fjs@nntp-server.caltech.edu (Fernando J. Selman) (02/12/91)
Yes, I did get a ticket. It was a 71 on 55 mph freeway. Because that extra 1 mph is so painfull I would like to know how reliable it is. Somewhere in the ticket it is written "Speeding. K-15". So I assume it was a K-band gunn. Because these devices actually compare the speed of the car with the speed of light, it would imply an accuracy of 1 part in a billion to be able to measure that extra 1 mph. Because of temperature, and humidity effects I would doubt such a reading (it was made in Honolulu). Anyone with advice? References? Should I contend this ticket? Thanks, - Fernando
rsd@sei.cmu.edu (Richard S D'Ippolito) (02/13/91)
In article <1991Feb12.035201.16098@nntp-server.caltech.edu> Fernando J. Selman writes: >Yes, I did get a ticket. It was a 71 on 55 mph freeway. Because that >extra 1 mph is so painfull I would like to know how reliable it is. >Somewhere in the ticket it is written "Speeding. K-15". So I assume >it was a K-band gunn. Because these devices actually compare the speed >of the car with the speed of light, it would imply an accuracy of >1 part in a billion to be able to measure that extra 1 mph. Because >of temperature, and humidity effects I would doubt such a reading (it >was made in Honolulu). Anyone with advice? References? Should I contend >this ticket? Thanks, > - Fernando Maybe, but not on the basis of your technical knowledge of radar operation! I suggest "Introduction to Airborne Radar" by Stimson, published by Hughes Aircraft Company, Radar Systems Group, as a primer on radar. Cheers, Rich
ssave@ole.UUCP (Shailendra Save) (02/13/91)
From article <1991Feb12.035201.16098@nntp-server.caltech.edu>, by fjs@nntp-server.caltech.edu (Fernando J. Selman): > > Yes, I did get a ticket. It was a 71 on 55 mph freeway. Because that > extra 1 mph is so painfull I would like to know how reliable it is. > Somewhere in the ticket it is written "Speeding. K-15". So I assume > it was a K-band gunn. Because these devices actually compare the speed > of the car with the speed of light, it would imply an accuracy of > 1 part in a billion to be able to measure that extra 1 mph. Because First off, they don't use the speed of light to compare with the speed to the car. If anything, they use their own speed for calculations. There are usually two types of radars, one which uses a doppler effect to get your speed, and the other uses phase shift amplitude modulation. Both are pretty accurate. > of temperature, and humidity effects I would doubt such a reading (it > was made in Honolulu). Anyone with advice? References? Should I contend > this ticket? Thanks, The other thing to remember is that usually they do not give away tickets unless you are grossly over the speed limit. Which is upto 5mph above at which point they just give you a warning. The radar beams are quite wide. They return the speed of the largest object they bounch the waves off. So, if there was a truck travelling at 70 in front of you, and you were travelling at 55, but in the fast lane, they are more liable to pull you over instead. If you want to get away with the least trouble and the least fine, always agree with the cop. Tell him that you didn't realise that you were going that fast. Ask him if he was sure. Then tell him that you will be more careful in the future. In that order. If it is your first ticket, you can get it out of your moving violation record by attending a 3 hour class about safe driving. If it is your second or third, forget it. If you have a radar detector in plain view of the cop, expect the worst. Shailendra > - Fernando
little_re@lrc.uucp (02/14/91)
In article <1810@ole.UUCP>, ssave@ole.UUCP (Shailendra Save) writes: > From article <1991Feb12.035201.16098@nntp-server.caltech.edu>, by fjs@nntp-server.caltech.edu (Fernando J. Selman): > If it is your first ticket, you can get it out of your moving > violation record by attending a 3 hour class about safe driving. Your idea about the 3 hour class is great, if the county offers it! I got pulled here (Hickory, NC) in Catawba County for 47 in a 35 and was able to take a "Defensive Driving" class that erased the ticket. However, I got pulled this summer in a county about 3 hours from here (don't remember which), that didn't offer the course. The result was court, for 68 in a 55. Here's an idea : The lawer that I had this summer had me get the speedometer on my car checked. It was off by only 1 MPH, but that was enough for the charge to be changed to Driving With Faulty Equipment. That didn't add any points to my license or raise my insurance. When I got pulled for this, it was on VASCAR not radar. A friend of mine here said that radar has an error of +- 5 MPH. I don't know if that's true (and don't believe it personally), but it might help. Good Luck!! Rich Little Lenoir-Rhyne College Hickory, NC UUCP:lrc!little_re@mcnc.org
johne@hp-vcd.HP.COM (John Eaton) (02/14/91)
<<< < it was a K-band gunn. Because these devices actually compare the speed < of the car with the speed of light, it would imply an accuracy of ---------- Say What? Where did you get this interesting little statement?
