Found in American documentation, this circuit for modulated infrared signals can be tuned to a certain frequency. The photodiode can be of any type.
This twisted pair exciter circuit uses 80's components. The circuit is from a documentation of the time, but...
Based on Radio Shack 276-137, this circuit was found in the December 1995 issue of Electronics Now magazine....
Placed near a telegraphic transmitter (CW) and with a small antenna or pickup, it reproduces the...