Measuring speed with acoustics and a tape recorder...
Philly, are you referring to those cars that run in circles on a control line. Those won't work for doppler because they don't go in a straight line. I suppose there is a highly complex formula that could be used to compensate for the path, but you'll need a degree in mathematics to sort it out. hehe.
I've improved the quality of my graphs by not pumping the recording directly into the PC using Line-in. Rather, I'm using "Scan Input" and playing the tape recording into the mic. I don't get the signal over strength (blob on graph) problem and it's much easier to queue up and analyze a pass by manipulating the microcassette tape, rather than a wav file.
Jason