The integrated circuit used in this configuration for noise reduction on FM radios is not common today. The circuit is from 80s documentation and the reduction rate obtained is in the 10dB order.
This 4-transistor signal tracer or follower was found in Radio Electronics magazine from May 1960....
This 1967 Raytheon circuit uses an optical coupler of the era and has a range of 800 to 200 Hz....
Assembled with SMD components this circuit can be very small. The range is a few tens of meters. We...