Found in Ferranti's 1968 documentation, this circuit uses a Darlington photo transistor to drive a 12V relay. The circuit can be implemented with modern equivalent components.
This circuit, found in US documentation, can measure the power of transmitters up to 10 W, given...
This second-order filter was found in a 1978 publication and can use common operational amplifiers like...
I found this circuit in a 1992 Electronics Experimenter Handbook. The circuit can be easily...