A colleague of me bought two identical rc cars for christmas as gifts for his sons. The problem was that the remote control of both cars work on the same frequency. The boys will not be able to use both cars at the same time.
The cars are sold in Germany only in one product version. There is only on 27Mhz version.
I think the car is not sold worldwide. To get an Idea what I am talking about have a look here:
However, the method I describe here should work with nearly every rc car. I tore different cars apart and always found nearly the same technology inside.
An other Teardown
Step 1: How does it work?
On the transmitter side a quarz chrystal is used to keep the transmitter on the defined frequency. In our case it is 27.415Mhz. The transmitter needs to maintain a stable frequency, that's why the quartz crystal is used ( http://en.wikipedia.org/wiki/Crystal_oscillator ).
On the receiver side no quartz crystal is used because it costs to much money. The stability of modern receiver circuits is good enough for a simple toy. To make the receiver work it needs to filter the radio frequencies to detect only the signal sent by the transmitter ( http://en.wikipedia.org/wiki/Receiver_(radio) ). There is at least one filter mounted on the input, near the antenna. While using superhet ( http://en.wikipedia.org/wiki/Superhet ) technology there is also a if band filter needed. Most of the time this is a small ceramic resonator.
Looking at the Wikipeda article you will find a picture under "Design and its evolution". The block named "RF Amplifier" is the place where the first filter, designed with a coil and a capacitor, sits. The second filter, the resonator, is marked with "Filter".
I added a "partly re engineered" schematic of the input filter. "Partly" means, that only the important components are drawn.