PASSIVE FREQUENCY DETECTION CHANNEL FOR A DATA RETRIEVAL SYSTEM

摘要

A passive frequency detection channel utilizing shared crystal resonators respectively coupled to opposite ends of a center tapped secondary transformer winding. The crystal resonators are coupled to a passive current summing network and envelope detector and post detection integrator by means of a shared resistor isolation network. Current summing is provided by the resistor isolation network while the envelope detector is comprised of one of a pair of Schottky barrier diodes commonly referred to as hot carrier diodes coupled between the isolation network and a post detection integrator comprising a parallel R-C circuit. Additionally the R-C circuit in combination with both diodes provides a low AC impedance to ground for the crystal resonators and isolation network which is essential for proper operation of the apparatus.