Abstract: 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, an adjustable notch filter, a bandpass receiver and a digital controller, plus the software that runs in the digital controller. The signal detector circuit has an antenna, a preamplifier and a group of "fixed" filters. The adjustable notch filters are four circuits, each includes an active notch type filter stage with a DAC (digital to analog converter) in series with the input resistor to allow gain control and another DAC that controls the current through a diode that is optically coupled to a light dependent resistor pair. The light resistor pair 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.

Abstract: A communications link having a position capability responsive to either a manual or remote control actuation. In one embodiment, a remote carrier has a navigation system for outputting signals representative of the carrier location or position. A frequency shift key (FSK) modulator is connected to the navigation system for tone coding the carrier position signals, a transmitter of a transceiver is connected to the modulator for transmitting the carrier position signals, and a position enable switch for controlling selectively the transmittal of the carrier position signals.