This circuit was found in an American documentation of the 90s. Optical resources with the LDR as a lens can help in obtaining directivity and sensitivity.
This circuit is from a Radio Electronics from January 1958. The transistor is the CK722, and the...
This circuit with transistors was found in an old Japanese publication, translation of an American...
Found in documentation from the 90s, this circuit was used in communications receivers of the...