We found this circuit in an Australian publication from 1991. It is a kit of the time with input for a guitar pickup. The range is a few tens of meters.
This circuit was found in the Linear Applications Handbook by National Semiconductor. It uses...
This temperature compensated circuit was found in a Popular Electronics from the 90s. Integrated...
This circuit can operate with 27 MHz transmitters, having been found in a Japanese publication from 1967....