The Great Detector Test

The Great Detector Test The Great Detector Test
Comparison Tests

It's been almost five years since our last radar/lidar detector test ( C/D, April 1997). Since all the major manufacturers have either updated their wares or introduced all-new models, the time is right for a fresh look at the high-end segment of the detector market.

Radar is still the most popular form of speed detection-some 100,000 guns are in use, and roughly 20,000 new ones are sold each year. A radar gun works by transmitting a microwave beam at your car. When that beam reflects off the moving vehicle, it changes frequency, and the reflected frequency is used to calculate speed. Traffic radar, which is regulated by the Federal Communications Commission (FCC), operates on three frequency ranges. The oldest is X-band, from 10.500 to 10.550 gigahertz (GHz); about 10 percent of all radar guns use this band. The biggest chunk, about 60 percent of guns, operates on K-band, at 24.050 to 24.250 GHz. Increasingly popular is Ka-band, which spans a wide range of frequencies from 33.400 to 36.000 GHz; Ka-band accounts for 30 percent, including photo-radar units.

Photo radar involves a camera set up at the side of the road that automatically photographs the license plates of speeding vehicles. These devices are popular in Europe, although their use in the U.S. has stalled-just nine police jurisdictions in four states have deigned to rely on them.

Conventional radar can be used in either a stationary or moving patrol car and can transmit its signal coming or going, front or rear. And don't count anymore on using that slow-moving semi-truck in the right lane to shield your smaller but faster-moving Corvette. This technique used to work with older radar guns that would only display the speed of the truck, the stronger reflected signal. Most newer radar guns can clock both vehicles at once and pick out the faster-moving one. The state-of-the-art Stalker Dual DSR radar unit is especially lethal; it can clock cars in opposing lanes or in the same lane the patrol car is in, whether the target is oncoming or moving away. With other units, the officer has to determine whether the gap to the target is opening or closing. The Dual DSR does all this automatically and makes clocking speeders easier than shooting rats in a barrel.

All radar guns can also be set in a steady-state mode and used to monitor traffic continuously. Or the gun can be switched to an instant-on mode in which the operator flicks the unit on and off to instantaneously measure the speed of passing cars. This "instant on" mode is much more difficult to distinguish because the detector must sniff out the occasional brief zap intended for another vehicle in front or behind. Detecting and correctly identifying these brief signals is your only defense.

Because the FCC allows many other devices to operate on the police radar bands, detector warnings do not always signify the presence of police radar. Automatic door openers at markets and malls, burglar-alarm motion sensors, and other devices broadcast on X-band and to a lesser extent on K-band. Some radar detectors even emit a weak signal on a frequency in the Ka-band spectrum, thereby sending false alarms to fellow motorists.

Lidar is another, especially fearsome speed-enforcement tool. A lidar gun works by firing a series of laser light pulses (with a wavelength of 904 nanometers) at a targeted vehicle. The device times the return of the reflected pulses and uses that number to compute the vehicle's speed. The lidar gun sends a narrow beam at its target; even at a distance of 1000 feet, the most intense portion of it is only six feet wide-narrow enough to pick a single car out of a crowd.

But this narrow beam is also the lidar gun's major weakness. Unlike radar, it must be precisely aimed from a stationary position, typically at a range of 500 to 1200 feet. Lidar cannot be used in mobile units. Unfortunately, because there is almost no "signal scatter" for a laser detector to pick up, most detectors can't warn you when Smokey is using lidar until the beam is already focused on your car-and that's usually too late to avoid a speeding ticket.

With roughly 25,000 of these units in use and their numbers growing by 4000 to 5000 a year, lidar represents a very serious threat. Fortunately, detectors are being improved, and on several occasions we've been able to pick up the scatter signal of a laser clocking from a car ahead of ours in time to haul down our speed.

Radar warning has improved, too, but a lot of effort has been focused on "bells and whistles" unrelated to warning drivers of speed-monitoring devices.

