Abstract: A received signal whose frequency band is spread in a spread spectrum system is subjected to fast Fourier transform processing to be transformed to a frequency spectrum, based on this frequency spectrum, a narrow-band interference signal is detected and eliminated, and then by subjecting the received signal to inverse FFT, the received signal from which the interference signal is eliminated is obtained, whereby the narrow-band interference signal can be eliminated from the received signal by a simple configuration.

Abstract: A received signal whose frequency band is spread in a spread spectrum system is subjected to fast Fourier transform processing to detect an interference signal, based on a result of the detection, a frequency characteristic of a frequency variable type notch filter for eliminating a narrow-band interference signal is controlled so that a narrow-band interference signal is eliminated from the received signal, whereby a spread spectrum communication system receiving device resistant to narrow-band interference can be provided by a simple configuration.

Abstract: The present invention relates to a radio transmitter-receiver and its object is to provide a frequency diversity communication device which can synthesize two carrier waves by one demodulation circuit without requiring any means for changing over the carrier waves and judging the receiving conditions.

Abstract: A vertical amplifier apparatus with a beam-finding function for an oscilloscope including an analog multiplier and a gain control circuit. The analog multiplier multiplies an input signal to the vertical amplifier by a gain control signal. The gain control circuit outputs a DC voltage as the gain control signal. In a beam-finding mode, the gain control circuit supplies the analog multiplier with the gain control signal whose absolute value is much smaller than that of the gain control signal in a normal mode. This makes is possible to obviate a dedicated beam-finder circuit. In a multi-channel oscilloscope, the beam-finding operation can be performed independently for each channel.