Michael Rigby-Jones wrote: >>-----Original Message----- >>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] >>Sent: 21 January 2005 17:19 >>To: piclist@mit.edu >>Subject: [OT] Police "LADAR"? >> >> >>Does anyone know the details on police "LADAR" (laser based >>speed detection). I'm wondering about optical wavelength, >>pulse width, and pulse repetition rate. >> >>Thanks! >> >>Harold >> >> > >This was posted some time ago on http://www.pistonsheads.co.uk, a UK car >forum. The device in question is a Marksman LTI 2020, one of the most >common speed guns in the UK. > >"There is a 905nm Infra red solid state laser module with deam >divergence of approx 3mrad. It flashes 44 pulses of IR over a period of >0.3 seconds. This light is aimed at something very reflective, ideally >the numberplate of a car which who's backing material has the same >reflective properties of a 'corner cube' mirror, known as a reflex >reflector (it reflects light in the direction in which it came to a >tolerence of +/- 3 degrees) The reflected light pulses are picked up by >an IR dependent resistor network behind refracting optics in the LTI >2020 and the time intervals are recorded into memory. The time intervals >plotted against time create a gradient which directly correlates to the >distance travelled by the point of reflection, and therefore the >velocity. The LTI must recieve at least 30 similar reflected pulses to >achieve a legitimate reading. It does this by applying the mathematical >'least squares' algorithm." > >One of the members owns one of these guns, and it seems that it is not >very diffcult at all to confuse it or vastly reduce it's range. Metalic >silver cars have the greatest detection range apparently. > > > Standard microwave guns have problems too. Switching LED arrays held close to the antenna cause a false high-speed reading on one of the most popular units here in the colonies. Its that tiny RF burst that is released when LED's are switched on/off that cause the problem. F-15 cockpit displays had to have a shield within the display glass to stop this, too. >Regards > >Mike > >======================================================================= >This e-mail is intended for the person it is addressed to only. The >information contained in it may be confidential and/or protected by >law. If you are not the intended recipient of this message, you must >not make any use of this information, or copy or show it to any >person. Please contact us immediately to tell us that you have >received this e-mail, and return the original to us. Any use, >forwarding, printing or copying of this message is strictly prohibited. >No part of this message can be considered a request for goods or >services. >======================================================================= > > > -- Note: To protect our network, attachments must be sent to attach@engineer.cotse.net . 1-866-263-5745 USA/Canada http://beam.to/azengineer -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist