# doppler frequency shift

The doppler frequency shift is \(f_{D_n}(t) = v \frac{\cos \theta(t)}{\lambda}\),

If the transmitter transmits at \(f_c\) then the recieved frequency is \(f_c + f_D\).

So, if \(v\) is positive (distance between transmitter and reciever is reducing), then the recieved frequency is higher.

\(\theta\) refers to angle between reciever to transmitter and direction of motion. So, if reciever moves perpendicular to transmitter, i.e \(\theta = 90\) then there is no doppler shift.

Doppler has a greater effect on very small wavelength/very high frequency.