Abstract: An improved seal for a rotary drill bit includes a pair of ring seals comprised of dissimilar materials disposed axially, adjacently to one another intermediate a stationary journal and a rotating cutter to present multiple sealing interfaces so that one or more of the ring seals may rotate with respect to another or the journal or rotating cutter. One of the ring seals may preferrably be fabricated of material exhibiting elastomeric characteristics.

Abstract: A microphone of the hand held type used in portable or remote radio communications systems in which improved resistance to shock, wet environmental conditions is achieved by using a resilient mounting means for a receiver disposed inside a hollow housing which includes a stop for limiting motion of the receiver in the resilient mounting means and through the use of a loosely mounted water impervious membrane over the active side of the receiver and further disposing an open cell, foamed plastic element over the outside of the plastic membrane.

Abstract: A digital frequency synthesizer in which a BCD.div. N counter is used to provide the desired frequencies of operation without requiring further BCD decoding operations to provide direct channel number interface. This is accomplished by selecting a value of (N) corresponding to a desired channel number (CN) and selecting a downmix heterodyning frequency so that the lower order bits of (N) are equal to the desired (CN) without need for further conversation.