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Part Two of Two

DEDICATION - This article is dedicated to all of you who worked midnights December 25th. You are not forgotten. All of us here at SWS and Police &  Security News offer our sincere best wishes for a happy, healthy and  prosperous new year. Mankind may be callous, but God will not overlook those  who unselfishly serve their fellow man. Committed public servants are some of  the most special people we have. Thank you.

 What a month! It was good to renew old friendships and make many new ones at  the Council of International Investigators annual meeting and the Federal Investigators' symposium this last month. Thanks, everybody, for the kind  words about these articles, the many calls, letters and encouragement.  Apparently many of you are very interested in bumper beepers. Well, here's part two. As always, we encourage feedback, assault and flattery, and ideas  for future articles.

 Last month we introduced the bumper beeper. As a very brief recap (read last  month's article if you haven't already...), bumper beepers are special purpose  direction finders designed to let you follow a target vehicle efficiently. They consist of a small beacon transmitter usually  affixed magnetically to the car under surveillance, and a companion  receiver operated in your vehicle. A series of indicators on the  receiver give you a bearing from your car to the target, and signal  strength (which can be extrapolated to relative range). To snag the signal from the transmitter, you erect either two or four magnetic antennas on the roof of your vehicle, depending on whether your unit  indicates 180 degree bearings (two antennas) or 360 degrees around your vehicle (four antennas).

 Since it's so important, again I'll mention that experience and understanding the basics of direction finding are vital to a successful  moving surveillance. Do not expect these things to point you to the target vehicle without several hours of practice under various  conditions, heavy traffic in congested areas and in busy downtown areas as well as suburban or rural terrain. You might consider working with  another investigator who's had a bit of experience and can help you get  started.

 Several accessories will make life a bit easier if you're going to use  a tracker on a regular basis. Consider adding the following to your bag of tricks. I'll explain the reasoning behind each item in the remainder  of this article.

 Narrow bladed, sturdy putty knife or similar scraper
Strong plastic bag large enough to enclose transmitter
Foil packages of hand cleaner towelettes
Roll of dark colored, non glossy duct tape
Roll of good quality electrical tape
TWO sets of batteries, new and date coded, for both the  transmitter and receiver
Small penlight that works

 To try to keep things interesting, but at the expense of logical flow,  I'll intersperse theory with practical tips. Try to follow the theory though - it will help in the long run and we'll keep it to a minimum.  OK?

 There is a world of difference between direction finders specifically designed for tracking moving vehicles and those originally intended for  finding illegal CB radios, sinking ships, clandestine spy transmitters, or meese (plural of mooses) wandering the open plain. And,  unfortunately, most of the "vehicle" tracking systems widely marketed  to the investigative community are converted units such as the above. Merely packaging a battery operated transmitter in a box with magnets does not a bumper beeper system make. I would suggest you speak with the manufacturer or his representative and ascertain the design purpose  of his unit. Ask for a copy of the instruction manual. Does the sales literature specifically discuss investigative applications? Is the manufacturer in tune with the needs of the professional investigator?  The answers to these questions should help you select a vendor, which  is the first step to selecting an appropriate tracking system.

 There are several technologies applied to direction finding. Based on our rather extensive research and hundreds of hours in the field using the various packages, only one is well suited for tracking a moving  vehicle. Remember, as we covered last month, we are trying to lock onto  a pipsqueak signal from a small antenna surrounded by metal only a few inches from the ground. These are heavy duty requirements that must be  handled properly or you will not be happy. The proper system, used by a man who knows what he is about, will work fine. Take away one of these factors and you will have an expensive, useless toy.

 There are three types of direction finding receivers found in the field today. They are: Adcock, Doppler and switched pattern. All work, and  all work well for their intended applications. Of all three, however, the switched pattern is the only one really suitable for investigative use. I am not including in the above the simple, although popular,  signal strength type devices which merely tell you through a varying  tone or series of lights whether you are moving closer or further from the transmitter.