Faced with a stagnant market-over the past five years, detector sales have remained stuck at about 1.1 million units per year-manufacturers appear to be searching for the right frills to reawaken buyers.

One detector in this test displays a compass heading; another can record the driver's voice for up to 90 seconds' worth of memos; and features such as weather radio are also being touted.

After 25 years of evaluating detectors, we've refined our technique to a few simple, repeatable tests. To avoid any stray microwave radiation that would produce false alarms, we conducted our tests on the roads of the DaimlerChrysler proving ground in Chelsea, Michigan. Radar testing took place on an unobstructed 2.5-mile straightaway. A gun of each band-X, K, and Ka-was rigidly mounted, one at a time, in a police cruiser that was positioned on a downgrade at one end of the straightaway. By carefully setting each "trap," we adjusted the radar strength so that even the best detector could not find the signal at the far end of the 2.5-mile straight. This type of trap replicates a real-world scenario in which a trooper would be clocking traffic from a low spot in the median or from a dip in the road. It also allowed us to avoid any radar "hot spots" caused by hills and rises that can set off both strong and weak detectors in the same spot.

We tested the detectors' sensitivity, or range, with each radar gun in steady-state and instant-on modes. The farther away a detector sounds its alarm, the more effective it will be at providing a timely warning to the driver. Each detector's sensitivity was evaluated in unfiltered "highway" mode and in the most filtered, or selective, "city" mode. We drove toward the radar guns in both modes and measured the distance at which each detector sounded its first audible warning.

Lidar is used at shorter distances, typically up to 1200 feet. A lidar beam looks like a cone, and a lidar detector must be able to see the weak fringe of the beam, or to pick up weaker reflections off cars in the traffic ahead. We use two different tests to measure a detector's ability to find the edge of that beam or its scattered remnants.

In the first test, we clamped a lidar gun to the top of a stack of cinder blocks five feet high and aimed it precisely at the center of a 32-foot-wide platform 1000 feet away. We then placed each detector behind a piece of windshield glass and moved it laterally toward the center of the platform to determine its sensitivity to the edge of the lidar beam. We do this test with the detectors facing forward and to the rear; this measures each detector's front and rear lidar sensitivity.

Our second test determined the angular field of view of each detector. We mounted a detector in the center of the windshield and then drove forward and backward, at various angles, through a beam aimed across the road. (Police try to keep within an angle of 15 degrees to either side of the target vehicle's line of travel to reduce the amount of error in their speed measurements.) All the detectors in this test respond to a lidar beam within this narrow field, but we think a wide field of view would more reliably enable a detector to see this beam. It should also be better able to pick up any scattered reflections coming off the targeted car.

We conducted two more tests at the proving grounds: one to determine whether the detector is invisible to a VG-2 "detector detector"-a device used by authorities in Canada and states where radar detectors are illegal-and the other to check each detector's propensity to falsely set off other detectors. Finally, we drove a 14-mile urban loop around Ann Arbor to check each unit's resistance to false alarms. Highway mode and most highly filtered city mode were tested.

Unlike other testers, we do not accept samples from the manufacturers, removing the possibility that we might receive a juiced-up ringer unit (this has indeed happened in the past). Each of our detectors was purchased by a nonstaff member and mailed to his home.

As in past detector tests, our numerical ratings are the sum of six separate evaluations as follows: Of a total 100 points, 50 are assigned to a detector's radar sensitivity (range), 10 to its lidar sensitivity, 15 to selectivity (a score calculated by comparing a detector's sensitivity with the number of false alarms it sounds), 15 to its ergonomics (readability of displays, intuitiveness of knobs and switches, mount design, effectiveness of audio warning), 5 points to a calculated city-mode score that compares how well this mode reduces false alarms without diminishing the detector's sensitivity, and a final 5 points are awarded for loudness with the strongest singer receiving 5 points and the weakest just 1.