 
 MOBILE.TRACKING EQUIPMENT or "Bumper Beepers".....by The Mad Phone-man
 ------------------------------------------------------------------------------
 
 You remember the little "bug" installed on the.bad guys car in.the James Bond
 flicks.that allowed Bond to follow the.car from a distance? Well this file is
 a tutorial on them.
 
 First,.they do.exist, I've built my own, but even the best commercial units
 intended for law enforcement purposes wont do what the.Bond model purports
 to do,.that is, give a.printout on a moving map showing the route driven by
 the bug toter.
 
 The basics of the unit.are the.transmitter, which is about the.size of
 a pack.of cigarettes and is held on via a magnet. And a receiver, using 2
 identical antennas, coupled to.a center zero meter which gives.a heading
 towards the transmitter. More on these.later.
 
 The receiver/display unit is used by pilots, amateur radio operators, and
 law enforcement and security personnel.to track the movements of the
 transmitter
 usually at short ranges, the civil air.patrol uses these units.to find
 downed.aircraft by tracking the emergency beacon, activated by.the
 impact.of the crash. Amateurs play "hunt the fox" to keep illegal transmitters
 out of.the ham.bands. Law enforcement personnel track the movement of people,
 drugs,.and weapons by attaching a transmitter to the object (or suspect's
 car) to be followed.
 
 The transmitter is usually a small VHF.or UHF battery operated.package
 dangling a 19" flexible antenna (about the thickness of piano wire). The
 transmitter does not "beep" per say, but transmits a continual.carrier.
 The FBI uses 167.xxx mhz for theirs and the local DA uses the intercounty
 police.freq of.155.37..I have seen military models that use 149.xxx mhz
 around.here (air force).
 
 Now the receiver:
 Two identical antennas.mounted.on the chase vehicle (usually magnetic mounts)
 feed a.pair of.PIN diodes that.feed a phase detector which samples the
 receiver's IF output. When the.received signal.is directly in front of.you,
 signals arrive.at exactly the same time at each antenna. This is calibrated to
 read center 0 on the meter. (Incidentally the unit can't tell if the signal is
 in front or in.back of.you, so.the need to make sure you follow the subject
 reasonably closely is apparent). If the bug travels say to 10 o'clock on the
 compass rose, the needle will swing to.4 o'clock on the meter..The object here
 is to always drive towards zero and you follow.the bug.in the most direct
 direction. With a little practice,you can follow a subject on an adjcent
 street.without.loosing.him.
 The meter swings because the signal arrives later at one antenna than the
 other,.causing.a voltage change in the.phase detector (an Exar.Radio-teletype
 decoder chip in my model).
 
 Some recent units ive seen have Light emitting.diodes in a 360.degree circle
 and use 4 antennas. This gives.you full circle.detection capabilitys as the
 phase between pairs of.antennas is calculated also.
 
 Now, prevention:
 The easiest way to detect if you've been planted with one of these little
 transmitters, is to walk around the car or whatever with a portable frequency
 counter and check for an alien.RF signal. This.is also.the recommended
 method.to de-bug your home. A small freq counter with 1.2 ghz capabilitys
 sells for around $100..today. If you do find a.transmitter, have fun with it.
 Stick it on a train heading out of town, a Greyhound bus, or a.over the road
 tractor-trailer rig....my favorite is to stick.it on one of their own
 vehicles and watch them chase themselves....hehehe.
 
 The Mad Phone-man (c) 1988
 
 
 