fjs@nntp-server.caltech.edu (Fernando J. Selman) (02/14/91)
johne@hp-vcd.HP.COM (John Eaton) writes: ><<< >< it was a K-band gunn. Because these devices actually compare the speed >< of the car with the speed of light, it would imply an accuracy of >---------- >Say What? >Where did you get this interesting little statement? For a doppler radar, the formula to get the speed of the car is: Vcar = 2*(f_dopp/f_rad)*C [that "2" might be 0.5, don't remember] where f_dopp is the doppler shift in frequency, f_rad is the radar frequency (10 GHz for an X band radar), Vcar is the car speed, and C is the SPEED of LIGHT (all electromagnetic waves do travel at this speed in vacuum). The doppler shift in frequency is 29.8 Hz/mph at this frequency, thus, to claim a 1mph uncertainty is equivalent to 29.8Hz/10GHz = 2.98 ppm! This is the power of the doppler effect, that it allow you this type of accuracies, when USED PROPERLY. But I doubt you can eliminate systematic errors to this level using one of the toy guns produced by MPH Industries, Inc. The cop in question had less than a second to make the measurement. I was changing lanes from just passing another car. The uncertainty in the cosine factor would be enough to reduce the speed measured from 71mph to 65mph. The humidity of the day was 82%, even though the manufacturer of the toy gun claim 90% for operational limit, I highly doubt this number as I have never find electronics instruments rated for work above 80% noncondensing. As for the main point in your posting, if the speed of light were to be half that assumed by the logic of the instrument, no amount of calibration would allow you to have a proper reading for all frequencies not equal to the calibrating frequency. The fact that we measure a frequency shift seem to confuse a lot of people into believing that the speed of light is not the gauge in a dopple radar. Refresh your physics! If I posted in this group was to get the knowledge that people that have a lot of experience with chips, solder irons, and bench experience on microwave measurements have about this topic, not just to spread erroneous physics insights in a sarcastic way. - Fernando
squishy@casbah.acns.nwu.edu (Shishin Yamada) (02/14/91)
As the recent holder of a new speeding ticket, also from speed radar. I got clocked at 69 in a 40mph zone on Lake Shore Drive in Chicago at 1 in the morning. There was NOBODY else on the freeway. I wascurious as to the frequencies used for X & K band radar. Are these government frequencies? Does FCC Part 15a apply to a radar signal generator (ie jammer)? I know that often cheap radar detectors will set off one another becuase they usually have a local oscillator that I think connects to an AM Super Heterodyne Receiver. My pink cloud project would be to build a signal generator pegged to a radar detector to turn on when radar signals are detected. However, I do not know the precise effects it would have on Doppler radar (I would expect superposition of the signals), but I do not know what the radar gun's filtering systems are. If this is illegal, how good does a radar gun do. Getting a speeding ticket, just makes me want to buy one even more now. However, I do not know wht good it would do, depending on how fast you can *brake*. -Shishin "Squish" Yamada Northwestern University (EE class of 91) PS: I wound up with the NEW ticket system where I am given 3 choices: A) Pay $50, Plead Guilty. Goes on Record. B) Pay $70, Plead Guilty. Doesn't go on record. Not eligible if you have a ticket within last 12 months. C) Request Court Date. Well, I picked option B. (Sh*t!) As the saying goes: -"Life Sucks! But Death Swallows!"
