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How do tmu dash radars work?

Discussion in 'Politics, Laws, Government & Insurance' started by ajc_082, Jul 14, 2009.

  1. I tried to search, but couldn't find anything. I was wondering if anyone has a link or insight to how the police dash mount radar works, the type that allows them to detect oncoming traffic while moving. I was done by one last weekend, and am intrigued how it works.

  2. They measure your speed and the lovely twat in the front seat gives you a reward for doing so.

    Something about measuring the oncoming speed, subtracting the police speed and coming to a figure that helps you prop up the guvmint bank account.
  3. yeah I thought it might be something like that vic, I just wondered if it measures a stationary object or something as well. Presumably its accuracy would then come down to the police vehicles wheel speed sensor..... which adr is +/- 10%. Unless theirs is spot on.
  4. The mobile radar units are not connected to the vehicles speedo, they take the speed reading from fixed objects. They also read the speed of oncoming vehicles and display both the police speed and target speed. Newer versions can also measure the speed of vehicles traveling the same direction in front of the police car. Accuracy is +/- 2 km/h.
  5. Speed is distance in a given amount of time.

    2 signals hit your vehicle and bounce back, separated by a set amount of time. The time it takes for each signal to return is timed, given the known speed of a radar signal, this gives your distance at 2 different intervals.
    The difference in those distances, considered by the amount of time between the signals gives your speed.

    The speed of the moving police car is then either added or subtracted to your speed, depending on whether or not you are moving towards or away from it.

    In theory...
    Yes, the radar guns, and police speedometers are calculated at such highly regular intervals that they are never incorrect, carry a margin for error, or could be called into question in a court of law.

    In truth...
    Sometimes they are calibrated with an up-to-date certificate, sometimes they aren't. You can request certificates, and they may provide one... or both... or none... or ask for more time... and each instance is a day you have to take off work (-$$$) to play their game.
    Then, as happened to a friend of mine, even when they produce an out of date calibration certificate from the radar gun, the magistrate gave the police plenty of time to go get a new certificate fabricated to bring back into the courtroom after apparently 'finding the right one', conveniently forgetting their are tracked by serial number.
  6. I wonder if they display the speed of the vehicle or just the cash and demerit points? :)
  7. Cheers Bonk..... Yeah that makes sense, I just couldn't work out how it could take a reading whilst moving lol. Yeah, I was asking just purely for curiosity, not disputing being booked...... caught fair and square :oops:

    donuts that could be right, with add-on charge buttons for "no license" or "unroadworthy vehicle" just like a cabcharge meter :LOL:
  8. If you are going to get done, get done in Tassie on the Esk Hwy.

    Had Mr Plod ping me with an on-dash radar.

    127km/h gets dropped down so you only cop 1 point and an $80 fine.

    Gee I love Tassie ;)
  9. and are these radars like the lidars, built for use in open space, away from built-up areas, and susceptible to interference from shiny things?
  10. Thats not fair....... *sob *sob

  11. Was thinking the same thing... :evil:
  12. Sorry, have to disagree here...

    Speed Detection Radar works by Doppler shift, not distance/time measurements. What you're thinking of is Laser.

    Doppler shift is the increase or decrease in frequency of the received signal wrt to the transmitted signal, much like the change in pitch between an approaching and departing train.

    The control unit works out the frequency shift of the returned signal which is proportional to the speed of the object it has been reflected by. By using filters the unit can differentiate between several different signals.

    In the case of the mobile radar it measures the speed of the "background" and that of the target wrt to the police vehicle. By subtracting one from the other it calculates the target speed. It is totally independent of the speedometer though it can be connected to it to assist in resolving low speeds. For anything over say 40 km/h there is no need for the speedo connection at all.
  13. :LOL: :LOL:
  14. Wow ajc, you couldn't have searched very well or too hard... there's a whole website and business devoted to radar detection information and fighting cases based in QLD... first hit on the simplest google search...

    By the way, commiserations on the detection.
  15. ahh ok u got me robsalvv....... didn't search too hard :oops:

    Thanks, but there's no disenchantment this end on the detection........ as stated above caught fair and square. Only too happy to contribute to the Brumby retirement fund.
  16. Those pics of the Vicpol solos are old! They are fitted with the old analogue radios. They dissappeared in 2005!
  17. Damn it, we need ECM! I have a friend who designs radars for military purposes. I wonder if he could design a jammer that couldn't be detected by the po-po? :twisted:
  18. What shits me up the wall the most about it all, going past all the possible reflections off other devices, is, the radar does not show a picture of what it was tracking at the time of the reading.

    It doesn't show if it were tracking a car, bike, bird, plane etc... Worse off, those 'readings' that they 'let you see' if you want to check could be hours old. So all the bullshit c^&* eyed pigs could be meeting their quoter with a reading from a few hours earlier. C%&^s!! :evil:
  19. Then it would be a bit weird that their ticket book would be filled with tickets that had both the same speed checked at the same distance. They would be very accountable and that sort of paper chain would screw them. So it wouldn't happen.