What are 'Doppler shifts' in radio communications?

Doppler shifts refer to the changes in frequency or wavelength of a signal in relation to an observer moving relative to the source of the signal. In the context of radio communications, this phenomenon occurs due to the relative motion between the transmitter (source) and the receiver.

When the source of a radio wave moves towards the receiver, the waves are compressed, leading to an increase in frequency known as a "blue shift." Conversely, when the source moves away from the receiver, the waves are stretched, resulting in a decrease in frequency or a "red shift." This effect is similar to the way a passing ambulance’s siren changes pitch as it approaches and then moves away from an observer.

Understanding Doppler shifts is crucial for applications such as radar and satellite communications, where the relative speeds of objects can significantly impact the received signal's frequency, and consequently, the information being transmitted.