A related difficulty is the need to reset the degree of regeneration as the detector is tuned. In spite of these problems the increases in sensitivity to be gained through the incorporation of this powerful technique have not been totally lost on the minds of the engineering community. Goaded on by this understanding, a few years ago Dr. Sutton set out to develop a positive feedback antenna circuit configuration that would be very sensitive to low level fields while at the same time being resistant to the influence of stray capacitive and inductive reactances. Figure 1 is a schematic diagram of a circuit that was developed which satisfies these requirements. Amplifiers A1, A2 and A3 may be Precision Monolithics OP-27s.
Electrostatic shielding is provided to reduce capacitive coupling between the two windings.
U.S. Patent No. As the specific design problem was development of an optimized broadband ELF magnetic field sensor, an active antenna with a wide frequency response also a criterion. This posed a design challenge as in a typical tuned antenna circuit significant antenna current, and thus maximum sensitivity, is only present with conditions of resonance. Under normal circumstances, peak resonance occurs at some very specific frequency where inductive reactance is canceled out by capacitive reactance. The innovative solution was to add a second feedback loop to the circuit which introduces negative inductive reactance that works in place of circuit capacitance to tune out inductive reactance.