depolo@eniac.seas.upenn.edu (Jeff DePolo) (02/15/91)
In article <1991Feb14.015812.14576@nntp-server.caltech.edu> fjs@nntp-server.caltech.edu (Fernando J. Selman) writes: >This is the power of the >doppler effect, that it allow you this type of accuracies, when >USED PROPERLY. But I doubt you can eliminate systematic errors to >this level using one of the toy guns produced by MPH Industries, Inc. >The cop in question had less than a second to make the measurement. I was >changing lanes from just passing another car. The uncertainty in the >cosine factor would be enough to reduce the speed measured from 71mph >to 65mph. That's quite a bit of error from the cosine effect. This means that you would have to be off-axis by almost 25 degrees. If the cop was 500 feet away, you would have to be over 200 feet laterally from his position. Considering how wide lanes are, this would be difficult, unless there was a very wide median. Even if being clocked while changing lanes away from the radar gun, your lane-change vector wouldn't come near the 25 degree offset. It's probably on the order of 5 degrees, at highway speeds for a normal lane-change. Say your lane change took 1 second. For a 15 foot-wide lane, this would yield a vector of only 8 degrees off-axis at 70 MPH. Considering a lane change usually takes more than 1 second, this is an overestimate. Both being off-axis and changing lanes away from the radar source would obviously yield a speed reading LESS THAN your true speed, so it doesn't buy you anything in court. >The humidity of the day was 82%, even though the manufacturer of >the toy gun claim 90% for operational limit, I highly doubt this number >as I have never find electronics instruments rated for work >above 80% noncondensing. All of the radar gun info I have gives manufacturer's ratings that are valid up to 90% humidity at 99 degrees. The MPH K-55, however, has a bad reputation of being unstable at high temperatures (per NBS Tests, among others). I've never seen any definate effects of high temperature in the radar guns I've played with, although this is more or less on an experiemental basis and not in an oven in a laboratory. > As for the main point in your posting, if the speed of light >were to be half that assumed by the logic of the instrument, no amount >of calibration would allow you to have a proper reading for all frequencies >not equal to the calibrating frequency. The fact that we measure a >frequency shift seem to confuse a lot of people into believing that >the speed of light is not the gauge in a dopple radar. Refresh your >physics! The doppler shift is directly proportional to the speed of light (radar), true. So, the error in the doppler shift (that is, your speed) is directly proportional to the error in the true speed of light (radar) relative to the design estimate. This error is negligible - we know accurately how fast radar travels to well within a small fraction of a percent. The error induced due to the variation in frequency from the design frequency of the radar gun vs. the true transmitter frequency is also negligible (maybe 10 MHz/10.25 GHz = > .1%). The point is, on a road free of other traffic, free of sources of interference, at a 0-degree angle, with normal ambient temp/humidity conditions, the radar gun should be accurate to well within 1 MPH. If any of the above conditions is changed, all bets are off. Most authorities consider +1 MPH/-2 MPH to be a good margin of error. I consider this wishful thinking. There are too many variables involved in doppler radar to make it foolprof, in particular, target acquisition, interference, proper calibration of the counter, frequency alignment of the transmitter, and proper operation by the operator. In summary, the following things aren't going to help you get off: error in the estimate of the velocity of a radar wave, error in the transmitter frequency of the radar gun, variatons in the speed of the radar wave as it passes through the atmosphere due to changes in density/temperature/ etc. These might work: it was too hot, it was too humid, there was external interference, there was another car around, the gun was not being operated properly, the gun was broken, the gun wasn't calibrated recently, the gun wasn't certified by the State, the gun wasn't checked with tuning forks before and after the stop, martians ate my speedometer (faulty-vehicle approach). The design of the radar gun makes it extremely accurate under perfect conditions - your only hope is to bring up of the less-than-perfect conditions and exploit it. Ignore the theory behind the transition of 10.525 GHz into 71 MPH - the judge just plain doesn't care (he's a lawyer, not an engineer :-) --- Jeff -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Jeff DePolo N3HBZ Twisted Pair: (215) 386-7199 depolo@eniac.seas.upenn.edu RF: 146.685- 442.70+ 144.455s (Philadelphia) University of Pennsylvania Carrier Pigeon: 420 S. 42nd St. Phila PA 19104
depolo@eniac.seas.upenn.edu (Jeff DePolo) (02/15/91)
