signal?

Discussion in 'Electronic Design' started by Ramon F Herrera, Mar 26, 2007.

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  1. We all know the primary use of a speed-detecting radar signal used by
    law enforcement. The signal is bounced off vehicles in order to
    measure their speed. I believe, however, that here are, a few other
    (intended?, unintended? bug? feature?) by-products of such signals.

    - When I drive near any mall, the signal to detect customers and open
    the store doors automatically triggers a false positive in my radar

    - When an ambulance is running, there is also a detectable signal
    going on.

    - In some toll booths the signal is also present, even though there
    are no cops or anything related nearby (there is no need for the speed-
    measuring aspect).

    Therefore, I speculate that perhaps there is an intended use by the
    radar designers. When the ambulances are running in emergency mode,
    the signal is a way to tell drivers to move away, to slow down, etc.
    BUT (and this is the key issue) the ambulance has no way to detect the
    speed of anybody. Some friends of mine claim -with no evidence
    whatsoever- that ambulances have a signal to turn on green lights
    along their route and this signal "happens" (just by sheer
    coincidence) to be in the same band as the speed-detecting radar

    Frankly, I find that very hard to believe. The mall door are perhaps a
    coincidence (are they, really?), but the design of a remote street
    light changer (with all the dangers that an unexpected asynchronous
    light change implies) which by error just happens to be the same
    frequency!? Come on!

    I claim that the whole thing is planned: I remember reading in the
    Boston news that a guy fell asleep and crashed into a toll booth,
    killing the attendant. Don't know the details, but such sad accidents
    could be prevented by having a radar detector triggering (NOT
    measuring I insist) to turn on the beeper in the sleeping guys' car.

    Any comments, informed guesses?


    ps: which ones would be some pertinent NGs to post this?
  2. Wouldn't a simpler explaination be that its an unlicensed spectrum which
    is well suited to use for radar?

    Door sensors use radar to detect people, I don't know about ambulances but
    I can think of a couple of reasons they might want to be able to detect
    obsticals, at the airport near here we have little cameras setup to record
    number plates as cars are leaving, your toll booths could have a similar
    system in place connected to a motion sensor.

    I can't see the benefit of installing hundreds of thousands of dollars
    worth of radar gear just for the benefit of the minority who have radar
    detectors. Especially when the people with the radar detectors obviously
    haven't been told about it so their first instinct is to look for cameras
    drawing attention away from ambulances, toll booths, etc.

    -- Michael Heydon
  3. Rich Grise

    Rich Grise Guest


    That's done with a strobe light, that flashes at a certain rate. Radar
    has nothing to do with it.

  4. Sorry, but the gizmos that turn the lights green for emergency
    vehicles are OPTICAL, not RADIO. The firetrucks have what amounts to a
    strobe light mounted on their roofs; it pulses light in a specific
    pattern, and a photodetector mounted on the light pole overrides the
    signal and turns it green in the direction of the strobe light.

    None of it has anything whtsoever to do with RADAR.

  5. I should have explained (I thought it was obvious) that when a nearby
    ambulance is in emergency mode, my radar detector goes crazy. As the
    ambulance goes away, the beeping of my RD slows down.

    I find rather doubtful that my RD has an optical strobe light
    detector. When it boots up, it clearly displays: X-Band, K-Band and
    Laser. All 3 are electromagnetic radiations, but they are very far
    from the strobe used by ambulances and the infrared used by street
    light preempting devices.

    A reader in another newsgroup confirmed my suspicion: the emergency
    vehicles indeed carry a low level radar transmitter *only* whose
    specific purpose is to turn on your RD, and cannot measure (or care)
    about your speed. It is the high tech way of saying "out of my way!".
    That device is cheap enough, specially when balanced against human
    lives and property they save, Michael Heydon.


  6. Now I understand your point. Are you saying that what is detected is
    the low frequency (as it can be counted by a human being) rate, as
    opposed to a certain modulated frequency, like the ones used to
    distinguish a VCR remote control from a TV remote control?

    What about day vs. night, obstacles, fog, etc?

    If I can afford a *precise* infrared remote control made by Sony
    ($9.95 at Radio Shack) the police and fire departments in a life
    critical jobs, certainly can.


  7. Aha! My suspicions were correct. The strobe-light detector seemed too
    crude, susceptible to errors, easy to counterfeit. Plus, you want the
    street-light preempting functionality to be independent of the strobe,
    visible light.

    I got this from another NG (sometimes it pays to cross post):



    Well, traffic engineers know quite a bit about radar, its attendant
    transportation and non-transportation uses, and emergency vehicle
    pre-emption (EVP).

    Modern EVP systems use an encrypted signal sent via a modulated 14.035
    Hz wave. If it seems low frequency, it is. Most systems send the
    signal out whenever the front strobe lights of the vehicle are
    flashing (and it is obviously invisible, with visible light being
    several orders of magnitude higher in frequency).

    You'll occasionally see peace officers detaining a motorist, the whole
    time leaving their forward strobes activated and tying up traffic in
    all directions but their own (which is usually already tied up behind
    them). I had a conversation with the Cook County Sheriff's Department
    one morning a few years ago after they repeatedly destroyed the
    operation of a busy suburban intersection over several days. They
    would pull over speeding motorists and direct them onto a side street
    for an entertainment venue that had zero traffic in the AM peak. The
    motorist and the sheriffs patrol vehicle would end up facing back out.
    Because of the EVP call, the traffic signal was held in green for the
    EVP max-out (about two minutes), then recalled immediately after
    returning to serve the other movements. This left the main arterials
    (the cross road and the oncoming arterial) with about six seconds of
    green per cycle - and no arrows for the left turns, either, since the
    detector loops "tuned out" after a few of those incidents and were not
    vacated to "reset" until after the AM peak had diminished.

