This circuit is for traditional old-style telephone lines found in an American 1980s documentation. Components are common and the optical coupler can be replaced with an equivalent.
We found this relaxation oscillator in a 1967 General Electric documentation. The frequency is given...
This circuit was found in the September 1984 issue of Radio Electronics magazine. The circuit has...
Although the BD135 transistor is not specifically for RF applications, some of them can easily...