In article <3498@casbah.acns.nwu.edu> squishy@casbah.acns.nwu.edu (Shishin Yamada) writes: >As the recent holder of a new speeding ticket, also from speed radar. I got >clocked at 69 in a 40mph zone on Lake Shore Drive in Chicago at 1 in the >morning. There was NOBODY else on the freeway. I wascurious as to the >frequencies used for X & K band radar. X: 10.525 GHz K: 24.150 GHz >Are these government frequencies? No. They are classified as "radiolocation". They are also shared allocations. For example, some motion-sensors used for opening the doors at your local supermarket are on 10.525 GHz. 24.150 is in the middle of the amateur radio 24 GHz band. >Does FCC Part 15a apply to a radar signal >generator (ie jammer)? No. Intentional jamming or interfering with another radio (radar gun), whether the device is a part 15 device or not, is illegal. Radar guns are part 15 devices, but that doesn't mean that you can maliciously jam them. It just means that other devices being operated for a valid reason can interfere with the part 15 device legally. >I know that often cheap radar detectors will set of >one another becuase they usually have a local oscillator that I think >connects to an AM Super Heterodyne Receiver. Not quite. The echo signal is mixed with the original signal in a nonlinear device (a detector diode or the Gunn diode itself) and the difference frequency is fed to a counter or PLL (or, in moving radar, into 2 counters or PLL's). >My pink cloud project would be >to build a signal generator pegged to a radar detector to turn on when >radar signals are detected. However, I do not know the precise effects it >would have on Doppler radar (I would expect superposition of the signals), >but I do not know what the radar gun's filtering systems are. This is how most radar jammers are supposed to work. You pulse a X band/K band signal (doesn't have to be right on his frequency) to cause a perceived doppler shift in the radar gun. The speed at which you pulse is the frequency you want to be displayed on smokey's gun. >If this is illegal, how good does a radar gun do. Getting a speeding >ticket, just makes me want to buy one even more now. However, I do not know >wht good it would do, depending on how fast you can *brake*. Braking VERY hard will often cause no readings. Most radar guns have some sort of a verification system. It will re-sample the counter's result a few times (like 5 or 10 or whatever). If all of the numbers come up the same, it displays the reading. If not, it leaves the display blank. Hence, if you're braking hard enough, you can "beat the gun". Don't do it with anyone behind you or they'll get a macroscopic view of your license plate. Most of them are able to do the initial validiation in about 1/2 to 3/4 second, and then 2/10 of a second thereafter on subsequent checks, so your key is to start braking AS SOON AS your detector goes off. Note that you usually have less time when the radar gun is operating from a fixed position (Kustom's stationary-only guns like the Falcon are deadly in this respect - they can lock in about 2/10 second on the first fire). Moving mode guns have to validate two readings (the cop's ground speed as well as yours) so you have a bit more time, but still not much. --- Jeff -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Jeff DePolo N3HBZ Twisted Pair: (215) 386-7199 depolo@eniac.seas.upenn.edu RF: 146.685- 442.70+ 144.455s (Philadelphia) University of Pennsylvania Carrier Pigeon: 420 S. 42nd St. Phila PA 19104
smithj@hpsad.HP.COM (Jim Smith) (02/16/91)
>add any points to my license or raise my insurance. When I got pulled for >this, it was on VASCAR not radar. VASCAR, eh? I haven't heard of this in years. Didn't know it was still being used! Wasn't there a problem with having to make a subjective judgement of when the target car and the police car passed the same point?
jgk@osc.COM (Joe Keane) (02/16/91)
The original poster is correct about comparing your speed to the speed of light. The ratio between the beat frequency and the original frequency gives your speed relative to the speed of light. Actually, the ratio is twice your speed, but this obviously isn't important. However, i don't agree with the statement about requiring parts per billion accuracy. The beat frequency is typically about 10^7 times lower than the radar frequency. But this doesn't matter, if you know both frequencies to parts per thousand, then you know the ratio to parts per thousand too. Note that we don't need to know either frequency, just the ratio. Measuring the ratio between frequencies can be done extremely accurately. For example, you can clock a counter at the radar frequency, or more likely some oscillator which is multiplied to give the radar frequency. By counting the number of cycles between zero-crossings of beat frequency, we get the inverted ratio to the closest whole number. With this scheme it doesn't matter if the radar frequency is off. The ratio, and thus your speed, are still right. So i don't think there are any theoretical limitations on accuracy. What's more important are the practical problems: interference by random signals, components going out of spec due to heat or humidity. These are the things you should concentrate on if you want to beat the ticket.
