This receiver was found in an article in Electronics Now magazine in March 1994. The coils are critical, as shown in the figure. Listening is through headphones.
This circuit monitors an old-style analog telephone line. We found it in the September 1991 issue...
In the figure we show how two diodes can be used to simulate the center tap of a push-pull driver step....
This circuit was found in a General Electric / RCA documentation from the 1980s. The circuit is...