| 摘要 |
PURPOSE:To reduce CW-like interference disturbance that the Doppler device receives as much as possible by providing a wobbler oscillator which generates a signal varying in voltage periodically at a constant variation rate. CONSTITUTION:The wobbler oscillator 1 generates a saw-tooth wave. An FM oscillator 2 is modulated with the output of the oscillator 1 to generate an FM wave-which increases linearly in frequency. The output is amplified 3 and sent from an ultrasonic probe 4. An echo signal reflected by a reflection body is received by the probe 4, amplifed 5, and inputted to a beat signal generator 6. The signal from the FM oscillator 2 is also inputted to the generator 6 to generate beats of the difference between the two signals. Then a band-pass filter(BPF) 7 removes an unnecessary high frequency signal and a low frequency signal from the beat signal. Then the output is amplified by a low frequency amplifier 8 and converted by an AD converter 9 into a digital signal, which is processed by the Fourier transform of an FFT 10. Consequently, the CW-like interference disturbance that the device receives can be reduced as much as possible. |
