This circuit makes use of a special LM195 power transistor not very easy to obtain. The circuit is from the 1994 Linear Applications Handbook by National Semiconductor.
This TTL circuit for digital signals up to a few dozen megahertz was found in old documentation, but...
This circuit with an operational amplifier was found in the magazine Radio Electronics of...
This detector is from the 1990 Motorola Dataar Databook, but can be adapted to work with more...