Radar setup angles

[StoneChucker]

Just incase you thought I was serious, I can't even wheelie!
But I can understand what you're saying. I heard somewhere (so it MUST be true ) that police have to give up the chase at like 130/140km/h? And if someone flies past you at anything faster than that, you're not going to catch him period. BUT... You have little boxes in your car don't ya, like talking boxes linked to other cars? Sheesh, it's to hi-tech for me , but you can't outrun the radio as everyone says...

PS: At those speeds you MAY just catch up to him(*edit* or her*), wrapped around a pole

[thehollowmen]

I'm searching around
Sciam had a nice article about radars and angles... how the radar worked..

Though from memory you're right, it does work to the approaching car's advantage to be at an angle...

edit - this article
http://www.sciamdigital.com/browse.c...B39&sc=I100322

sure I've got it in a mag ... I'll scan if you want

[thehollowmen]

right... looked through the shelf and that one is missing
but I did find this website:
http://copradar.com/preview/chapt1/ch1d1.html

"The angle between the (microwave or laser) radar and target (alpha in the figure below) must be small for the radar to accurately measure speed. The angle is referred to as the Cosine Effect angle because measured speed is directly proportional to the cosine of this angle; the larger the angle the lower the measured speed"

I think this means if you're 10 lanes over and at a close to 90 degrees from the cop you will be pretty much safe :-P

they have lots of neat chapters on this... the 'cosign defence' and other things:
http://copradar.com/preview/chapt7/ch7d2.html#ceffect
http://copradar.com/preview/chapt4/ch4d1.html

hope this clears up a few questions

[scumdog]

right... looked through the shelf and that one is missing
but I did find this website:
http://copradar.com/preview/chapt1/ch1d1.html

"The angle between the (microwave or laser) radar and target (alpha in the figure below) must be small for the radar to accurately measure speed. The angle is referred to as the Cosine Effect angle because measured speed is directly proportional to the cosine of this angle; the larger the angle the lower the measured speed"

I think this means if you're 10 lanes over and at a close to 90 degrees from the cop you will be pretty much safe :-P

they have lots of neat chapters on this... the 'cosign defence' and other things:
http://copradar.com/preview/chapt7/ch7d2.html#ceffect
http://copradar.com/preview/chapt4/ch4d1.html

hope this clears up a few questions

AND if you're not exceeding the speed limit you are even safer!!

[TwoSeven]

From my understanding of radar, I dont think there are any angles involved. Signal goes out, hits object returns. Also does not radar travel at a fairly good speed - compared to that - the car would be pretty stationary wouldnt it.

[thehollowmen]

From my understanding of radar, I dont think there are any angles involved. Signal goes out, hits object returns. Also does not radar travel at a fairly good speed - compared to that - the car would be pretty stationary wouldnt it.

yes, but this is saying the radar measures the speed of the object directally in frount of it as though it was moving directally towards the radar... it can't measure side to side movement unless it has some form of reference object...

If I walk towards you at a pace every second, you'll see me walk at a pace per second towards you...

now if I walk at 45 degrees to that... at a pace per second... it will look like I'm moving slower directally towards you (about 70% of the speed I was moving towards you at before) , but I'm still moving at a pace per second...

[thehollowmen]

AND if you're not exceeding the speed limit you are even safer!!

Oh I so agree with you there


me? speed?
my bike doesn't even go that fast

now can anybody change a rear sproket for me to make me go faster?

[scumdog]

From my understanding of radar, I dont think there are any angles involved. Signal goes out, hits object returns. Also does not radar travel at a fairly good speed - compared to that - the car would be pretty stationary wouldnt it.

Eh? think of it this way ( you're not trolling are you?), a car is going from left to right at a 150kph, it is approaching at a 15 degree angle, the radar only measures at the CLOSING speed of said car, (i.e. straight towards the radar) hence the car only shows a speed of 25 kph.

