While all of these Doppler based radar systems use microwave emissions to perform their specific tasks, their designs are quite different.

Standard Police Radar Guns project a microwave beam in one direction only. There is no movement made by the antenna, and no cathode ray tube to display the information that the radargun “sees.” The only information you can get from a Traffic Radar Gun is how fast, and sometimes which direction. None of the police radars will tell you exactly which vehicle is traveling at the speed displayed on the unit.

Aircraft and weather radars rotate 360 degrees on their mounts sending out pulse patterns of microwaves. The signal retuned to the antenna can process the data from this signal to form not only a 2 or 3 dimensional picture of the object, but also determine the speed and direction in which the object is moving. This data is sent to a CRT monitor to display the picture that the Doppler Radar receives. This is useful to see cloud and weather patterns for the forecast. For aviation, it allows pilots and ground crews to know how many planes are in the air, exactly where they are, where they are going, and how fast they are moving. These radar units are very powerful, large, and extremely expensive. While they would be extremely useful to law enforcement, they would be detectable from great distances, and would be over the budget for most police departments.

Ryan

In order to answer this question the first thing I had to do was see how small an object a radar gun could pick up. Since most chronographs are used for shooting sports and archery, I chose a subject roughly the size of the projectile from a 45 ACP cartridge. I chose this caliber, because it is a large projectile for handguns and it travels at a relatively low speed. In this case, I just happened to have a bag of Lemonheads sitting on the desk next to me. Explaining to the owner of the Lemonheads what I intended to do, he gratefully agreed to chuck the Lemonheads at me as I attempted to clock them with my Bushnell Speedster II Radar Gun. Surprisingly, the radar gun was able to pick up the Lemonheads traveling at 21 mph before they hit me square in the chest. Conclusion number 1: A radargun can pick up objects as small as common caliber bullets.

The next thing I had to test was the speeds involved in shooting sports. Radar guns are rated in mph or kph. Ammunition and arrows are rated in feet per second (fps). Some simple calculations bring out a simple conversion to go from one to the other.

fps x .6816 = mph

Most radar guns, including my Bushnell Speedster II, top out at 200 mph. Using the above formula, this translates to 293.43 fps. The most common load of 45 ACP ammunition is 850 fps. Without question, this is much faster than the radar gun will measure. However, the average velocity of bows for hunting is around 300 fps. The Bushnell Speedster Radargun will probably measure the speed about half the bows out there. The Decatur Prospeed CR-1k Radar Gun will measure speeds up to 310 mph. This figures out to be 454.8 fps. This unit will read the speeds of almost any hunting bow. However, when you compare its price of almost $800 to a common chronograph at $100, it just doesn’t make any sense.

In conclusion, you can use a radar gun as an archery chronograph, but it probably isn’t worth the cost. Have fun playing with them, though.

Ryan

“Remember class, there’s no such thing as a stupid question.”

I had a great question today. “I heard that a car with a supercharger will screw up a radargun. Is this true?”

This is untrue in every way, shape, and form. I can only speculate that they were asking is a supercharger emitted some form of interference that would affect the reading on a radar gun. Superchargers and turbochargers are mechanical units that do not emit any microwaves, electric signals, or radiation. Therefore, they would not affect an electronic device such as a radar gun. If they did emit such interference, would they really be installed in a modern car that is almost completely controlled by electronics?

“Sure, a supercharger will only interfere with a radar gun signal at full throttle, redlined in top gear. Throw the radargun into the grill of the car. Now your mechanical supercharger has interfered with an electronic radar gun.”

Ryan

Ever wonder how a police officer can ticket you for speeding if they are driving? Depending on the model Radar Gun they use, some models have a Moving Mode Radar. These units actually take two speed measurements to figure out your speed. The first measurement is to measure the ground echo, which is the measurement of the patrol vehicle. The second measurement is the target echo, or the speed of the target vehicle relative to the radargun. The difference between these two measurements is the actual target vehicle speed. Moving mode radar guns usually have an accuracy of +/- 2 mph. There are products on the market to help make moving mode police radarguns more accurate. Decatur makes a product called the Vehicle Information Portal for the Decatur SpeedTrak radar system. This unit plugs into the diagnostic port of the vehicle to read the actual patrol car speed through the vehicle’s computer. This unit works on cars manufactured after 1996 that use the OBD II diagnostics computer. Remember, just because the police car is driving in the opposite lane, doesn’t mean he can’t catch you speeding.

