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re: How does a cop's radar on a moving motorcycle work?

Posted on 1/26/23 at 8:48 am to
Posted by Chad504boy
4 posts
Member since Feb 2005
166506 posts
Posted on 1/26/23 at 8:48 am to
quote:

nes2010


thanks, it still didn't answer my specific question of how the radar knows how fast itself is moving to do the subtraction of the speeds.
Posted by Napoleon
Kenna
Member since Dec 2007
69218 posts
Posted on 1/26/23 at 8:51 am to
It's linked to the vehicles OBD2 system. Others have an internal GPS device. While driving the radar computer knows the speed the car It's in is traveling.


The ones you see cops pointing and aiming are laser detectors. In those they have to hit a reflective surface to get a signal. So those usually aren't used when driving.
Posted by NATidefan
Two hours North of Birmingham
Member since Dec 2008
36143 posts
Posted on 1/26/23 at 8:52 am to
quote:

That or GPS, my phone and radar detector both use GPS to determine my vehicle speed, it matches what the speedometer of my car says.


Modern ones probably use GPS.

Older ones probably used the accelerometer reading.
Posted by Chad504boy
4 posts
Member since Feb 2005
166506 posts
Posted on 1/26/23 at 8:54 am to
quote:

It's linked to the vehicles OBD2 system. Others have an internal GPS device. While driving the radar computer knows the speed the car It's in is traveling.


So random local sheriff on a motorbike, you think their radar gun they pull out is physically linked to the motorbike's system?
Posted by Lonnie Utah
Utah!
Member since Jul 2012
24067 posts
Posted on 1/26/23 at 8:56 am to
The radar is constantly measuring it's speed by measuring how fast object around it are moving. When it "locks on" a target that is moving faster or slower than those values it preforms a math calculation to figure out the speed.

Posted by NATidefan
Two hours North of Birmingham
Member since Dec 2008
36143 posts
Posted on 1/26/23 at 8:57 am to
quote:

So random local sheriff on a motorbike, you think their radar gun they pull out is physically linked to the motorbike's system?


That or it has built in GPS.

It's pretty much the only two ways it could know how fast it's going to perform the needed calculation.

You're getting irritated at us, but we have answered your question. Multiple times.

I have a blue tooth obd2 reader. It puts my accelerometer reading on my phone, so it could be done in some way like that too.


We have fricking 200 dollar drones flying around using GPS, you think this is that complicated?
This post was edited on 1/26/23 at 9:03 am
Posted by Chad504boy
4 posts
Member since Feb 2005
166506 posts
Posted on 1/26/23 at 9:00 am to
quote:

You're getting irritated at us, but we have answered your question. Multiple times.



i'm not getting irritated. you insulted my math skills when you didn't know dick nor frick about shite.
Posted by NATidefan
Two hours North of Birmingham
Member since Dec 2008
36143 posts
Posted on 1/26/23 at 9:02 am to
quote:

you didn't know dick nor frick about shite.


Know alot more than you,
Posted by Chad504boy
4 posts
Member since Feb 2005
166506 posts
Posted on 1/26/23 at 9:04 am to
quote:

Know alot more than you,


seriously doubt it.
Posted by Napoleon
Kenna
Member since Dec 2007
69218 posts
Posted on 1/26/23 at 9:05 am to
Hand held gun? No.
Motorcycles unless BMW don't have an on board system.

Could have GPS though.
Posted by Darth_Vader
A galaxy far, far away
Member since Dec 2011
64810 posts
Posted on 1/26/23 at 9:06 am to
quote:

The cop is on th motorbike radaring oncoming vehicle while driving at x speed. How is it possible that an oncoming motorcycle at you is reading an accurate measurement when they themselves are moving at x miles an hour towards an object moving towards them at x mph?


If you’re planning on using this as your defense at the upcoming hearing on your speeding ticket, please do us all a favor and have someone there recording it so we can see the judge’s reaction.

And make sure they don’t hold their phone upright.

TIA.
This post was edited on 1/26/23 at 9:07 am
Posted by GusMcRae
Deep in the heart...
Member since Oct 2008
3244 posts
Posted on 1/26/23 at 10:05 am to
We’re on the verge of creating true AI, place complex machinery in orbit, have developed assassin drone that are controlled from 1,000’s of miles away, and you wonder if we can develop a radar speed detector that can be accurate while moving?
Posted by yaherrdme
The Place to Be
Member since Feb 2004
5446 posts
Posted on 1/26/23 at 10:35 am to
Posted by Warheel
Member since Aug 2011
2065 posts
Posted on 1/26/23 at 10:51 am to
I know that some radars have “stationary” mode and “moving” mode. The cops that are sitting still are in stationary mode (unless ton see them aiming a laser gun, laser guns don’t have a moving mode).

When they are in motion they switch to moving mode. If their radar is on, and there are no oncoming cars, the radar shows the speed of the patrol car (in a window on the radar saying “patrol speed”, as someone mentioned by reading the radar signal coming back off stationary objects. When a car is approaching the radar does the math and a speed shows up in the “target speed” window.

Some radars can check the speed of a car going on the same direction as the patrol car, but you have to put the radar in that mode so the radar can do the math.

It’s all about the Doppler effect.
Posted by KiwiHead
Auckland, NZ
Member since Jul 2014
27733 posts
Posted on 1/26/23 at 11:29 am to
Unless the cops have an advanced version of Synthetic Aperture Radar, I would suspect the radar reading would be less than optimal.
Posted by toosleaux
Stuck in Baton Rouge traffic
Member since Dec 2007
9230 posts
Posted on 1/26/23 at 11:33 am to
I have seen some stupid questions on this website, but this is towards the top.
Posted by geauxjuice
t(-.-t)
Member since Jan 2007
4129 posts
Posted on 1/26/23 at 11:33 am to
quote:

The radar knows how fast the cops motorcycle is going. Then using math it calculates the other vehicle's speed.


as long as we're not trusting the cops to do mental math
This post was edited on 1/26/23 at 11:34 am
Posted by GofishMS
Mississippi
Member since Nov 2020
191 posts
Posted on 1/26/23 at 11:56 am to
When I was working with a communications company, we had to install redar detectors in LE vehicles. The way we calibrated them was with a set of tuning forks which would vibrate at a frequency corresponding to a speed stamped on the fork.
Posted by GruntbyAssociation
Member since Jul 2013
3862 posts
Posted on 1/26/23 at 11:58 am to
It is set to the speed limit of the road on which he is running radar. He has to drive at the speed limit to register accurate reading of the oncoming lanes of traffic.
Posted by RollTide1987
Augusta, GA
Member since Nov 2009
65147 posts
Posted on 1/26/23 at 12:04 pm to
quote:

how?


It's called the doppler shift.

Most radar guns are FMCW (frequency modulated continuous wave) radars which allow the host to detect range as well as velocity.
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