Abstract: A novel narrow-band communication apparatus comprises a digital signal processor for demodulating the output from a receiving section and outputting a modulation signal for an audio input, an electric field strength detector section for detecting electric field strength in the output from the receiving section, an indicator for indicating whether the narrow-band communication apparatus is in a receiving mode or in a transmission mode, and a power controller for controlling supply of power to, or an operating state of specified portions of, the narrow-band communication apparatus according to the output from the electric field strength detector as well as from the indicator.

Abstract: A novel narrow-band communication apparatus comprises a digital signal processor for demodulating the output from a receiving section and outputting a modulation signal for an audio input, an electric field strength detector section for detecting electric field strength in the output from the receiving section, an indicator for indicating whether the narrow-band communication apparatus is in a receiving mode or in a transmission mode, and a power controller for controlling supply of power to, or an operating state of specified portions of, the narrow-band communication apparatus according to the output from the electric field strength detector as well as from the indicator.

Abstract: For receiving radar waves entering an antenna horn by the heterodyne method, the system is designed so that one of the local oscillation signals produced respectively by a local oscillator for the X- and K-band radar waves, a local oscillator for the Ka-band radar wave, and a local oscillator for leaked local oscillation waves can be selected to be used as the first local oscillation signal for beating down the radar waves at a first mixer. When a radar wave has been detected in the Ka-band receiving mode with the local oscillator for the Ka-band being selected, a signal processing circuit sets the heterodyne receiving system to the leaked local oscillation wave receiving mode, selecting the local oscillator for the leaked local oscillation waves as the first local oscillator. If a radar wave is detected in this mode, the signal processing circuit inhibits a warning apparatus from issuing the regular warning.