Abstract: A magnetic recording medium is erased by mounting at least one magnet with its north-south poles parallel to the surface of the recording medium and transporting the recording medium in a plane horizontal to the north-south pole axis such that the magnetic field lines traverse the recording medium. The magnet may be mounted on an endless belt which moves substantially transverse to the direction of movement of the recording medium. The belt may be oscillated or moved continuously along its transverse path.In an alternative embodiment, magnets may be mounted on the end of an arm which is adapted to be rotated in parallel spaced relation to the surface of the recording medium. Also, a number of permanent magnets may be mounted in two rows in spaced relation to form an aperture therebetween for transport of the recording medium therethrough.

Abstract: The present invention is related to a mechanism for guaging the expansion of a trawl net in correspondence with the number of fish caught within the trawl. The mechanism includes sensors adapted to be fastened to the masks of the trawl net in order to sense changes in the geometry of the mask. Each sensor includes a permanent magnet and a reed contact disposed to be activated by the magent as a result of a predetermined trawl net expansion, thereby transmitting a signal indicative of such expansion to a detection and indication mechanism located on board an associated trawler.

Abstract: A method and means for recording auxiliary information, e.g. temperature readings, on echo sounder recorders or similar display devices, in addition to the normal recording, said information being presented as the distance of a recorded mark from a point of reference. In order to always secure a clear representation of such information, according to the invention the normal record on the display is blanked out or reduced in intensity adjacent said mark.

Abstract: An echo probe taps power from pulses received at an input/output terminal from a distance measuring system and generates delayed simulated sonar signals at the input/output terminal which have substantially the same frequency as the carrier frequency of the distance measuring system. Control circuitry produces spaced first and second control signals having different characteristics from one another in response to a received pulse from the distance measuring system appearing at the input/output terminal and actuates carrier frequency oscillator circuitry to generate the simulated sonar signals. Circuitry is provided for controlling the delay between the received pulse and the simulated sonar signals and also to determine the pulse widths of the first and second control signals and the spacing therebetween. Level control circuitry regulates the amplitude of the simulated first and second sonar signals.