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.
We found this circuit in a documentation for 1977 American radio amateurs. The LM336 integrated circuit...
The frequency of this oscillator depends on the coil and the 10 nF capacitor. The circuit is from...
This circuit can work with the previous one generating signals, that can be decoded by it. The...