Path delay

From DictionGloss

The signal delay between a transmitter and a receiver. Path delay is often the largest contributor to time transfer uncertainty. For example, consider a radio signal broadcast over a 1000 km path. Since radio signals travel at the speed of light (with a delay of about 3.3 microseconds/km), we can calibrate the 1000 km path by estimating the path delay as 3.3 ms, and applying a 3.3 ms correction to our measurement. The more sophisticated time transfer systems are self-calibrating, and automatically correct for path delay. Path delay is not important to frequency transfer systems, since on-time pulses are not required. However, variations in path delay do limit the frequency uncertainty.