This space mark demodulator for FSK signals was found in an American telecommunication documentation from the 1980s. The circuit operates with 2025 Hz and 225 Hz mark space signals.
In the figure we have the way to obtain 500 gain from a FET. FETs can be BF245 or MPF102. The...
With the circuit shown in the figure, we have a logic signal to activate a calling device when...
Found in 1980s Electronics Design, this circuit covers 4 decades of frequencies with a unique...