 The signal strength devices sometimes also include a  directional antenna (beam, or Yagi) which looks like a small TV antenna built on a broomstick and is intended to be held out the window of your  vehicle and rotated for the strongest signal. The direction the antenna  is pointing when the signal is strongest is the bearing to the transmitter. Read the fine print in the ads. A beam antenna is a giveaway to signal strength devices, which are pretty much worthless for our kind of tracking in the real world. Directional antennas have their use, but only in the hands of a for real radio professional, and then almost never for vehicle tracking. Stay away, also, from any  tracking system which only uses one antenna. As far as I know, it is  impossible to derive bearing information with only one non directional antenna. As I constantly stress, dealing with a knowledgeable supplier  who will work with you is the best way to end up with the best value in equipment. There is one rather well known west coast manufacturer of an Adcock  system. This manufacturer is about as interested in your successful tracking as the IRS is in your pursuit of happiness, but both are about as equally interested in how much money you can cough up. Aside from this, Adcock has an advantage of low profile antennas which can be  disguised rather easily. Note that my use of the term Adcock is a generic term that refers to a technique of deriving bearing information  rather than the name of a manufacturer, which I'm not allowed to mention in an open forum. My phone number is (410) 879-4035. An Adcock  system, approximately, uses four vertical antennas in a box pattern with a fifth antenna, called the sense antenna, in the middle.

 Appropriate electronics compare the transmitter's signal as received by the sense antenna to that received by the other four. The results of this comparison are displayed on some sort of indicator that tells you  where the target transmitter is in relation to your vehicle (actually,  in relation to the antenna array, which is presumed to be mounted on your vehicle). The indicators are pretty much the same for all tracking systems. The system sold by the manufacturer mentioned above is unique in that it displays bearing information on a CRT (like a small TV  screen). Your vehicle is in the center, displayed as a dot. The system draws a line from the center to the edge of the screen face, the vector  of which indicates the relative bearing to the target. There is an  advantage to this graphic display other than bells and whistles in that certain types of multipath interference (see part 1) is shown as garbage on the display. With some practice and trial and error you can tell by looking which displayed vector is most likely to be genuine.

 The Adcock system tends to be considerably larger than what is  considered practical for mobile applications. Again, if you're on a  Coast Guard ship, this is not a problem. If you're in a standard  passenger car, it is. The Adcock technology works well for very short  pulsed signals. Short pulsed signals (though they must be repeated frequently) tend to be associated with data transmissions or pulsed  encoding techniques such as might be used in surreptitious  transmissions to and from a satellite. Bumper beeper pulses are infinitely long compared to the short bursts in which the Adcock excels.

 We need to digress for a moment and discuss an important factor relating to antennas. Please follow along here and call me if this info  is not clear, because it is vital to proper vehicle tracking. There is  a term used in reference to antennas known as "polarization".  Polarization, briefly and approximately, means the orientation of the radio waves leaving (or arriving) at an antenna. Vertically polarized  signals emanate from an antenna that is vertical - like your car radio antenna or a handheld radio antenna. Horizontally polarized signals are  used with broadcast TV - look at the TV antenna on your roof for an example of a horizontally polarized antenna. The important point to remember here is that signals must maintain the same polarization or severe losses will result - and, for vehicle tracking applications,  cross polarized signals will cause unacceptable errors in bearing  information. We might simplify things by saying that antennas that are  perpendicular to the ground are vertically polarized. Antennas that are parallel to the ground are horizontal. And rarely the twain shall meet.

 Why do we need to concern ourselves with polarization? Well, virtually  every application you and I will have for vehicle tracking will be  vertically polarized. The two (or four) receive antennas mounted on the top of your vehicle are vertically polarized. Ideally, the transmitter's (beeper's) antenna should be vertically polarized for best signal strength and most accurate bearing information. But here arises a problem - many, if not most, of the tracking systems we've seen in the field use what we refer to as a "dribble" antenna. This is an extremely flexible stranded wire antenna which is left to flop out  of the bottom of the beacon transmitter.

 The idea of a flexible  antenna, on its face, has merit in that you can't always give the antenna a clear shot to the atmosphere when the transmitter is buried in the underbelly of the car. However, this is the classic situation  where someone knows enough to be dangerous. I realize I frequently  sound cynical, but it's obvious from the design of the product, the  advertising, and conversation with the manufacturers and their reps that none of them truly know anything about vehicle tracking. There is more to successful vehicle tracking than packaging a small transmitter  in a box with batteries on the inside and magnets on the outside. Forget the soapbox. A dribble antenna, by its flexible nature, will  blow around in the wind, from vehicle vibration, etc., AND CONSTANTLY  BE CHANGING ITS POLARIZATION from vertical to horizontal or some useless permutation of the two.

