Found in documentation from 1924, this receiver has several sets of coils. Power is supplied by several batteries and listening on high-impedance headphones.
This circuit was found in a Popular Electronics from the 90s. The circuit has 4 frequency ranges...
The Texas Instruments INA826S Instrumentation Amplifier Evaluation Module is available from Mouser...
In the figure we have the way to control a flip-flop with the 4069 from positive pulses. The...