This elaborate mixer is from an Electronics Today International from the 80s. Operational amplifiers are common and resistors with no value determine the gain of the amplification steps.
This circuit appeared in the June 1990 issue of Radio Electronics magazine. Integrated circuits must...
Lockout shooting, due to the incidence of light, can be achieved with the circuit in the figure. In...
This circuit can function either as a crystal or galena receiver with a pre-amplifier using a FET...