Friday, January 10, 2014

Car Fob Transponder

Car fobs (remote keyless systems) are small transmitters. It's also branded as "keyless" entry or "remote central locking." But no matter the make and model it has a RFID and/or touch controlled transmitter. (To ease my typing lets call it an RKS.)

The first RKS debuted on the Renault Fuego in 1982, a French-made autombile. It was sold in the United States through American Motors (AMC) dealerships. It tanked in the US but did fairly well in Eurpope and was a popular Coupe in the UK.  But the RKS feature gained popularity in the U.S. and was available on on several GM vehicles by 1989. RKS were predated by infared systems like those on certain Mercedes-Benz and BMW models.

The car fob  contains a  low powered radio transmitter. Their range us usually on the order of 15 to 60 feet. When you push a button the fob sends a digitally coded radio signal to a receiver unit in the car which executes the command.

Most America-made RKS operate at a frequency of 315 MHz. In Europe and Asia most RKS operate at 433.92 MHz.While all RKS use encryption to prevent unwanted access none of them are fool-proof. Later systems included a "smart key" which had an RFID on the fob. These vehicles couldn't be started unless that fob was within close range of the vehicle. In this application the RKS can also operate as a transponder and responds to a signal  from the car with a digital code. This became a common function in the mid 1990s. More here and here.