On a sunny day (11 Feb 2007 10:17:31 -0800) it happened "linnix" wrote in :
transmitter,
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.
transmitter,
in
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.
On a sunny day (11 Feb 2007 10:40:29 -0800) it happened "linnix" wrote in :
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.
Mine too. I just said receiver cop, which could be stationary unmaned receiver. We want to take the human factor out of traffic control.
zero.
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.
On a sunny day (11 Feb 2007 11:06:36 -0800) it happened "linnix" wrote in :
zero.
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.
zero.
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.
[snip]
My question wasn't about how to build one. It was to get some insight on existing designs and their tradeoffs.
-- Paul Hovnanian mailto: snipped-for-privacy@Hovnanian.com
------------------------------------------------------------------ Karate is a form of martial arts in which people who have had years and years of training can, using only their hands and feet, make some of the worst movies in the history of the world. -- Dave Barry
[snip]
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).
-- Paul Hovnanian mailto:Paul@Hovnanian.com ------------------------------------------------------------------ A mathematician is a machine for converting coffee into theorems.
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
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).
-- Paul Hovnanian mailto:Paul@Hovnanian.com ------------------------------------------------------------------ Dyslexics have more fnu.
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.
Late at night, by candle light, Jan Panteltje penned this immortal opus:
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.
-- Remove HAT if replying by mail.
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.
-- Paul Hovnanian mailto:Paul@Hovnanian.com ------------------------------------------------------------------ Sleep is for wimps. Happy, healthy, well-rested wimps, but wimps nonetheless.
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
[snip]
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.-- Paul Hovnanian mailto:Paul@Hovnanian.com ------------------------------------------------------------------ It is not enough to succeed. Others must fail. -- Gore Vidal
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