Employing the XR2206 IC, this circuit was found in the May 1977 issue of Radio Electronics magazine. The formula next to the diagram gives the component values as a function of frequency.
This circuit was obtained from an American 80's documentation. The balanced mixer can be shown in...
This circuit was found in a 90s Electronic Engineering. The quadruple operational amplifier can be...
I found this circuit in an English publication from 1989. This configuration can be mounted with...