DTMF Decoder (CB25048E)

This circuit was found in the 1987 Radio Electronics magazine. The components used are integrated circuits of the time.

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Tuned Band Notch Filter LM107 (CB15472E)
An interesting and versatile filter circuit, suggested by National Semiconductor is the one shown...
Symmetrical 15 V power supply (CB8498E)
Found in na 1970 EDN this circuit has a parallel regulation providing a symmetrical output of 15 V....
Telegraph manipulator (CB7038E)
This circuit was found in an American magazine 73 for radio amateurs of the 80s. It is an...