    Obviously, the only real "fix" for a problem like this, from a traffic
    signal control standpoint, is to not serve an incoming EVP call until
    the previous call is terminated, if the call is from the same unit.

    This requires that the EVP module recognize the difference between a
    fire truck and an ambulance, so that vehicles in a procession but
    separated are not denied calls on the basis of the passage of a
    previous vehicle. There are pitfalls to this practice (all units must
    have unique ID's), but it's probably easier than asking the cops to
    turn off their forward strobes (although some agencies are very good
    about strobe light and traffic advisor management, most are ignorant
    of good practices).

    Scott O. Kuznicki, P.E.
    Civil (Traffic) Engineer
    Dedicated Highway Enthusiast
    Driving Enthusiast:
    '03 525i 5-speed
    '90 Ninja 250R (cheap fun!)
  8. GPG

    GPG Guest

    RF used to detect tags on goods.
  9. Guest

    X band radar is on a "license free" allocation near 10.5 ghz. Door
    openers, microwave car detectors, are in a "license free" allocation
    at 10.5 ghz. A while back it was decided to add a signaling protocol
    to some radar detectors for emergencies and certain roadway warning
    signs at you guessed it, 10.5 ghz.

    Does that answer your observation questions?

    Steve Roberts
  10. Um, no.

    Automatic door openers triggering radar detectors predate RFID by many
  11. Jim Thompson

    Jim Thompson Guest

    RFID tags are typically in the 1-2GHz range... but there are some as
    low as 130KHz ;-)

    ...Jim Thompson
  12. Rich Grise

    Rich Grise Guest

    That could be, as an attention-getting device - after all, when your
    radar detector sounds, you wake up and get back to the task of driving
    the car responsibly, right?

    So I can see that it's marginally feasible, but whatever radar jammer
    they're running doesn't have anything to do with changing the signals.

  13. Rich Grise

    Rich Grise Guest

    It's a strobe with a flash rate of 14.035 flashes per second.

    And if they catch you using one, they'll throw you in the clink.

    Good Luck!
  14. Thanks for your answers, Steve. Let me see if I understood you
    correctly. You say that a signaling protocol was added with the
    specific use of sending a "this is an emergency, get out of the way"
    signal to properly equipped RDs. If that's the case, shouldn't the
    display show something like "emergency vehicle coming"? I really have
    bumped into many ambulances in emergency mode, but IIRC the display
    and beeping sound is the same than for a regular police patrol car.

  15. Guest

  16. RG

    RG Guest

    Google a little, Google a lot. Type "radar detector" and read the result.

    Results 1 - 20 of about 1,050,000 English and Spanish pages for radar
    detector. (0.13 seconds)

    Ever heard of:

    Safety Alert®????

    You have a radar detector, read the instructions..

    From the Cobra XRS-9300 model:

    The XRS-9300 features 2 safety alert systems The Strobe Alert, a Cobra
    exclusive, works with tens of thousands of emergency vehicles currently
    equipped with traffic light controlling strobe emitters and the Safety Alert
    warns driver of emergency vehicles and road hazards from systems equipped
    with Safety Alert transmitters.

    Ahhh, the power of Google.

    Sorry to be a "smart ass"...


    Raul G
  17. RG

    RG Guest

    Following my previous post a little bit more:
    Since many motor vehicles are so soundproof that drivers often do not hear a
    train or siren approaching or see warning lights immediately, Cobra offers
    the Safety Alert(R) Traffic Warning system to help prevent possible
    accidents. When the XT-1000 Transmitter is installed on a train or such
    emergency vehicle as a police car or ambulance, it transmits special warning
    signals that can be detected up to one mile away by Traffic Warning
    Detectors. Detectors, installed in motor vehicles, warn drivers of upcoming
    hazards with one of three alerts: train (at an unguarded crossing),
    emergency vehicle, and road hazard.

    And I don't work for Cobra.. Ha.

    Raul G
  18. joseph2k

    joseph2k Guest

    Sounds like you have a crappy detector, responding to "out-of-band" signals
    like that. Field disturbance detector.
    Same problem, telemetry this time.
    More out of band response, DSRC toll interrogators.
    Yes they have, and it is optical, not microwave. Would you like a link to
    the specifications?
    See responses above.
    alt.religion maybe?
  19. joseph2k

    joseph2k Guest

    Offhand i would say that there are some possibly seriously wrong assertions

    1. In most jurisdictions law enforcement is not allowed to use preemption
    just to pull over someone for a traffic violation. Certainly not in

    2. The red and blue strobes are not at the right frequency.

    3. What encrypted signal? Peruse the device specifications. Want a link?
    It is an MSWord file

    Joseph Barrett, P.E.
    California Department of Transportation
    Transportation Electrical Engineer
  20. joseph2k

    joseph2k Guest

    It is not in use in California that i know of, and I am in a position likely
    to know. Perhaps they are working with the local big city, Atlanta.
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