Regenerative Detectors

Author: J.B. Hoag

Fig. 17 I. A simple regenerative detector. (L3 has from 10 to 25 per cent the number of turns of L2)

Figure 17 I shows a grid-leak detector, like that described in the preceding section, to which has been added a tickler coil L₃ for regenerative feedback. The feedback increases the amplification very much. With L₂ and L₃ wound end to end and in the same direction, connect the plate lead to the outer end of L₃, and the grid lead to the outer end of L₂, in order that the feedback will be regenerative. The variable bypass condenser C₃ (maximum of 100 pF. or more) is used to control the amount of regeneration. When it has a large value, its reactance is comparatively small and the regeneration is greater. When C₃ exceeds a critical value, the circuit breaks into oscillation. These oscillations are useful for the reception of code but must not be present for the reception of a speech-modulated carrier wave. The circuit is most sensitive just before it goes into oscillation. For code, C₃ should be set so that the circuit just begins to oscillate.