[Mr Skid]

Just incase you thought I was serious, I can't even wheelie!

You can't wheelie an R1? :spudwhat:

[badlieutenant]

Signal goes out, hits object returns. Also does not radar travel at a fairly good speed - compared to that - the car would be pretty stationary wouldnt it.

speed of light ? electromagnetic frequencies ?yer, and yer right, relative to the radar the object would apear to be stationary but I think it measures the rate of change of said signal to travel there and back each time, assuming its from the same object each time. or your just taking the piss.................

[scumdog]

speed of light ? electromagnetic frequencies ?yer, and yer right, relative to the radar the object would apear to be stationary but I think it measures the rate of change of said signal to travel there and back each time, assuming its from the same object each time. or your just taking the piss.................

At the risk of being trolled: Imagine you are God looking down on an airport and a bike is going from left to right on one side of the runway at 100kph at an angle approaching you of say 20 degrees, you are standing on the other side of the runway which is 100 meters wide.
The bike is doing 100kph, no question, it is crossing the runway towards you at a shallow angle taking 5 seconds to cross the runway. That means its approach speed in a straight line from you to it is 75kph.

i,e it is closing the gap to you at 75kph but because it is not coming directly at you it can be doing 100kph ground speed as it goes from left to right.

[badlieutenant]

God ! god! oooeeeerrr risky mate...........
simple pimple really, the shortest distance is a direct line from observer to object, so if object say has a set speed any variation off of the shortest path (straight towards the observer) will be measured as less that the constant speed the object actually is travelling at there, i think Lou understands now.
or am I trolling? lol
you guys should get together and smoke a fat could film it for prosperity when one of you becomes the others boss.......
bring back the MOT and thier really kewl pants (dont know why they got refered to as nazis?)


*im changing my alias and moving to the hills*

[Lou Girardin]

isn't that what i said?

get a couple of matchbox cars out lou, and do the math in visual symphony, as obviously your tiny brain can't compute it without external input. if the vehicle being tracked (that's you) is travelling at an angle to the vehicle doing the tracking (that's the police - they're the ones in the patrol cars - can you say patrol?), then the cosine angle is advantageous to the vehicle being tracked. there is no circumstance when the radar will read HIGHER due to the angle, regardless if the patrol car is on a corner or on a straight.

Read it again, Marty. Then study traffic radar technology.
If the patrol car is closing the angle to the target the radar reads HIGHER. This is cosine ERROR, a litle different to cosine ANGLE.
A simple arrangement that has got a lot of Americans, where their lawyers understand these things, off a lot of tickets.

[James Deuce]

The only bikers I've ever chased are the types that stink real bad and wear patches on their backs. I've heard it heaps of times over the radio where a cop calls up to say that he just clocked a bike at 240'ish. Ask for a description....."I think it was a red one"! Roger, we'll keep an eye out for a red bike.

If you went past me like that I'd be saying, "There aint no way I'm going to catch that guy so I might as well enjoy the show".

PMPL!! On both counts.

[TwoSeven]

I get what you guys are getting at - am I right in your talking about the hand held radar guns and the copper being on the side of the road.

Because the fixed point radar is aimed at the front/rear of the car and samples over a short period of time (you'd never have one set up to be more than 15 deg out). It just uses the time the signal takes to come back from the first sample with regards to the second sample - then works out the speed of the vehicle. The distance the vehicle needs to travel is very small, maybe about 10 centimetres or even less depending on the system.

The other kind is just a laser pointer that has a 1k range. And the final system is SPECs which takes a digital photo and does number plate recognition as well. Its very very accurate and usually operated in pairs (so it takes your average speed between points).

Its not the radar/laser thats the problem - its taking the photo that matches the vehicle to the data thats the issue (not sure if NZ requires photo evidence).

I worked with some folks a decade ago that were developing a system for use in UK jam jars. Basically think military grade stuff and I suspect its been well and truly improved by now.