This assembly derives from the AM radio receiver 1 project. Compared to the previous assembly, I added a positive feedback circuit, consisting of the Cr capacitor and the L3 coil. The two components are connected between the transistor collector T1 and ground, according to the wiring diagram.
The role of this circuit is to take over part of the radio frequency signal from the collector of T1 and to bring it back to the input of the radio frequency amplifier.
In this way, a higher sensitivity and selectivity of the radio receiver is obtained. Basically, you can receive radio stations located at distances of over 1,000 km.