This circuit was found in a Radio Electronics from 1970. The coupler with LDR is from that time, but the circuit can be adapted to use modern components and act as a shield.
This 1987 signal injector included the power supply from the power grid. The transformer is 6 + 6...
This amplifier was found in a 70s documentation. The product gain x bandwidth is 350 MHz. The...
This simple receiver with junction FET uses a high impedance magnetic earphone (over 2 k). Power...