1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Does anybody know the sampling frequency of a cop radar?

  1. Mar 2, 2017 #1
    More specifically, does anybody know the sampling frequency of a mounted 360 degree cop radar? NOT a conical/directional hand-held radar gun.
  2. jcsd
  3. Mar 2, 2017 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    May I ask why you want to know?
  4. Mar 2, 2017 #3
    Yeah sure.
    Its because I got a ticket going 83mph in a 70mph zone, but im POSITIVE that I wasn't going any faster than 72mph at any time.
    What happened was that it was late in the evening and I was in the fast lane when three cars zoomed past me and all quickly veered onto the nearest exit. Just moments after the last car passed and I said "woah" to myself, i noticed a cop car ahead going slow in the middle lane. I immediately looked at my speed and noticed it was just a hair above 72mph so I cooled it to 70mph and eventually caught up to him and passed him going 70 and got pulled over and he said to me "ya know you cant just slow down when you see me and think "oh everythings okay", my radar detects behind me in all directions". I briefly told the officer that i think he might have detected another car that I saw speeding by, but i wasn't going to argue with him. He did make a note of what i said in the ticket though.
    So if the sampling frequency is low enough, I was thinking i could use that argument on my court date
  5. Mar 2, 2017 #4


    User Avatar
    Science Advisor

    You need to know the make and model of the radar.
    You need to get a copy of their instruction manual.
    You need to get a copy of their operational guidelines.
    You need to get a copy of their calibration certificate for that instrument.

    What do you think 360° radar really is ?
    What do you mean by sampling frequency ?
    Is it a doppler radar or a differential distance system like laser speed guns ?

    Note that doppler radar reports the highest speed detected, so on a corner the top of a motorcycle front wheel rim will return a reading about 160% of vehicle speed. As the bike straightens up towards the doppler radar the reading drops to 100%. That is one reason why police think the rider slowed down when they were seen.
  6. Mar 2, 2017 #5


    User Avatar
    Staff Emeritus
    Science Advisor

    I'm sorry but we don't assist with legal issues or matters related to them. Please contact a lawyer and/or other professional who can evaluate this. Besides, how would it feel to arrive in court only to have incorrect information because a few strangers on the internet with the best of intentions were simply wrong?

    Thread locked.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook