Radar basics: The radar gun emits a radio frequency focused into as narrow a beam as possible then shuts off. The radar beam strikes every hard object in its path and all the reflections are returned to the antenna in the radar gun that is listening for the echoes. The return signal will have been modified by the Doppler Shift effect (frequency expands or contracts proportional to speed difference). The radar gun uses the amount of Doppler Shift (phase angle shift) to calculate the speed of the object that produced the largest return signal.
The opponent, the radar gun: A stationary radar gun can be set for one of several frequency ranges and the distance (power) of the signal. The gun can be set to read speed from a few hundred feet to several miles. A moving radar must also have active speed sensing for the radar unit and compensate the echo reading for the speed of the moving radar gun.
The playing field: In the early 60s the FCC opened up the X band (10.525 GHz; 10.525 billion cycles per second) for general public use. The intended applications could be automatic door openers and burglar alarms which are still used today. Radar guns moved into this frequency ‘band’. X band makes a widely dispersing beam and takes a lot of emitted power to return a signal strong enough to be detected. For a door opener this is no problem but for a long range radar beam this is not so good. Because of these limitations, this band is rarely used for speed radar any more and it is the largest offender for false radar speed control signals.
The FCC opened up additional frequencies for public use over the years to keep up with improving technology. The new bands are K (24.150 GHz) and Ka bands (33.4 - 36.0 GHz). In 1987 photo radar started useing 34.3 GHz. In 1991 Stalker (a brand of radar guns) started using 34.2 - 35.2 GHz and in 1992 BEE 36A (a model of radar gun) started using 33.4-34.4 GHz. Within these frequency bands there are specific ranges which speed control radar is allowed to use, they don’t have use of the whole band. Alerts on K band, and more importantly Ka band, are more than likely to be real traffic radar and not "false" alerts. K and particularly Ka bands produce much narrower beams and do not need nearly so much power to return a useable signal. This reduces radar ‘scatter’ making it harder for radar detectors. The lower power additionally makes it harder for radar detectors.
Radar gun use: Primitive speed control radar in the 60s was shaky at best. The radar units had to be turned on for as much as a half hour to warm up enough to be stable. Some even had mini ovens to hold the components at a constant temperature. The guns operated at high output levels and sprayed a large area with radar waves. This was radar detector nirvana. As technology improved, the guns reached a point where they could simply be turned on and used, but if the beam was shut off it couldn’t instantly turn back on and read accurately. This 'always on' beam was good for radar detectors. Technology moves up. Now the guns can be turned on ‘instantly’ with a pull of the trigger and they can immediately read the return signal – ‘instant on radar’. This gun still needed to have the beam turned on for significantly long times (in electronics terms) to acquire and measure speed. Technology move up. Now guns can turn on and produce a very short signal pulse at very low power (POP) and the gun can still make accurate speed measurements.
Newer guns now use ‘spread signal’ technology were the gun emits more than one frequency when the trigger is pulled. This is an old military radar trick to prevent a signal from being detected.
Radar detectors: The radar detector has one or more internal antennas which feeds a receiver where the signal gets amplified. The signal then goes to a ‘mixer’ where the radar signal gets mixed with an internally generated signal resulting in only one output signal, no matter what the antenna sees. This signal gets sent to a computer controlled signal manager. For a radar detector to ‘see’ X band, the internal signal generator must be altered to an accommodating frequency and sniff for a signal. The radar detector then changes the internal signal to accommodate K band and sniff for a signal, and so on with Ka. If a signal is detected in any of these bands the detector then must determine if it is real speed control signal or spurious (false) like a burglar alarm or door opener. If the software determines the signal is a threat it send an audio/visual alert with a tone appropriate for the band detected. The V1 will also process for signal strengths from all its antennas and illuminate arrows to show the direction of the threat.