kthompso@entec.Wichita.NCR.COM (Ken Thompson) (02/18/91)
Paying more to not have the ticket on one's record does not sound LEGAL to me. -- Ken Thompson N0ITL NCR Corp. 3718 N. Rock Road Wichita,Ks. 67226 (316)636-8783 Ken.Thompson@wichita.ncr.com
depolo@eniac.seas.upenn.edu (Jeff DePolo) (02/19/91)
In article <1991Feb17.064619.27255@athena.cs.uga.edu> mcovingt@athena.cs.uga.edu (Michael A. Covington) writes: >Here are some things I learned recently while serving on a jury: > >(1) Accuracy to +- 1 mph is definitely _not_ to be expected. +-5 mph is >believable. The biggest source of errors is from measuring the wrong >vehicle. Accuracy to +/1 MPH is REQUIRED (see #2 below). The +/- 5 MPH due to multiple vehicles makes no sense. The radar gun is going to return the speed of one of the vehicles behing clocked. The problem is that you don't know which vehicle it is. Hence, the accuracy is still within tolerance, only you don't know which vehicle is the target. Consider one car passing another (55 MPH and 75 MPH). While the passer is behind the passee, chances are that the radar gun is going to return the lead car's speed -- 55 MPH. When the passer passes the passee, the radar will probably read 75 MPH. Hence a 20 MPH difference. This is NOT a +/- 20 MPH error in accuracy. It's right on the money. With a lone target on a road, accuracy will be within +/1 MPH, minus cosine error, assuming no external interference. This is theoretically, practically, and experimentally true. >(2) Radar guns are calibrated with tuning forks (strange but true). Not exactly. They are checked with tuning forks. Stationary-only radar guns usually have one or two forks. Each should return a particular reading (like 45 and 75 MPH). If the speed displayed is off by more than 1 MPH, the radar gun is supposed to be taken out of use. For moving-mode radar guns, there are two forks (like 120 MPH and 55 MPH). Striking the two and holding them both in front of the radar gun should yield a "patrol" reading of 55 and a "target" reading of 65. When radar guns are calibrated, they are done so with real test equipment, such as frequency counters, signal generators, etc. The tuning forks are only used for in-the-field accuracy checks, not for calibration. There's a big difference here. >(3) A radar gun requires an FCC license to operate. In Georgia, the >police must produce this license, in court, in order for radar evidence >to be admissible. True. >(4) Any other transmitter on radar frequencies would require a license, >unless there's a loophole in Part 15 after the revision. (Part 15 governs >license-free transmitters and has just been liberalized.) In any case, >the transmitter would be illegal if its purpose were to interfere with >a licensed user of the radio spectrum (the radar). There are many many many part 15 devices that operate inside the radar bands. Neither X nor K band is a police-only or radar-gun-only allocation. The X band is shared with part 15 devices, such as microwave door openers, alarm systems, etc. among others. The K band is shared with Amateur Radio among others. Part 15 devices like door openers don't require a license. In any event, jammers would not be considered Part 15 devices, as their intent is to interfere with another service. --- Jeff -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Jeff DePolo N3HBZ Twisted Pair: (215) 386-7199 depolo@eniac.seas.upenn.edu RF: 146.685- 442.70+ 144.455s (Philadelphia) University of Pennsylvania Carrier Pigeon: 420 S. 42nd St. Phila PA 19104
rsd@sei.cmu.edu (Richard S D'Ippolito) (02/20/91)
In article <4518@osc.COM>, Joe Keane writes: >The original poster is correct about comparing your speed to the speed of >light. This is still misleading -- your speed is not compared to anything, much less the speed of light. Your speed (actually, the radial component of relative velocity) is what is being determined! Rich
henry@zoo.toronto.edu (Henry Spencer) (02/20/91)
In article <3498@casbah.acns.nwu.edu> squishy@casbah.acns.nwu.edu (Shishin Yamada) writes: >Are these government frequencies? Does FCC Part 15a apply to a radar signal >generator (ie jammer)? ... There are a variety of users in that general band, but I think police radar is the only authorized user of the specific set of frequencies used. Mind you, the receiver on the radar's input probably isn't that selective, and could probably be jammed by a frequency outside the police allocation. However, interfering with a police officer in the performance of his duties is a *serious* crime, the sort that results in jail and a criminal record rather than just a traffic ticket and more expensive insurance. Don't expect the police to have a sense of humor about deliberate jamming; they will throw the book at you. At the very least, you'd better have a lawyer picked out before trying it. -- "Read the OSI protocol specifications? | Henry Spencer @ U of Toronto Zoology I can't even *lift* them!" | henry@zoo.toronto.edu utzoo!henry
