i think it not work by magic. Ok, this radar works with the doppler effect. It converts variation of frequency into frequency and it measures this frequency to display the speed. The variation of the frequency of the modulation is created by the impact of vehicle against the wave. More the speed of the vehicle is high, more the variation of the frequency will be high. At the speed of the light, the rythm of variation of frequency is the same as the modulated frequency. You can determine the output frequency if you know the modulated frequency value and speed of the car. the 74as series can be replaced with the 74hc but from what i know the 74hc is a CMOS type, is there 74hc in TTL type? i want to ask something? what is the major different between TTL and CMOS IC, the different that we can see from the IC... exactly like it shape or marking? I hope you can help me... :)