Radar clocking from oncoming cops?

[thelinja]

I was wondering if anyone knows exactly how a police radar gun works. My friend and I who has a black 944 were traveling to an autox this past weekend on a state road where the speed limit was 55 most of the way. He was traveling ahead of me and we were both doing 57-58mph. My pal sees a black oncoming car swerve into our lane, then back into his lane. He then swerves back into our lane and my friends radar goes off. So we keep going and the PO turns around and pulls us over and says we were both going 68mph in a 55. My friend and I both tell him what we were traveling (57-58mph) and we got away with warnings. Now my question is this, wouldn't his radar gun read faster because he is heading towards us? I really don't have any idea how a radar gun works besides that the gun shoots some kind of signal and the speed it reads is based on the time it takes for the signal to return to the gun. Does this just sound like a way to fuck people over that aren't traveling in pairs or groups? Becuase I think the only reason we got off was because we both said we were going around the same speed, which was not what the gun read and 10 times out of 10, a PO isn't going to pull you over for going 2-3mph over the SL. How many other states allow for the PO to clock oncoming traffic while they themselves are moving? I've heard that only a few states allow this, but I'm not sure how accurate my source is.

Discuss.

[Steeles]

yes its legal. most guns the computer can compensate for the car moving. much the same way radar is used in fighter jets. theres math involved. the officer needs to have the calibration checked on his gun and make sure his certificatin to use the device is up to date. (well if you had gotten a ticket, you got a warnign so dont worry about it) but if you try and fight it ask to see the last calibration and the officers last cert update.

[adoboboy]

radar works basically by frequency translation...they emit radio pulses and then measurs the doppler effect. Kinda like how a rice boy in his honda does a ricer fly by w/ his blinkers on...thinking he won the race. The exhaust pitch changes as he goes by. Its high pitched at first, then lower as he does his fly by. the difference in pitch is the doppler effect. in the radar's case, its the change in frequency w/ respect to its source is due to it bouncing off the speeding car...then translated into a speed.

U could always ask him to prove it to u...i believe a little sheet that says your speed gets printed out.

[Andrew Bohan]

right
that didn't answer the question at all...

[Steeles]

yeah just leave the explination at "the computer knows how to correct for the officer's car moving"

[thelinja]

yeah just leave the explination at "the computer knows how to correct for the officer's car moving"
I figured it had to be something along those lines. I just don't understand how his radar gun could've been off by 20%. It's great to know that there are PO running around with inaccurate guns.

[andrave]

they are supposed to certify them every year, and they have to be certified to use them. (thats 2 certificates if you are counting).
But they won't even show you the radar if you call BS. in fact they get real pissed. I think they should HAVE to show you. Cause cops, as a group, are mostly assholes. Why else would they become cops? the great pay, or all the friends you make?
(tongue in cheek)

[kandyflip445]

If you were near a semi it would throw off the reading. I'd say user error/not calibrated though. I have no idea what adobo was thinking when he posted, lol. Who cares about doppler effect.

[TheSnail]

For them not to have a calibraded gun is rare. Unless they are a lazy as pig. All they do ( which they are sopposed to do when they step in the car) is push a claibration button on the detector, pull out a horse-shoe shaped tool, smack it with a metal drum stick, and the radar will give out a reading. If the reading is in spec, they are good to go. I am not talking out of my ass, or jest read what someone wrote on the net, but had to hang out with the police see what they do on the job, for probation reasons.

[nismo2491]

yeah the horshoe thing is a tuning fork and that is what they use to check it. also the guns work on doppler effect, imagine somebody flying by you at 60mph blaring their horn, how it makes that distinct sound, the actual tone coming from the horn didn't change, but the sound pitch you heard did, thats called doppler effect and thats what the guns work off of. so yeah adobo did know what he was talking about. and the reason semi's can throw off the reading is because of their huge coefficient of drag distorting the air around them.
also in response to his first question, in MD and VA they can use rolling radar.
KEvin

[kandyflip445]

A lot of police use laser now though. There is laser A and laser B one measures the speed of large passing objects (trees, roadsigns, anything consistant speed to identify the speed of the vehicle it's in) then it has another bounce off your car which it then compares to the wide beam. Then you have the speed. I don't care about doppler. I never said he was wrong. OMG.

[MakotoS13]

if the gun by chance WAS off, however, the fact that it was moving toward you would probably amplify the incorrect reading due to it needing to A-compensate and B- judge your speed. a 10% error could easily become 20% in that case...

[nismo2491]

I have no idea what adobo was thinking when he posted, lol. Who cares about doppler effect. sure sounds like you were saying he was wrong or whatever. but no reason to argue that point. in my experience with ride-a-longs, and stuff like that they don't use laser while driving, they need to physically aim the laser with either a scope style thing thats on it or some actually have a built in red dot that it puts on the car with a visible laser. most rolling radar is actuall ka or k band radar, usually ka.
Cause cops, as a group, are mostly assholes. Why else would they become cops? the great pay, or all the friends you make?
dude grow the fuck up. I'd love to see this world without cops, that'd be interesting. they are performing a public service and like I said in this thread http://www.zilvia.net/f/showthread.php?t=62144&page=2 they are and should be held to the same respect as military. who are the first people you call when your car gets broken into, you get in a bad accident, that type of shit, who's the first on the scene. 9 times out of 10 the cops are there and making sure everything is safe and there are no major injuries before any paramedics arrive. there's a lot more I can say on that subject but since I typed it basically 10 minutes ago go look at my post in the other thread.
KEvin