pfluegerm@gtephx.UUCP (Mike Pflueger) (02/22/91)
In article <37842@netnews.upenn.edu>, depolo@eniac.seas.upenn.edu (Jeff DePolo) writes: > the speed of one of the vehicles behing clocked. The problem is that > you don't know which vehicle it is. Hence, the accuracy is still within > tolerance, only you don't know which vehicle is the target. Consider > one car passing another (55 MPH and 75 MPH). While the passer is > behind the passee, chances are that the radar gun is going to return > the lead car's speed -- 55 MPH. When the passer passes the passee, > the radar will probably read 75 MPH. Hence a 20 MPH difference. This I'd like to add a comment here - and one which CAN be used as a defense for radar speeding tickets. Possibly the best "technical" defense. Due to the relative received signal strengths, the capture effect, and radar guns' electronic bias, the stronger return will override the weaker one. Received signal strength being roughly equal, the FASTER speed will be displayed. So, if you're in front of (or behind) a semi rig in your compact car, within say 150 feet, in a freeway situation, an oncoming cop may never pick up your speed - the radar'll probably only see the truck. I believe radar guns have about a 3 degree beamwidth. At 1000' (1/5 mile, roughly the detection range), the radar beamwidth is 105'. Consider the angles and the radar is illuminating a LONG stretch of the oncoming lane. Not only is the size of the vehicle a big factor in reflected signal, but shape and even the construction play a part. I can vouch for the 1977 corvette being noticably stealthy - it doesn't seem to return a reliable reflection until about 500' for hand held K band units :-) There are a lot of factors involved in reflected signal strength. Suffice it to say that if there are any cars near you and the cop is coming toward you (or shooting your lane at a shallow angle), it can be very tough to determine (for sure) which vehicle is being clocked. Now, if he's shooting more across the lane or no one else is around, that's a different story... -- Mike Pflueger @ AG Communication Systems (formerly GTE Comm. Sys.), Phoenix, AZ UUCP: {...!ames!ncar!noao!asuvax | uunet!hrc | att}!gtephx!pfluegerm Work: 602-582-7049 FAX: 602-582-7624 Home: 602-439-1978 Packet: WD8KPZ @ W1FJI Internet: PLEASE USE UUCP PATH (NOT INTERNET)!
dag@hp-lsd.COS.HP.COM (David Geiser) (02/26/91)
In sci.electronics, pfluegerm@gtephx.UUCP writes: p> p>I believe radar guns have about a 3 degree beamwidth. At 1000' (1/5 p>mile, roughly the detection range), the radar beamwidth is 105'. p>Consider the angles and the radar is illuminating a LONG stretch of p>the oncoming lane. The specs on the two that I have are much wider than 3 deg., regardez: MPH Industries K-55 radar unit UNIT OPERATING SPEED: Patrol- 20MPH to 55MPH (above 55/below 20 available on request) TARGET SPEED: 20MPH minimum to maximum 209MPH closing speed 20MPH to 100MPH while patrol is stationary SPEED VALIDATION: target speed 50MPH: 100 comparisons in 1/8 sec. target speed 70MPH: 140 comparisons in 1/8 sec. RFI PROTECTION: when excessive RFI is present, no readings will be displayed CALIBRATION ADJ: NONE- fixed TIME BASE: Crystal oscillator +- 5 % LOCK TIME: Instantaneous ACCURACY: +- 1MPH Absolute ANTENNA ANTENNA TYPE: Circularly polarized conical horn OPERATING FREQ: X-Band: 10.525 GHz +-21.05MHz K-Band: 24.150 GHz +-48.3MHz OUTPUT POWER X-Band: Nominal 13-30mW Maximum 50mW K-Band: Nominal 12-50mW Maximum 95mW RADIATED PWR DEN: < 1mW/cm^2 @ 5cm (in accordance with microwave oven stds.) BEAM WIDTH: X-Band: maximum 18 degrees K-Band: maximum 15 degrees SIDE LOBES: 24dB down from main beam RANGE: 2500 feet for avg vehicle size. Range varies by size of vehicle, terrain, weather. AND THE EVER POPULAR Ka-BAND RADAR UNIT (made by Zellwager Uster AG [Switzerland] for Traffic Monitering Technologies of Friendswood Texas) UNIT MEASURING DIRECTION: Oncoming traffic MEASURING RANGE: 15MPH to 155MPH MEASURING ACCURACY: <= 100MPH +- 1MPH > 100MPH +- 1% ELECTRONIC FLASH: 170W/340W RECHARGE TIME: 170W 0.9 sec. 340W 1.8 sec. ANTENNA TRANSMIT FREQUENCY: 34.3 GHz +- 100MHz TRANSMITTED POWER: 0.5mW MAXIMUM TYPE OF ANTENNA: parabolic reflector HALF-PWR BEAM WIDTH: 5 degrees horizontal 5 degrees verticle SECONDARY LOBE ATTEN: > 20dB MEASURING ANGLE TO DIRECTION OF TRAVEL: 22 degrees RANGE: Designed for 50 feet with downward transmission @ 22 +- 3 degrees beam width. Beam makes 5 degree angle with ground at 50 feet.
