How Traffic Radar Works

Traffic radar uses a radar beam to measure speed. Think of the beam as a searchlight. It’s invisible because it’s made of microwaves instead of light, but otherwise it acts very much like a light beam. It travels in straight lines. It’s easily reflected. It scatters as it is passed through dust and moisture in the air. And — this is essential — it has to hit your car before it can determine your speed.

Radar can’t see around corners or through hills. It can’t see you when you are behind another vehicle. When in the clear, how strongly your vehicle reflects determines how far the radar can read your speed. Generally, larger vehicles reflect more strongly than smaller vehicles. Trucks are “visible” on radar farther away than cars.

The principle on which radar operates is absolutely reliable. Radar equipment, on the other hand, is only as good as the quality of its design and manufacture. Traffic radars tend to be unreliable. They’re cheaply made and therefore vulnerable to many interferences that cause false readings. And, compared to the military and weather radar which have rotating antennas, traffic radars are vastly simplified. This simplification means that traffic radar cannot tell one car from another. The operator has to do that, and since the operator can’t see an invisible beam any better than you can, he frequently doesn’t know which vehicle’s speed is being read. This is a source of many undeserved tickets.

How Radar Detectors Work

A radar detector works like a radio tuned to microwave frequencies. Valentine One is an extremely sensitive radio, and it’s tuned exactly to the frequency bands used by all traffic radar in the U.S. — X band, K band, Ka Band, which includes photo. Moreover, it has two antennas, one aimed forward and one rearward, so that it can locate the radar. Because Valentine One is so sensitive, it can easily find radar from the scattering of the beam, and it can find these scatters a long time before the actual beam hits your car. The only exception is Instant-on radar.

How Instant-On Pulse Radar Works

As a defense against detectors, many radar units can be operated in the Instant-on mode, also called the Pulse mode. This means the radar is in position, but it is not transmitting a beam. So it cannot be detected. When the target is within range, the radar operator switches on the beam and the radar calculates the speed, usually in less than a second. This calculation happens too quickly for the target (you) to respond in time. Still, you can defend against Instant-on by recognizing it when the operator zaps traffic ahead of you. Valentine One’s great sensitivity — and your attention to the nuances of its warnings — gives you at least a sporting chance.

The Difference Between X Band and the K Bands

X-band alerts (“Beep”) are often found at long distances. K and Ka bands are usually detected at closer range, and alerts on those frequencies are much more likely to be radar. So Valentine One makes a different sound (“Brap”) to warn you of these more urgent threats (bogeys).

What Are False Alarms

Since all radar detectors are simply radios tuned to the microwave frequencies used by traffic radar, they automatically sound their alert whenever they encounter signals on those frequencies. The problem is, other devices that are not radar are also operating on radar frequencies. A detecting radio must respond to them too. Every response indicates a threat, a bogey. How can you tell the difference between radar and what people commonly refer to as false alarms? Your judgment is the only way. But here are the basics:

  • X band: A catch-all band, still used regularly in some areas by traffic radar, but heavily populated by sensors for supermarket automatic doors and other nuisance signals. In shopping areas, expect door sensors. But know the territory. Unless you’re sure that X band is not used locally for radar, stay alert until you’ve identified the bogey.
  • K band: Maybe radar, maybe not. Supermarket door sensors operating on K have recently begun corrupting this formerly reliable warning of radar. Another non-radar source — cheapie radar detectors that pollute by transmitting on K.
    Identifying Alarms From Junk Detectors Here are a few clues for spotting offending detectors. You may get a brief K warning just as you meet an oncoming car. Or a lingering K, nearly constant strength, as you move with traffic. Big hint: a direction change on the Radar Locator as you pass another car. Look for a detector in the windshield. But stay alert until you know for sure. See page 16 for what “Dee-Dah-Do” tone means.
  • Ka band: Watch out! Most of the new-tech radars operate on Ka. Expect some contamination from cheapie detectors, just as with K (clues above also apply to Ka). Do not dismiss Ka alerts until you’ve positively identified the source.

How To Identify Bogeys

Look first at the Radar Locator. If it points to the side, the bogey is nonthreatening — radar can’t get you from the side. If the Locator points ahead or behind, try for visual identification. And when the Locator changes from Ahead to Beside and then Behind, you can be sure the bogey is safely behind you.

Check the Bogey Counter. Because many non-radar devices occur in multiples. For example, most microwave door sensors have at least two transmitters (for In and Out). Often such an installation will have multiple doors too, so there will be many transmitters. When you see two or more on the Bogey Counter, and particularly when you see it counting up quickly to four or more, you’ve likely found a nest of door sensors.

Burglar-alarm microwave sensors are often multiples too, because a single transmitter is not enough to safeguard an entire building. But microwaves from alarms are less likely to leak out of buildings. So alarms may appear singly or in low multiples.

Single bogeys must be regarded as threats until you see them or put them safely behind you.

Remember, too, that radar beams are easily reflected. Buildings, overhead signs and passing traffic are all good reflectors. When you have a strong signal from one direction, don’t be surprised if the Radar Locator shows brief flickers from another direction also as you drive by reflectors.

And never forget that a brief alert, acting alone, may be 6 Instant-on radar zapping other traffic.

Things to Remember About Radar Detectors
On-The-Road Radar Detector Situations
Radar Detector False Alarms
Radar Detector Testing