This circuit was obtained from HAM Radio magazine in an 80's issue. The FETs are types of the time and the frequency is determined by the crystal. The circuit operates at voltages from 3 to 9 V.
This detector or window comparator was suggested by Harris in documentation from the 90's. The...
This circuit was found in the April 1971 Radio Electronics magazine. It uses common transistors and can...
Found in Radio Electronics from the 90s, this circuit uses a thermistor or NTC. The resistance of the...