21. The tone is modulated using frequency shift keying. 22. In this approximation, the frequency shift is not affected by the direction of the optical radiation. 23. As a result, the frequency shift arises. 24. To pick up moving targets, the radar looks at the Doppler frequency shift of the returned signal. 25. The frequency shift can be calculated, by: 26. The only effect in known physics that can cause a uniform frequency shift is the Doppler effect. 27. A frequency shift keying ( FSK ) signal is alternating between two waveforms, and allows passband transmission. 28. This gravitational frequency shift is noticeable. 29. However, non-linear sweeps have to be used with caution when target returns are affected by Doppler frequency shifts . 30. Frequency is folded for high speed targets where radial velocity produces a frequency shift above the Nyquist frequency.
