(10) The use of Doppler radar for speed detection and enforcement on the roads is very common and has been in use for a long time. Suppose a 10 GHz radar (also called radar gun or speed gun) measures the speed of a car at 120 km/h moving towards the radar gun. a. What is the change in the frequency of the reflected wave due to the speed of the car b. Calculate the sensitivity of the device in [Hz/km].

The sensitivity of the device = 1.234 Hz per km

Explanation:

Given  

Frequency (f) = 10 gHz

Speed of the car = 120 Km/h

As per the doppler’s effect

V = (change in frequency /frequency) *(c/2)

Substituting the given values, we get –  

Change in frequency = {(2*10^9*120)/(3*10^8)} * (1000/3600)

Change in frequency =  37.03 Hz

b) speed of light = wavelength * frequency

3*10^8 = wavelength * 10*10^9

Wavelength = 0.03 m

Sensitivity = change in frequency /wavelength = 37.03/0.03 = 1234 Hz/m

1.234 Hz per km

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