# If the pseudorange is not fixed, how does a receiver lock/fix onto a satellite signal?

If the satellite moves around the orbit at a velocity, the pseudorange between the receiver and the satellite should be changing right? If so, how does a receiver lock onto a satellite signal if the propagation delay keeps changing as well?

Shouldn't the receiver would need to constantly readjust to find the correlation of the signal, or am I getting the wrong idea here?

• The GPS signals are derived from a base clock signal of 10.23 MHz. To compensate all relativistic effects, the base clock is 10.23 MHz - 4.55 mHz. The received signals on Earth are then derived from a 10.23 MHz,. Not the receivers are corrected but the satellites. With the correction, locking of a receiver onto a satellite is possible.
– Uwe
Commented Sep 29, 2022 at 4:30
• @Uwe Does a receiver remains locked onto a satellite as long as the signal is visible? Commented Sep 29, 2022 at 7:43
• Shouldn't the locked signal keeps getting interrupted if the satellite keeps moving thus affecting the time it takes for the signal to reach receiver? Commented Sep 29, 2022 at 7:46
• @Uwe The satellites can't correct for the shift due to their orbital speed. This depends on the direction of the receiver and is different for every single receiver. Commented Sep 29, 2022 at 9:58
• @Uwe The receivers are constantly correcting themselves, not only for the changing frequency of the received signal due to Doppler shift, but also for the changing frequency of the receiver's commercial off-the-shelf oscillator. The GPS satellites have top-notch oscillators; they have atomic clocks onboard. Commercial receivers do not use atomic clocks internally, so their oscillators vary with manufacturing variances, temperature, etc. Dealing with these variations is a solved problem. Commented Sep 29, 2022 at 15:06