This circuit can be used as a shield for touch control. The circuit can use any common FET like the BF245 and should never be powered by a source without a transformer.
When the voltage exceeds the value given by the zener, this circuit from a 1990 documentation...
This circuit for the 11-meter band, operating at 29.255 MHz was found in a Radio Electronics dated...
Found in a Popular Electronics from the 9s, this circuit has output for RS-232 interfaces and current...