Found in a 1964 Electronic Design this circuit compares two signals by providing the inverse of the algebraic sum of their frequencies. The circuit can be made with modern equivalent transistors.
In the figure we have the way to use a single control voltage to act on two varicaps...
This oscillator provides a 1 MHz rectangular signal determined by the capacitors used. The circuit...
This shield circuit with an optical coupler was found in an 90s EDN. The circuit can be used with...