 This, we have found in our field  trials, is a critical problem with vehicle tracking systems. You can  understand, based on what we've just covered on polarization, that if  the polarization is not constant, the signal strength and other  parameters will vary, causing serious errors in what your receiver will faithfully try to tell you. The bottom line? Any tracking system  (transmitter) that uses a flexible wire antenna is probably designed by someone who really doesn't understand vehicle tracking. That being the case, you might consider whether you want to deal with such a critter. Unless you know EXACTLY what you are doing, do not buy a beeper transmitter that uses a dribble antenna. You might have some fun, when you're talking to the vendor, asking him what antenna his unit has, and  why. Maybe he will have read this article, though.

 What is the alternative? Simple. A copper wire antenna that is stiff  enough to stay how you put it. Our unit uses a regular piece of #14  solid copper wire (insulated, of course). You can bend the antenna  however you need to clear the underbelly of the car, even if that  requires odd shapes. And the antenna length at VHF frequencies where  many tracking systems operate is about 16 inches. Obviously we can't  deal with that long an antenna so ours is coil loaded down to about 6  inches. What this means is that the antennas are special and can't be substituted. If you need another antenna, call us and get the proper one - they're cheap and anything else won't work right. Antennas are as  critical as tires on a car - they are what couple the transmitter to the atmosphere. Everything hangs on the antenna so please don't accept any compromises.

 If you have a beeper transmitter that uses a dribble antenna, we might  be able to do something to improve it for you. Call our office to discuss it.

 I can guarantee that within a few days after this article hits the  streets I will get a number of calls from owners and vendors of the  "junk" trackers who will claim that their units work just fine. To this I will politely respond with something to the effect that if all you've ever used is a zip gun, you can't appreciate a target pistol. Also, there is a very human tendency to rationalize either something which you have bought, or something that you sell. Once you have used a quality piece of equipment you will not ever want to fool with anything less. We find the same thing with night vision. To someone who's not familiar with state of the art, a military surplus piece with an  alphabet soup part number will seem impressive. Try a Dark Invader for an evening and you will give the jungle scope to a kid as a toy to take  apart (I did).

 Wow! What a digression from a discussion on polarization. The reason I  led into polarization was to mention that the Adcock technology of  direction finding works very well with vertically polarized signals. It does not work very well with signals of mixed polarization, such as  might be found in vehicle tracking applications. Other methods of processing tracking information handle varying polarization better than  Adcock.

 There are many systems out which operate on a principle called Doppler. The Doppler systems are characterized by four antennas. By their nature  Doppler systems are 360 degree devices - you remember what we said about 180 vs. 360 in part 1. Doppler systems (generically, not the company known by the same name), are relatively less expensive to produce than some of the others we will be discussing, and therefore  find their way into some of the quick buck operations. Doppler  direction finding is certainly a viable technique, and has its place -  but that place is not for vehicle tracking.

 Doppler receivers are characterized by a compass "rose" of lights, perhaps 36 of them  arranged in a circle for all 360 degrees. Theoretically only one light  at a time should be on, although with severe multipath you'll get lights everywhere and all bets are off. We have performed extensive  field testing on Doppler systems and have found that they seem to need  a relatively stronger signal to indicate accurately than their  associates. Doppler systems work by comparing the transmitter's signal  as received by the four antennas and deciding with intelligent electronics which antenna is closest to the transmitter. (This is a  very crude and not too accurate description, but anything more technical would be beyond the scope of these articles).

 Dopplers are quite reliable at determining bearings, but not too  terrific at determining range. This does not mean that the other  systems do determine range, rather that the others are able to make a more accurate extrapolation of range vs. signal strength than the Dopplers. Dopplers are also considerably more tricky to operate in built up areas such as busy concrete jungles. One advantage of Dopplers  (for spies, maybe) is that they can give accurate bearing info with a  very quick transmissions. If you're DF'ing a pirate transmitter that  only says one word every few minutes - maybe in the instance of a stolen radio that found its way back onto your system - the Doppler would be a good route to go. For vehicle tracking applications, though,  the advantage of locking onto quick transmissions is relatively unimportant and not, in my opinion, worth the tradeoffs in other areas.

