#### In Depth

### Doppler shift

#### Whenever a signal source moves towards or away from a receiver, the frequency of the signal as observed at the receiver increases or decreases respectively. This is known as the Doppler effect. The degree of frequency shift is a linear function of the speed of motion and the carrier signal frequency. For example, a source moving at 70 mph using a carrier frequency of 900 MHz will experience a Doppler shift of up to +/–100 Hz at the receiver. |

#### Correcting for Doppler shift can be very difficult, particularly in a multipath environment, where signals arriving from different angles experience different Doppler shifts.

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