Found in a Hands On Electronics from the 80's this circuit allows the reading of low resistances in a common multimeter. The circuit consists of a constant current source.
The signal itself captured by the (long) antenna serves to feed this simple experimental circuit....
In the figure below we have two triggers made with the LM3900 transconductance operational...
This common circuit using a multivibrator causes two lamps to alternately flash at a frequency and active...