 Ok. Now that we've discussed what NOT to buy, what should we use? The best type of direction finder for moving vehicle tracking is the technique known as "switched pattern". Some good tracking systems are  available using switched pattern; sources include several three-letter named private manufacturers of police electronics systems. Switched pattern involves two (or four, for 360 degree coverage) antennas which  are alternately "switched" one at a time to the input of the receiver.  Our unit switches 120 times each second, not that we need to know or care. By the system knowing the placement of the antennas on the roof of the vehicle (remember the emphasis on antenna placement in part 1), and the approximate "pattern" of the antenna, the signal received from the beeper transmitter will be stronger on one antenna in the system. As the system knows which antenna hears better, and where it is on the car, the receiving electronics can reliably derive bearing information. Due to the fact that only one antenna is actually connected to the receiver at a time, multipath is easier to discriminate. Switched  pattern systems excel in areas of most concern to vehicular applications.

 They do not care as much about polarization (even though  it doesn't hurt to keep the polarization as close to vertical as possible), are usable in all types of terrain, can accurately translate  signal strength into relative range (with the help of the operator's  wealth of experience), and can track fine on weak signals. In fact,  with our unit we have demonstrated long range tracking on signals that  were too weak to be heard through the speaker. And, another major  consideration, the switched pattern is one of the easiest systems to learn the techniques of vehicle tracking with.

 The ORION unit that we  handle displays bearings on a zero center meter. As we discussed last month, the meter reading center indicates roughly that the target vehicle is directly ahead of you. A needle showing left or right of center means that's where the vehicle is, and indicates the direction  in which you should steer your vehicle to stay on the target. The whole  receiver package is small, about the size of two reams of xerox paper stacked, and is built into a weatherproof Haliburton suitcase. On  internal batteries the unit is good for better than 24 hours of  continuous tracking, or it can be plugged into the vehicle's cigarette  lighter for extended duty. If you're running a moving surveillance for more than 24 hours, anyway, you're a marathon operator qualified for  the surveillance olympics.

 In addition to the meter indicating bearing, there is another large face meter which displays signal strength. With some experience signal  strength information can tell you a lot about what the target is doing. A remote panel is available to mount the meters on the dash of your car  if you're working alone and don't want to keep glancing down at the  seat next to you while you drive.

 I guess all the above can be summarized rather briefly. Buy a unit that was designed specifically for law enforcement vehicle following. Stay  away from units originally designed for Coast Guard, military, tracking meese, or "public safety" use. Unless you have specific technical  requirements, in which case this article won't teach you a thing, select a switched pattern tracking system. Do not accept a transmitter that has a flexible wire antenna, or if you have one already call someone like us to install a solid antenna on your existing transmitter. Don't buy any system that uses a single antenna on the  receiver, or mentions a directional, beam or Yagi antenna. DO know and trust your supplier, and make sure he is familiar with the ins and outs of law enforcement vehicle tracking applications. Make sure he can support you with training, as these systems are far too complex to be delivered in a plain brown wrapper with no after-sale support. And stay away from any system that is priced significantly below the others.  There is no such thing as a free lunch. Expect to pay between $5000 and  $7500 for a serious system, 50% to 75% more for a 360.

 Request a demonstration if you have any question at all about either  the unit or the vendor. Any vendor of a quality piece will welcome the opportunity to put his unit up against the competition. Travel, etc. is  not free, though, so have some consideration for the vendor's overhead before asking him to travel and demo is unit. A fair policy is a  minimum reimbursement for T&L expenses, possibly refundable with on a subsequent purchase.

 Earlier in the article we gave a list of accessory items to keep in your bumper beeper bag of tricks. The putty knife is for scraping away undercoating, grease or other crud from the surface to which you will  attach the transmitter. The plastic bag is for putting the transmitter in at the end of the surveillance, since it will be greasy and muddy. Keep the transmitter in the bag until you can clean it up, so it won't get your car all grubby.

