What is a transponder?
A transponder is short for: transmitter
The word came into use around 1944. In basic terms a transponder is a
miniaturized electronic chip that has what is called nonvolatile memory.
Nonvolatile memory is the type of memory that does not need constant
energy for retention. Along with that electronic chip is a set of
windings, very fine wire coiled around a tube. These windings
look similar to the windings you would find in a electric motor.
There are two basic types of transponders. The first are the Electric
Coupled Transponder systems. Electric coupled transponder systems
are not limited to small areas for transmission but can transmit
messages or signals for different ranges of distance including several
inches to miles, as used in Satellites and Airplane's. These systems
require large amounts of constant electricity to operate.
The second type is what automobile manufacturer’s are using and
they are called Magnetic Coupled Transponder systems. Magnetic
Coupled Transponder systems are passive in nature. This means they
do not require constant electricity and thus do not need a power
source of their own. They operate in the frequency range area of
125KHz. Since Magnetic Coupled Transponders do not have their own
power source they are very limited to range of communication and
generally operate in the range of 1cm to 15cm. Since this is a
radio frequency it can penetrate materials that would make the
transponder not directly visible, such as the plastic or rubber in the
bow of a key.
The process of key identification is similar in most automotive
transponder systems. Once a key is inserted into the ignition lock and
turned to one of the ‘on’ or ‘run’positions, the induction coil that is
mounted around the ignition lock sends out an electromagnet field of
energy. The windings in the transponder chip absorb that energy and
power the electronic chip to emit a signal. The signal is usually an
alphanumeric set of digits which is considered the Identification Code.
The induction coil reads the signal and sends it to some type of
computer device to recognize the signal. If the signal is recognized as
being already in the computer’s memory the signal is accepted and other
electronic components in the vehicle are set into motion to allow the
starting of the vehicle or the continuation of the engine running.