Abstract: YIG oscillator apparatus comprises both an FET-based YIG oscillator circuit and a bipolar transistor-based YIG oscillator circuit inside a single magnetic structure. Both YIG spheres are disposed in the single air gap of the magnetic structure, which is defined by a pole piece which is tapered to an elongated pole surface which is only slightly larger than necessary to cover both YIG spheres. A band reject filter is included inside the housing for rejecting second harmonics of desired oscillation frequencies only.

Abstract: YIG oscillator apparatus comprises both an FET-based YIG oscillator circuit and a bipolar transistor-based YIG oscillator circuit inside a single magnetic structure. Both YIG spheres are disposed in the single air gap of the magnetic structure, which is defined by a pole piece which is tapered to an elongated pole surface which is only slightly larger than necessary to cover both YIG spheres.

Abstract: To ascertain when individual foundry molds and cores, bonded by a chemical method, have reached the requisition hardness, or still have the requisite hardness, a probe is pushed into the mold or core with a predetermined force, then withdrawn, and after a time interval it is pushed into a fresh point on the mold or core. This is repeated a number of times, each time in a different place, until the penetration is less than a predetermined value, indicating that the requisite hardness has been reached. Apparatus for doing this automatically can be portable and may signal by lamp and/or sound when the hardness has reached the required value. It may be modified to check whether the hardness of a core or mold made some time earlier has fallen below a given minimum value.