depolo@eniac.seas.upenn.edu (Jeff DePolo) (02/26/91)
In article <231@alpine.gtephx.UUCP> pfluegerm@gtephx.UUCP (Mike Pflueger) writes: >I'd like to add a comment here - and one which CAN be used as a defense >for radar speeding tickets. Possibly the best "technical" defense. > >Due to the relative received signal strengths, the capture effect, and >radar guns' electronic bias, the stronger return will override the weaker >one. Received signal strength being roughly equal, the FASTER speed will >be displayed. I don't see the reasoning behind this. If the two returns are the same is strength, there is no reason why the gun would display the faster of the two. All of the radar guns I've played with (4 different models) will typically alternate between two readings if there are two targets relatively "equal" in strength. However, as you made mention of, some radar guns are biased to choose the faster speed when give the choice. This is a bad idea. Whenever there is a bias in the counting circuitry such as this, it leads to many problems with target identification. With respect to capturing - there is no capture effect, such as in FM communications. In it's pure form, a radar gun is just a transmitter, receiver, mixer, and audio-frequency counter and scaler. The only place capturing can occur is in the counter. A frequency counter has no capture-ability - it just counts. Some radar guns use PLL's instead of pure counters, in which case, the PLL may "capture" the signal, but if designed properly, the radar gun should be able to quickly "unlock" the current signal and lock on the stronger one. >I believe radar guns have about a 3 degree beamwidth. At 1000' (1/5 >mile, roughly the detection range), the radar beamwidth is 105'. >Consider the angles and the radar is illuminating a LONG stretch of >the oncoming lane. The tightest patterns are on the order of 12 degrees these days. One of the most popular units, the MPH K55, had a beamwidth of over 24 degrees on it's initial models (Model I, aka 1979 version). The X band K55's they are selling now are in the 18 degree range. You'll typically find wider beamwidths on the X band guns due to size limitations of the antenna horn. >Not only is the size of the vehicle a big factor in reflected signal, >but shape and even the construction play a part. I can vouch for the >There are a lot of factors involved in reflected signal strength. Suffice >it to say that if there are any cars near you and the cop is coming toward >you (or shooting your lane at a shallow angle), it can be very tough to >determine (for sure) which vehicle is being clocked. Now, if he's shooting >more across the lane or no one else is around, that's a different story... If he's shooting across the lanes of traffic at more than a few degrees off-axis, you have the cosine effect in your favor, however. If you're all alone, well, sorry. --- Jeff -- -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Jeff DePolo N3HBZ Twisted Pair: (215) 386-7199 depolo@eniac.seas.upenn.edu RF: 146.685- 442.70+ 144.455s (Philadelphia) University of Pennsylvania Carrier Pigeon: 420 S. 42nd St. Phila PA 19104
vail@tegra.COM (Johnathan Vail) (02/27/91)
In article <791@entec.Wichita.NCR.COM> kthompso@entec.Wichita.NCR.COM (Ken Thompson) writes: Paying more to not have the ticket on one's record does not sound LEGAL to me. Legal means according to the laws. They make the laws so it must be legal. Remember that the whole issue of speeding, except for extreme cases, is just another form of taxation. Think of the higher fee as just another tax bracket. "Did you ever walk into a room and forget why you walked in? I think that's how dogs spend their lives." -- Sue Murphy _____ | | Johnathan Vail | n1dxg@tegra.com |Tegra| (508) 663-7435 | N1DXG@448.625-(WorldNet) ----- jv@n1dxg.ampr.org {...sun!sunne ..uunet}!tegra!vail