Ryan

Radar Guns are all calibrated before they leave the factory. Some are done once, and others are calibrated again before shipping. So how do you know if your radargun is still working properly after years of use? Higher end radar guns such as the JUGSpeed Radar Gun are usually supplied with a tuning fork to check the accuracy. To check the calibration, you must first turn on the radar gun. Squeeze the trigger and release it. Gently tap the tuning fork on a non-metallic object such as a wooden table. You will hear an audible ring coming from the tuning fork. Hold the tuning fork about three inches away from the radargun antenna, with the narrow end pointed at the receiver. Press the trigger again and release. You will see a speed reading on the LCD display. All radar gun tuning forks are stamped with a number. This number should match up with the speed displayed on the radargun LCD display, within a tolerance of +/- 1MPH. (or KPH) If the reading is not within this limit, try again. If you are still getting a large variance between the radar gun and the tuning fork, contact the manufacturer. It’s time to send your radar gun in to be recalibrated.

Ryan

Recently, I have had many requests for permanently mounted radar sensors with remote displays. Most of the time these requests are for building a pitching booth, but there have been a couple fun ones like a new tennis club with indoor courts. For these applications, I have been recommending the Sports Radar DT100 Radar Sensor. This is a permanently mounted unit that is placed behind a catch net and target that the pitcher aims for. The DT-100 senses the ball speed and sends it to a remote display (required and sold separately) such as the Sports Radar DL 731 display. This 7” tall LCD display is easily read from a distance. With the proper software, you can also connect the DT100 to a laptop or PC.

Ryan

Last weekend I went over to my aunt and uncle’s house for dinner. My cousins, ages 4 and 6, just got new bikes so I brought over my Bushnell Velocity Radargun for a little fun. I was amazed at how much fun the kids were when I was clocking their speeds. The radar gun sparked lots of competition and lots of energy in the kids and when all was over we were all ready for bed. My 6 year old cousin just recently threw out the training wheels on his bike, and I think the 4 year old will, too, if I keep bringing my Bushnell Velocity over.

Ryan

We’ve all seen those speed displays on the side of the road. They are commonly found at a toll booth, construction site, school zone, or any place where you are being asked to slow down to a crawl at a quick rate. Some of them are permanently mounted (toll booth) and some are mounted on a small trailer. So what do these speed displays and speed trailers do? The obvious answer is that they show you how fast you’re going. There’s also a lot more that can be going on that you might not be aware of.

Speed Trailers such as the Decatur Onsite 350 have a built in K-Band radargun that tracks speeds in continuous mode. Some models have cameras attached to them that will take a picture any time someone is driving faster than a pre-determined speed. Some even have a strobe light that makes you think you had your picture taken. There are also accessories such as the Decatur EZ Stat PAK Traffic Analysis Software that will track all speeds and produce a Traffic Speed Survey Report that will give information about the flow of traffic in an area to help determine if certain safety measures need to be taken. Even though these units are great for analyzing traffic information, Speed Detection Displays have a primary purpose to get drivers to slow down for safety.

Ryan

If you really want to know how radar guns work, you really need to check out the Traffic Radar Handbook: A Comprehensive Guide to Speed Measuring Systems by Donald Sawicki. This all-inclusive book reminds me of my college Physics textbooks, only with more real world application. The Traffic Radar Handbook explains how the radar gun uses the Doppler Principle to determine speed, the differences between several types of speed measuring systems including RADAR and LIDAR, and the Cosine Effect and how it affects the speeds calculated by the radar gun. Anyone in Law Enforcement should really pick up this book along with anyone who just wants to know how these systems work.

Ryan

Usually, you see police officers in mass force over the holiday weekends. I took the last week off for the Fourth of July, and I did not see a single Police Radar Gun the entire time I was driving through Illinois, Indiana, and Michigan. I can say, however, that I have seen a much greater number of Speed Trailers on the road. Speed Trailers such as the Decatur Onsite 350 SST trailer are good for gathering data on average traffic speeds. Some models include cameras that will take a picture of speed limit violators, while others like the Decatur have a strobe that makes you think you have been photographed. Speed Trailers are a pretty useful tool for construction zones and toll booths.

Ryan

What would win in traffic court, the readings from a Police Radar Gun, or the reading s from a portable GPS unit? When I was asked this question last week, I gave the only answer I could think of. The Radar Gun reading would win. Police Radarguns are calibrated at the factory, certified, and are supplied with tuning forks to test the accuracy. Today, I must give a different answer.

I read in the paper today that there are several cases in Canada and Australia where people are bringing in downloaded GPS data to prove they were not speeding. In more than one case, the GPS readings have provided enough reasonable doubt to let the ticket be dropped. Now, this probably will not work in every situation so I will not guarantee anything, but I think it's time to invest in a nice Garmin Quest 2.

Ryan