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.