| 摘要 |
<p>An auto notch system which automatically "notch" filters up to four interference signals (interferers) in the band from 50 KHz to 150 KHz comprises a signal detector (8), adjustable notch filters (22, 30), a bandpass receiver (38) and a digital controller (40), plus the software that runs in the digital controller. The signal detector circuit (8) has an antenna (10), a preamplifier (12) and a group of "fixed" filters (14,16,18). The adjustable notch filters are four circuits (108, 110, 112, 114), each include an active notch type filter stage having a programmable attenuator (109), a biquad bandpass filter (120) and a summer (122). The programmable attenuator has a DAC (digital to analog converter) (16) in series with the amplifier (118) to allow gain control and the bandpass biquad filter (120) has another DAC (308) that controls the current through a diode (144) that is optically coupled to a light dependent resistor pair (136). The light resistor pair (136) is in the filter loop and as the resistance varies the frequency response of the filter changes. Thus the frequency response is controlled by varying the diode current. The bandpass receiver (38) is used to sense and amplify the signal output of the Loran bandpass filter or the signal output of the notch filters under control of the controller. The bandpass receiver (38) is tuned by the controller to one of 128 specific frequencies in the range from 50 KHz to 150 KHz. The controller (40) tunes the bandpass receiver (20), selects its input signal source and controls the gain and frequency characteristics of the notch filters (22, 30). The software commands these hardware functions.</p> |
