We found this circuit in the Electronics Experimenter Handbook magazine from 1993. L1 has 2 = 2 turns of 28 or 30 wire in the shape of 0.5 cm without core. The range reaches a few tens of meters.
This sophisticated function generator circuit appeared in the September 1972 issue of Radio...
We found this circuit in a 1975 publication. The circuit can be made with more modern equivalent...
The open output voltage on this circuit is approximately three times the peak value of the input...