 The hand cleaner towelettes are for wiping off  your hands after you've removed the unit, before the grease can rub off on your vehicle's upholstery. The small penlight is for seeing under the vehicle when you're installing the transmitter - even in daylight it helps to have some light on the area. I use a minimag or, more recently, one of the new micro streamlights that's about the size of a lipstick. The reason for a small light is that you can hold it in your  mouth when you need both your hands free. And, when you're covertly installing the transmitter, you usually don't want to be seen carrying a whole bunch of stuff up to the target vehicle.

 I guess we should discuss actually installing the transmitter. Contrary to the name, the bumper is usually not practical to conceal the beeper  transmitter. You want a flat surface big enough for the magnets to sit  flat. Do NOT use the gas tank as the metal there is too thin for the magnets to attach securely. We've never had a transmitter fall off although it does happen occasionally. Pick an area where the transmitter will be hidden from casual view, not buried too far up in  the vehicle.

 The transmitter does not have to be mounted to the rear of  the vehicle, although it doesn't hurt to have the signal radiating to  the rear, presumably towards your car. We have had the best results with a frame crossmember, frame rail, or occasionally up inside a fender well. Scrape the area clean with your scraper. It's not necessary to get down to bare metal, although it sure doesn't hurt. If at all possible, reinforce the mounting with either the duct tape or  the electrical tape, whichever seems more practical at the time. Use  several wraps completely AROUND a frame rail for the most secure mounting. Make sure you do not use one of the gaudy silver colored duct tapes.

 Try to place the unit so that the antenna can poke out in the clear as  much as possible. If you can, keep the antenna vertical and don't let any part of the antenna come any closer than necessary to any other  metal - always keep it at least 4 or 5 inches from any metal or find another location. Select placement and antenna orientation such that  the transmitter is not likely to be "wiped off" if the antenna hits brush, a curb or crap in the street. And it should go without saying  not to mount the thing on any component of the exhaust system... With experience you eventually will develop your own techniques for installing and removing the transmitter so I won't say too much more  here.

 Transmitters have a certain amount of weight if they are to have any  useful battery life and range. Our unit has the magnets sort of shock mounted so that the rubber shock absorbers soak up the bouncing around of the unit while the car is moving. Without some sort of shock  mounting all that force is transferred directly to the magnetic coupling, which is likely to break loose and let the transmitter fall  off without the buffering. Again, experience and appropriate design for  the application.

 Are these things legal? Well, I'll take the standard cop out and say  that we don't render legal advice. Ask the State's Attorney. In this  state, he has rendered a verbal opinion that no privacy is being  violated, as one has no reasonable expectation of privacy in regards to one's vehicle's presence on a public roadway. And, no interception of  written or spoken communications is involved. There is an incredible  amount of fiction related to beepers. I have never heard of anyone,  anywhere having the slightest problem related to these devices. Of  course, don't trespass to install the device. In the situation of a domestic investigation, frequently the vehicle in question is jointly  owned and the client party can give you permission to install the  device. Sometimes semantics is involved. We have been hired to install  "executive protection" beepers, to allow us to track and locate a subject and vehicle if they are taken. We've also sold them as "route verification" systems, to let a fleet operator keep track of the movements of his delivery vehicles. Don't do anything stupid, get a  legal opinion, and you'll probably be OK. I can't help you too much here as the legal questions are dependent on local regulation.

 Another aspect to investigate is FCC type acceptance of the transmitter. VERY few transmitters advertised for vehicle tracking are  type accepted, and a unit that isn't is subject to confiscation and harassment of the owner by the FCC. I would go so far as to say that you probably shouldn't buy a transmitter that is not type accepted  unless you are a bona fide government agency. There is an excellent chance of a supplier being approached by the FCC and ordered to turn over a list of all purchasers of a non approved device. All purchasers  would then be contacted and directed to turn in the illegal transmitters. This has happened quite recently and cost some friends a lot of money. Our ORION unit, by the way, is type accepted. Call us for  the FCC registration number if you need it. Any FCC type accepted device will have a permanently affixed metal tag to that effect stuck to the unit. I have seen more phony type acceptance stickers than I  have real ones, so don't be afraid to ask the manufacturer for a  statement in writing that his unit is approved for vehicle tracking  applications.

