This circuit was found in Radio Electronics from the 90s. The CMOS integrated circuit is a PLL not easy to obtain today. The output stage can be exchanged for another one with greater power.
This circuit for signals up to 30 MHz can improve your reception in the medium and short-wave...
This circuit was found in an 80's General Electric documentation. The circuit uses uncommon...
Found in Popular Electronics this circuit will trigger a buzzer if the ignition key is removed...