The significance of this is that the radar detector is always very busy. It can not ‘stare’ at any one frequency, it has to hop from band to band. With older radar guns this is no problem, they have their signal on long enough for the detector to eventually acquire the signal and do a threat evaluation. The newer POP radar guns produce a signal so short that it simply comes and goes. If the radar detector was looking anyplace but at that very frequency it will miss the pulse, thus no warning. Also, the newer guns use a very, very low power signal which drastically reduces the distance that they can be detected from. Advantage speed patrol.
LASER (LIDAR): [skooter sez]Using the speed of light that the pulse is traveling, it measures the time it takes to hit the target and return to calculate a distance. Then compares that distance with the distances calculated from repeated pulses to calculate the target's speed.[/skooter sez] The light beam is so narrow that the LASER gun usually has to have a scope sight similar to one on a rifle. Because of the pencil beam, there is almost nothing to fan out and scatter so there are no stray signals for your detector to detect. All the officer has to do is pull the trigger on the LASER gun and bam, your day is shot (so to speak).
Working in our favor is the fact that the LASER gun is so precise. LASER enforcement is not mobile, requiring a road side setup. The officer has to stand in the open, track, target and shoot the suspect vehicle. Then must read the speed, run for the cruiser, divest of the gun, buckle up and initiate pursuit. Or, they must work as a team with a spotter and/or gunner, and a chase team. In almost all cases it is hard to hide LASER enforcement if you are observant.
"In almost all cases it is hard to hide LASER enforcement if you are observant."[ponyfool amends] Shooting the target vehicle from behind, from on top of an overpass. If the officer has a steady hand or braces the unit, no windshield mounted laser detector, not even the V1 or X50, will ever even know the speed was measured. The ONLY detector capable of detecting this type of reading is a rear mounted license plate frame sensor, and only then if the officer aims for the plate (which is the typical aiming point because of the reflective material). [/ponyfool]
Detector Detectors; VG-2; Spector: Back to the radar detector and that internal signal generator (super heterodyne). The sensitivity of the detector is related to how strong the signal generator is, so in all quality detectors it is very strong. The bad news is that this signal ‘leaks’, well actually sprays out of the detector and out of your car at very significant power. This frequency is always close to X, K & Ka but not precisely the same as the radar gun frequency. A radar detector detector has an antenna tuned for this slightly off kilter frequency. It works good! Damn good. In fact, the only way you can really hide is to shut off the detector. Radar detector manufacturers have tried to work around this by using a second, different signal generator frequency. This is just too simple and the new detector detectors have no problem anymore. Some new radar detectors claim to be shielded and resistant to detector detectors. While improved, they still are readily detectable, only now, instead of being detectable at miles, the detection range is smaller fractions of a mile. The Radar Detector Detector VG-2 scans the 11.4 to 11.5 GHz range. The Spector, now in I, II, III models scans for radar detectors across a wider range of frequencies.
Police use radar detector detectors (hence forth called RDD) to sense when radar detectors are in use, particularly where radar detectors are illegal. Some police departments consider it useful to know that a car being tracked is using a radar detector. When your detector specifications claim VG-2 and/or Spector it means that your radar detector is shielded with the intention of making it undetectable to VG-2 or Spector RDDs. Some radar detectors like Cobra go so far as to give you an alert that the police are using a RDD in your area.
VASCAR (Visual Average Speed Computer and Recorder): Silent and deadly. This is a manual time/distance calculation. It used to be performed by stop watches and time/distance tables. It is now making a reemergence with modern electronics. The speed control officer will find two reference points and measure the distance between them. As a vehicle passes the first reference point, the timer is started, as the vehicle passes the second reference point the timer is stopped yielding the elapsed time. Straight time/distance calculation yields mph. This is also how aircraft measure speed. If the two reference points are too close together human reaction times will taint the readings, and if the reference points are too far apart depth of perception will effect readings.
RADAR works best when the target vehicle is directly in line with the antenna (180 degrees forward or backward). As the angle between the target and the radar unit becomes less, the speed error goes up (cosine error). With VASCAR the speed observer needs to be as close to 90 degrees as possible.
Pacing: Officer simply moves at the same speed you are, either behind you or shielded by another vehicle. There is no excuse if you are bagged by this technique.
