Ground velocity sensor with drop-out detection.

摘要

A transmitter (22) emtis a signal at the frequency of an oscillator (32). A reference phase-locked loop (34) provides a corresponding reference velocity voltage (Vt). The reflected signal is received by a receiver (24) and processed by a second phase-locked loop (48) which provides a Doppler velocity votlage (Vr) which is corrected by subtracting (58) the reference voltage (Vt). In order to avoid spurious response by the second PLL (48) a drop-out detector (46) provides a drop-out signal (D/O) when the amplitude of the received signal (fr) is below a threshold (Vth). The drop-out signal causes a low-pass filter (52) in the second PLL (48) to hold its output unchanged for the duration of the drop-out. A digitally implemented embodiment is also disclosed.