Abstract: There is disclosed a technique for measuring the magnetic field of a sample, such as sheet material having one or more magnetic poles, including effecting relative movement between a magnetically responsive transducer and the sample to scan the magnetic field while controlling the distance between the transducer and sample. Apparatus is provided to practice such technique, including control of the relative scanning movement, and of the transducer/sample spacing. A breakaway support for the transducer prevents damage in case an obstruction is struck, and a circuit operates on the analog signal produced by the transducer to provide useful output information representative of the magnetic field.

Abstract: In accordance with the present invention, a single shunt feed mechanism, including a single gamma section and a single impedance matching circuit, is employed to enable an antenna tower as an effective radiator in plural wave length bands without having to alter the upper tie point of the gamma section to the antenna tower. In one embodiment, the shunt feed of the invention enables the antenna tower as an effective radiator in either two of the adjacent bands mentioned, namely the 40 and 80 meter bands or the 80 and 160 meter bands. In accordance with another embodiment of the invention, a single shunt feed mechanism, including a single gamma section, a single impedance matching circuit, and a filter, enables an antenna tower as an effective radiator in all three of the indicated bands.

Abstract: A first transmitter-receiver movement detector system operable at a first frequency detects a train approaching a first grade crossing or other track location in response to train approach speed and distance, and a repeater receiver movement detector device also operable at such first frequency but located at a subsequent grade crossing or location, which is relatively proximate the first, is capable of looking through the first crossing even under unfavorable ballast conditions thereat to detect an approaching train with respect to its speed and distance from the second crossing. The output of the repeater receiver and that of a further transmitter-receiver movement detector system operable at a different frequency from the first are combined in a logic circuit to provide safe, minimum signal down time at the subsequent location.