Abstract: A marine radar transmission and reception system in which first and second transmission pulse radar waves are emitted as first and second pulse radar waves from first and second radar antennae or a common radar antenna; reflected waves of the first and second emitted pulse radar waves are received as first and second received pulse radar waves by the first and second radar antennae or the common radar antenna; the modes of the first and second transmission pulse radar waves are selected in cooperation with those of the first and second radar antennae or that of the common radar antenna so that the first and second received pulse radar waves may be received by the first and second radar antennae or the common radar antenna independently of each other; a quotient or difference output corresponding to the quotient or difference of the first and second received pulse radar waves or the first and second received outputs based thereon is obtained; and sea clutter eliminated received pulse radar waves or outputs bas

Abstract: A gyrocompass having a gyro rotor, and a device for applying to the gyro rotor about its vertical axis a torque in proportion to an inclination angle of the spin axis of the gyro rotor from a horizontal plane so as to attenuate the north-seeking action of the gyro rotor, in which the torque is controlled to be proportional to the inclination angle for its component which varies with a period same or close to that of the north-seeking action while to be approximately zero for a component of the inclination angle which does not vary.