 Care and feeding - replace all batteries EVERY time the unit is issued. No matter how little use the current set of batteries has had, replace  them. Keep new batteries in the refrigerator and write the date on them so you can use the oldest ones first. Batteries are insignificant in cost compared to the consequences of blowing an investigation. Unless your unit is in constant use, I recommend throwaway batteries as opposed to rechargeables. Rechargeable batteries will save you money in  the long run, but their operating life per charge is maybe a third of  that of throwaways.

 Rechargeables also require some special care to avoid problems which are especially serious in vehicle tracking operations. Use the best alkalines you can get, or even lithiums if you  need extremely long life out of the beeper. If the weather is very cold the performance of the batteries will suffer, so keep the unit in a warm car until the last possible moment. Conversely, do not let the  batteries get too hot in the summer or their life will be reduced considerably. Batteries have their internal connections made by  crimping, which occasionally can go intermittent under the severe  vibration usually experienced by the transmitter.

 To add a bit of redundancy, our ORION unit has three batteries in parallel. Should one open up, the other two will still carry the unit for 36 to 48 hours.  And, of course, three batteries offer longer life than two. Replace all  batteries at the same time, and do not mix battery types or use anything other than all new, similarly handled batteries. Used  batteries removed from a little used beeper can still be used in  radios, toys or other electronics, so they needn't be wasted. Just make  sure you label them so previously issued batteries don't get cycled back into the system. Please don't compromise a five or six thousand dollar tracking system for the sake of five bucks worth of batteries.

 Be very careful of the receive antenna coax. Don't squash it in the car door or roll the window up on it. Also don't kink the coax or coil it up too tightly in storage. Coax is relatively fragile stuff and must be  in near perfect condition for your tracker to work right. If (when) the  coax starts to deteriorate, the entire antenna assembly must be returned to the vendor for service. For all practical purposes it is not possible to replace coax on the receive antennas in the field as the lengths, type and even brand of coax is all precisely tuned. Any  deviations here and the system will not read accurately. Keep an eye on all connectors too, both in the antenna system and power or remote console cables. Fix anything not perfect. Examine the beeper's antenna  every time out, too, and be certain to tag the unit as bad and turn it  in for repair if it needs it. Don't forget about it until the next clown signs it out for his surveillance. If you use a tracker regularly  it doesn't hurt to have a spare transmitter around. Make sure it is on  the same channel(s) as your receiver BEFORE you issue it.

 As in any other surveillance equipment package, it's a good idea to have a check off sheet listing all components and accessories necessary for the job. Make sure everything is checked off before the unit is  issued.

 Well, that's about all I'm going to cover on the topic of bumper  beepers. We've discussed quite a bit but, for some reason, whenever I  finish a series of articles on a topic I feel like I've hardly  scratched the surface. If you have questions on any aspect of vehicle  tracking I haven't covered, feel free to call us at (410) 879-4035 and ask for me personally. If you need service we'd be glad to help you or refer you to someone in your area. I'd also like to hear from you with  comments on this series. And, as always, we're always soliciting ideas  for future articles. Let us know what will help you. Thanks for your  support and I'll look forward to meeting many of you in person this year or over the phone. We exhibit at most major industry trade shows,  so look for us or one of our dealers displaying our logo.

 Bumper beepers are a tremendous asset to the serious investigator. Read both parts of this article and keep them around for reference, even if  you don't yet own a unit. If you are currently using a beeper, you know what I mean. If you're not - give it some thought. Following subject vehicles is such a major part of our operation. Any piece of equipment  to let you do that job more efficiently is worthy of serious  consideration. The units are not inexpensive - but neither are vehicles, radios, video equipment and everything else in our black bag.  Don't be intimidated by bumper beepers. A quality unit from a reputable manufacturer will work well, save you many hours and ensure more successful surveillances. The manufacturers have spent many thousands  of hours and huge sums of money to produce these units for you - the  investigator. Let technology make your job easier.

 See you next issue. Thanks for your support.

 Copyright (C) 1987 by Steve Uhrig, SWS Security.