A Simple V.O.X. Circuit
G8MNY
Here is a 3 transistors 4 diodes circuit that is a Voice Operated Tx PTT control as well as an ANTI VOX circuit to stop mis-operation from Rx noise.
The BC109 Mic high gain amp is RF protected by the Ferrite Bead on the base lead. Its' O/P is voltage doubled and the DC stored in the double time constant to give fast response and slow decay time. The rectified DC is referenced from the +ve rail, is put across the 220K VOX gain control for a time determined by the 220K decay variable control that discharges the caps.
The gain controlled sample of the DC switches on the PNP which turns on the NPN PTT drive transistor. The 10M
發表於 29-12-2006 11:33:32