Weren't we talking about a cheap toy car with omni-directional transmitting and receiving antennas way too short at 27MHz for efficiency?
Doesn't its receiver use only a single transistor without automatic gain contol?
You do realize this thread is from 2005? Have you read it yet? Building from scratch would be quite a challenge, even if you had some decent test equipment. Toy cars are cheap, hobby R/C transmitters/receivers aren't too expensive these days either. Plenty of reasonably priced modules the interface easy with microcontrollers. Can't imagine just building a pair, just for fun. I've only built 3 transmitters, and didn't get much range from any of them, and poor reception. The video transmitter was even a kit.
Here is the transmitter and receiver schematics for a $10.00 radio controlled toy car. Its range might be 10m. Its control is just on and off with its motor.
The transmitter is not modulated but has a crystal for frequency accuracy.
The receiver is a one transistor super-regen. I guess it amplifies the squegging frequency when it receives a carrier frequency.