WHAT YOU SHOULD KNOW ABOUT RADAR
AND RADAR DETECTORS
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
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
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
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 nonradar source — cheapie radar
detectors that pollute by transmitting on K.
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
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
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.