PostHeaderIcon Radar Love: Last Car To Pass, Here I Go


Radar is an acronym for radio detection and ranging. Doppler radar units, like the one…

Wait a minute. Before we continue, I believe this post calls for some serious driving music. So click on the video below, turn up the volume, step on the gas, and hold on!!



There, that’s better. So, as I was saying, Doppler radar units, like the one in the top photo, emit a continuous frequency that bounces off a moving object, such as a car or truck. The radar unit receives the reflected signal and instantly calculates the target vehicle’s speed. Doppler radar units are capable of determining a violator’s speed while the patrol car is motionmoving radar—and, while it’s stationarystationary radar.

In the moving-radar mode, the radar unit has to determine the police car’s speed before it can calculate the speed of a target car. It does this by sending a signal to the surface of the pavement and to the surrounding landscape. The unit picks up the reflected signals and converts them to miles per hour—the police car’s speed. The patrol car’s speed is displayed as patrol speed on the face of the radar unit (see above photo). During this exchange and calculation of information, the unit is also sending a signal to the target vehicle. The reflected signal is transposed into miles per hour—the target vehicle’s speed. The target vehicle’s speed is displayed as target speed on the face of the unit.

In the stationary mode, the radar unit simply subtracts the difference between the frequency it sent and the one it received. The difference is calculated and shown as miles per hour on the target screen. No patrol speed is shown when the unit is in stationary mode because the police car is not in motion.

Radar facts:

1) Police officers are not required to show the radar unit to a speeder.

2) To be certain the radar unit is operating properly, police officers must check and confirm the machine’s calibration before and after each shift. They do this by striking and holding a tuning fork in front of the radar unit’s antenna. Each tuning fork is designed to simulate a pre-determined speed in miles per hour. Two tuning forks are used when calibrating a radar unit—one fork is pre-set to 65 mph and the other simulates 35 mph.

The radar unit picks up the forks vibrations as speed and displays its calculation in the target speed window. If the calculated speed is the same as the speed generated by the tuning fork, the unit is operating properly.

3) Patrol car speedometers must be calibrated for accuracy on a regular basis.

4) Some police cars are equipped with devices that allow officers to swipe a person’s driver’s license like an ATM card. The machine automatically records the driver’s information and then prints out a traffic summons. The device is also capable of transmitting the data back to the police station and to the court.

5) A traffic stop for speeding is an arrest. Signing the ticket is the same as posting a bond. The driver’s signature on the summons is his/her promise to appear in court. A refusal to sign a traffic summons could send you to jail.

6) Police officers receive special training before operating radar units.


Officers use tuning forks to calibrate Doppler radar units. The gray and black device inside the car window is the rear antenna for the radar unit. The front antenna is pictured in the top photograph. It’s the round object to the left of the radar unit.

Note the patrol speed on the unit in the top photo matches the speed on the car’s speedometer.

7 Responses to “Radar Love: Last Car To Pass, Here I Go”

  • Terry Shames says:

    Love the soundtrack to this post! Only time I was ever stopped for speeding was 3AM in Virginia. Luckily, I hadn’t been drinking–but I was going REALLY fast in my new (used) Austin Healey. I was also lucky getting a patrol officer who only gave me a ticket for going 68. Anything over 70 in VA at the time was considered reckless driving. “Thank you very much officer.”

  • Dave Swords says:

    Hi Lee,

    I ran radar for a short while way back when. I enjoyed it, for the most part. I’d get a few movers for the day and then I was free to go on “hot-shot” calls the rest of the shift.

    Anyway, I’ll pick a slight bone with you on point #2. We were always trained that we did not calibrate the radar each day, as that must be done by a qualified technician. Rather, we “checked the calibration” of the radar. A seemingly trivial difference, but one a good defense attorney might jump all over in court.

    Also, Do you have any idea what percentage of departments use the Doppler radar, as opposed to the laser based system?

  • Lee Lofland says:

    Good eyes, Dave, and I made the correction. I knew better and had testified to that point many, many times over the years. A “duh” moment for me.

    I don’t know the numbers of Laser v. Doppler, but I know there were plenty of them using Laser when we made the trip to N.C. during the Thanksgiving holiday.

    I absolutely despised working traffic/running radar.

  • Bud Crawford says:

    Can a moving patrol car get a reading on an approaching vehicle as well as one going the same direction?

  • Lee Lofland says:

    Yes, Bud, but it takes a different kind of unit to detect the speed of a vehicle going in the same direction as the patrol car. Also, I have, as have others, issued a summons for speeding after “pacing” a vehicle. Pacing is simply traveling behind a car at the same speed. Of course, you have to follow for quite a ways to be certain the excessive speed wasn’t merely a fluke – passing a vehicle, going downhill, etc. And, the car driven by the officer must maintain regular calibrations of the speedometer. Which, by the way, must be done for cars used to run radar. But, for me, someone really had to be flying or driving recklessly to get me to write a speeding ticket. Normally, I flashed my blue lights, “burped” the siren, etc., to let the driver know to slow down.

  • Interesting. Only ticket I ever got was doing 44 in a 25 mile zone. I was the last car in line. LOL And Hubby checked my car later and it read lower than I was actually going by 9 MPH. I really did think I was only going 35 but I was following about 8 other cars. Lesson learned.

  • Kris says:

    I got stopped for speeding…well, sort of, a while back when I got a flat tire. Coming down a hill, a rear tire blew and about ten seconds later a State patrol car went by the other way. He did a u-turn, came up behind and flashed his lights at me. Considering I was limping along on the shoulder of the road by that time, I’d have thought he would have seen the obvious but he informed me I’d been going 71 in a 65 mph zone. I started to laugh, as my old beater of a truck could barely get up to the speed limit on a good day. (Maybe with a tailwind and Superman pushing) Maybe my laughing at the idea of a speeding ticket made him reconsider, as he just gave me a verbal warning–and helped me change the tire.

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