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PostPosted: Wed Feb 23, 2005 9:08 pm 
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I believe it is illegal for a speedo to read slow. Having said that if you don't speed you have no problems, we may not like the fact but it is a truism that cannot be argued against. I speed every time I drive and accept that if I get caught I pay the price. The driver of the car is responsible at all times and things are getting tougher. A work colleague of mine is on charges for killing three people in an accident involving his truck and a car. The next thing to accept is that there is no such thing as an accident, they all have a history and a cause. This little fact escapes nearly everyone. I predict that all urban speed limits in Sydney will be lowered to 50kph on all but major roads before the next election. Enjoy.

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PostPosted: Wed Feb 23, 2005 9:44 pm 
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ADR's require that speedometer's read within 10% of actual. I believe this is bullshit in this day and age it should be +/-5%.

Victoria has publicly stated that they have a "Zero Tolerance" Policy for speeding. 60 means 60. If yer over, then you'll be booked. The fact that their speed camera's have been shown to be faulty on quite a few occasions means absolutely nothing.


Nowwwwwww, if ya wanna beat a speed camera fine, or even a speeding fine from a handheld radar device ya might wanna read up on a subject called "Method of Edge Waves In The Physical Theory of Diffraction" by a russian gentleman named Pyotr Ufimtsev.

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PostPosted: Thu Feb 24, 2005 9:31 am 
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christ phildo... just give us a damn summary ... ;)

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PostPosted: Thu Feb 24, 2005 8:24 pm 
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LMAO, he goes on to explain the effect of radar against objects of different shapes and sizes.

The F-117A stealth fighter was designed using the principles Ufimtsev had researched. Using shapes and sizes would diffract or reflect(redirect) the radar in a direction other than the sender. Which is why the plane is made up of so many angles and such. Now if you consider that vehicles are made up of many different shapes and sizes,you may be able to convince a court that there is no possible way that the police can prove the speed they believe you were doing. There are a zillion other factors that need to be taken into account, including the direction the vehicle is travelling, if it is turning(doppler shift), or if another vehicle (or radar reflecting object) is nearby, which could cause random backscatter to be recognised as a signal and render a false indication on the radar device. I'm no expert in the matter, that's why I mentioned looking at Pyotr's study.

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 Post subject: Radar Puke...
PostPosted: Thu Feb 24, 2005 8:45 pm 
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PhildoD wrote:
LMAO, he goes on to explain the effect of radar against objects of different shapes and sizes.

The F-117A stealth fighter was designed using the principles Ufimtsev had researched. Using shapes and sizes would diffract or reflect(redirect) the radar in a direction other than the sender. Which is why the plane is made up of so many angles and such. Now if you consider that vehicles are made up of many different shapes and sizes,you may be able to convince a court that there is no possible way that the police can prove the speed they believe you were doing. There are a zillion other factors that need to be taken into account, including the direction the vehicle is travelling, if it is turning(doppler shift), or if another vehicle (or radar reflecting object) is nearby, which could cause random backscatter to be recognised as a signal and render a false indication on the radar device. I'm no expert in the matter, that's why I mentioned looking at Pyotr's study.


All good stuff PhildoD...however....a lot of "radar guns" are now lasers...much more directional, way shorter wavelengths..more accurate.... gotcha :!: (if you have a descent frontal area...wedge shaped Hondas need not apply)

BUT...if the average nerd in the street DOES NOT have the means to tell how accurate his speedo is on a regular basis ...then it is morally wrong to talk about ZERO TOLERANCE!! If police are going to use these tactics in the name of SAFETY (see I didn't mention revenue raising :wink: ) then they should also be supplying lots of places to check your speed!!!!! Its no good saying calibrate you speedo once a week either because their accuracy relies on other factors such as tyre profile and inflation pressures. How about some large readouts like they have on the Waterfall Expressway (well they did have a long long time ago!)

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PostPosted: Thu Feb 24, 2005 9:06 pm 
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the radars that the police use are continuous wave doppler radars. They rely on very small shifts in the frequency of the returned signal, which is an indication of the speed of the object that is being illuminated by the transmitted signal. Your theory on trying to blame other vehicles, or backscatter from other objects in region falls down because the antenna design of the radars is such that it focuses the beam fairly well. The sighting of the target vehicle with a handheld radar in the "crosshairs" means that is what is being illuminated. The range at which the radars operates means that the return is still quite a strong signal compared to the background noise, so there is little chance of the radar mistaking a telegraph pole return for that of your car.

i don't know about the "slant" radars they use with the speed cameras though. Most of the fixed cameras are now triggered by conducting loops embedded in the road a short distance apart. And most of the hand helds are lasers now, more because it is safer to point a laser at your testlicles than a radar. at least if ever want to have sons :D

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 Post subject: Re: Radar Puke...
PostPosted: Sat Feb 26, 2005 12:45 pm 
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9YaTaH wrote:
All good stuff PhildoD...however....a lot of "radar guns" are now lasers...much more directional, way shorter wavelengths..more accurate.... gotcha :!: (if you have a descent frontal area...wedge shaped Hondas need not apply)


The only thing laser on the still same radar device is the Laser emitting diode on the aiming reticle(first designed by C-more sights for sidearms). This does give a parallax free aiming medium, but the device still works in the same way. As to pulse doppler radar, changing direction will create a doppler shift other than is expected which WILL give a false reading (commonly used by aircraft). It will not stop a tracking radar but it will prevent the radar from gaining an accurate solution.

EDIT: No matter how focused the beam is, I was personally recorded speeding from a distance of over 400 metres. Not bad for a handheld device!!. I'm doing well to hold a rifle steady lying down at a target 400 metres away. That's bullshit accuracy on a moving target.

I'm not trying to get in a pissing contest, I'm just giving my reasons as to why I distrust the methods used to catch speeding vehicles.

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PostPosted: Sun Feb 27, 2005 10:38 pm 
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yeah, when i said range that they operate in, i meant the design spec, which is probably less than 400m, but the beamwidth is probably still around 10-15deg, which is useless for a rifle aim as you say. the key to this is that wavering hands syndrome will produce frequency changes that are orders of magnitude less than the frequency change due to a vehicle moving above 60km/h. Also the device will have filters tuned to the expected doppler shift. but this is all contingent on them being used within the specified parameters. if you were to try to prove that an error was introduced, you would have to prove that the operator was using it outside the spec.

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